04.4 ,
wan
‘ .t.‘
”mama?
‘
”may“.

at.
1L If
5.3. r ,
:ﬁwfun
‘ H. . Run
.253
.vnu‘ilizia
. . 2...!!!
. 31“
up
. 3:..th
. . . . 1593..
, : iiﬁéurrzu.
.. .3953!
151.. . , , .3...€.....
2.: s a. .. s- 5.?
a . . an ..

z...
gin
.35....

{am

5:...
{line
3933.25;
3...}.3343
4.1.3.. .9 .: 5.13am“;
.3. t 83:}. .Y
- 1.9.. .331; 3:
in 3.): 5...:

n. f...» tbs
2.: . ...
{l , xv . 5.3..
2...: .. "£33.:
.535... .
2..

,T .
{51.13% . .I

I»... . '55:.9f
I. 1.32.: 3:

 

THESIS
7

26:1: 131+
87%
TH s

- LIBRARY
Michigan State
University

 

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DQTE DUE

‘3

DATE DUE

DATE DUE

 

Y

05

 

OCT 0 3 mos

bvv

@Wélimos

 

IJLJKi a L‘J‘:

 

 

V‘n

 

 

 

 

 

 

 

 

 

 

11/00 mm.“

 

Maskless Patterning on CVD Diamond Films by Excimer Laser
By

J ong-kook Park

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY
Department of Materials Science and Mechanics

2000

ABSTRACT
Maskless Patterning on CVD Diamond Films by Excimer Laser
By

J ong-kook Park

Extensive investigations were conducted in this study to examine the excimer
laser ablation process for maskless patterning on chemical vapor deposition (CVD)
diamond ﬁlms. This study has two major topics: (i) macroscopic and microscopic
analysis of laser-diamond coupling, and (ii) nature of the laser-induced plasma evolution.
These two topics are closely linked to practical fabrication of patterned diamond
components by the innovative maskless patterning techniques. The laser-diamond
interaction is examined under various gas processing environments. The ablation rate of
the CVD diamond ﬁlm is measured, and linear and nonlinear models for the ablation
process are developed. The initial stage of the laser-diamond interaction is observed by
the atomic force microscope (AFM) and Raman spectroscope. To examine the
development of the surface morphology, in-situ observation is performed by
environmental scanning electron microscope (ESEM). Laser-induced plasma on the
CVD diamond ﬁlm is investigated by analytic instrumentations, such as laser-induced
breakdown spectroscopy (LIBS), and time-integrated plasma image capturing. The
excitation temperatures of the plasma are deduced by the Boltzmann-plot method.
Electron densities are calculated from the proportionality between the Stark effect on the

line broadening and the electron population. A maskless patterning system has been

designed and demonstrated patterning on the diamond ﬁlms. The results of this
investigation establish the great potential of CVD diamond ﬁlms for various applications,
such as semiconductor devices, sensors, optical windows and microelectromechanical

systems (MEMS).

To my wife and family

iv

ACKNOWLEDGMENTS

I would like to express my heartful thanks to Prof. K. Mukherjee for his guidance,
advice and ﬁnancial support throughout the duration of this research. I would like to
express my sincere gratitude to my dissertation committee members: Prof. K. N.
Subramanian, Prof. P. Kwon, and Prof. S. Flegler. I would like to thank all of my
colleagues in the High Energy Laser Processing Laboratory: Dr. Satya, Dr. Chen, Yiping

Hu, Hu Ning, Jim Cross, Matt Lonnstron, and Byron Chartier.

W

Chapter I. Intorduction ........................................................................................................ 1
Chapter II. Brief Review of Lasers and CVD Diamond Films ........................................... S
2.1. Lasers ........................................................................................................................... 5
2.1.1. Fundamentals of lasers .......................................................................................... 5
2.1.1-a. Lasing mechanism .......................................................................................... 6
2.1.1-b. Light ampliﬁcation in optical resonator ......................................................... 8
2.1.2. Characteristics of laser beam ................................................................................. 9
2.1.2-a. Spatial pattern of laser beam .......................................................................... 9
2.1.2-b. Power Density .............................................................................................. 10
2.1.2-c. Pulse repetition ............................................................................................. 11
2.1.3. Types of Lasers ................................................................................................... 12
2.1.3-a. Dye Lasers .................................................................................................... 12

2.1 .3-b. Semiconductor lasers ................................................................................... 15
2.1.3-c. Solid-state lasers ........................................................................................... 16
2.1.3-d. C02 lasers ..................................................................................................... 20
2.1.3-e. Excimer lasers .............................................................................................. 22

2.2. CVD diamond ﬁlm ..................................................................................................... 27
2.2.1. Growth of CVD diamond .................................................................................... 27
2.2.2. Properties of CVD diamond ................................................................................ 33
2.2.3 Applications for CVD diamond ........................................................................... 35
2.2.3-a. Coated tools .................................................................................................. 35
2.2.3-b. Heatsink ....................................................................................................... 36
2.2.3-c. Optical windows ........................................................................................... 36
2.2.3-d. Semiconductor devices ................................................................................ 37
2.2.3-e. Sensors and MEMS ...................................................................................... 39
Chapter III. Experimental .................................................................................................. 40
3.1. CVD Diamond Films ................................................................................................. 40
3.2. MP-I Maskless Patterning System ............................................................................. 44
3.2.1. Excimer laser ....................................................................................................... 44
3.2.2. Imaging optics ..................................................................................................... 47
3.2.3. Micro computer numerical control (micro-CNC) stage ...................................... 51

vi

Chapter IV. Laser Diamond Coupling .............................................................................. 54

4.1. Laser-Diamond Interaction ........................................................................................ 54
4.1.1. Excimer laser irradiation on CVD diamond ﬁlm ................................................ 54
4.1.2. Irradiation in ambient air ..................................................................................... 58
4.1.3. Irradiation in vacuum condition .......................................................................... 62
4.1.4. Irradiation in gas-streaming condition ................................................................ 65

4.2. Parameters of Laser-Diamond Coupling .................................................................... 71
4.2.1. Excimer laser ablation rate of CVD diamond ﬁlms ............................................ 71

4.2.1-a. Experimental setup for the rate measurements ............................................ 71
4.2. l-b. Ablation rate of CVD diamond ﬁlm ............................................................ 73
4.2.1-c. Modeling for the depth ablation ................................................................. 77
4.2. l-d. Prediction of the ablation depth ................................................................... 82
4.2.l-e. Veriﬁcation of the modeling ........................................................................ 84
4.2.2. Laser-diamond interaction ................................................................................... 87
4.2.2-a. Diamond to graphite phase transformation .................................................. 87
4.2.2-b. Evolution of surface morphology ................................................................ 94
4.2.2-c. Removal of graphite layer ............................................................................ 97

4.3. Chapter Summary ..................................................................................................... 101

Chapter V. Laser Induced Plasma on CVD Diamond Films ........................................... 104

5.1. Laser-Induced Breakdown Spectroscopy (LIBS) ................................................... 104
5.1.1. Introduction to LIBS ......................................................................................... 104

5.1 .l—a. Generation of laser-induced plasma ........................................................... 104
5.1.1-b. Characteristics of Laser-induced plasma ................................................... 106
5.1.2. LIBS instrumentation ........................................................................................ 109
5.1.3. Identiﬁcation of line emission spectra .............................................................. 113
5.1 .3-a. Identiﬁcation of carbon emission spectra .................................................. 115
5.1.3—b. Identiﬁcation of environmental gas breakdown ........................................ 120
5.1.4. Inﬂuence of laser irradiances on emission spectra ............................................ 126
5.1.5. Excitation temperature of the laser-induced plasma ......................................... 136
5.1.6. Electron density of the laser-induced plasma .................................................... 144
5.1.7. Physical and chemical interpretation of the emission spectra ........................... 148
5.1.7-a. C2 Swan bands ............................................................................................ 149
5.1.7-b. CN Violet bands ......................................................................................... 153

5.2. Images of Laser-Induced Plasma ............................................................................. 157
5.2.1. Interaction of laser-induced plasma .................................................................. 157
5.2.2. Image capturing of laser-induced plasma .......................................................... 159
5.2.3. Time-integrated images of laser-induced plasma .............................................. 162

5.2.3-a. Laser induced plasma on CVD diamond ................................................... 162
5.2.3-b. Effects of dynamic gas-streaming on plasma-material interaction ............ 169
5.3. Chapter Summary ..................................................................................................... 173

vii

Chapter VI. Fabrication of Micro-Components on CVD Diamond Films ...................... 176

6.1. Maskless Patterning on CVD Diamond Films ......................................................... 176
6.1.1. Maskless patterning versus lithography-based patterning ................................ 177
6.1.2. Maskless patterning in various gas processing conditions ................................ 182
6.1.3. Processing for complicated, and large patterns ................................................. 185
6.1.4. Fabrication of diamond lens by maskless patterning process ........................... 186
6.1.5. Contour patterning on CVD Diamond Films .................................................... 189

6.2. Chapter Summary ..................................................................................................... 192

Chapter VII. Conclusion ................................................................................................. 193

APPENDICES ................................................................................................................. 198

APPENDIX A ................................................................................................................. 199

APPENDD( B ................................................................................................................. 200

APPENDIX C ................................................................................................................. 213

APPENDIX D ................................................................................................................. 216

APPENDD( E .................................................................................................................. 218

APPENDD( F .................................................................................................................. 220

BIBLIOGRAPHY ........................................................................................................... 222

viii

LIST OF TABLES

Table 1. Major semiconductor lasers and their wavelengths [29] ..................................... 17
Table 2. Various types of common excimers and their wavelengths [33]. ...................... 23
Table 3. Comparison of material properties between CVD diamond and other materials
[3—5, 41]. .................................................................................................................... 33
Table 4. Processing parameters for the CVD diamond ﬁlms used in this study. ............. 43

Table 5. Speciﬁcations of the KrF excimer laser, Lambda PhysikO COMPex 301 . ......... 46
Table 6. Size of the apertures in the automatic aperture unit and resultant beam spot size
at the target. ............................................................................................................... 50
Table 7. Speciﬁcations for the components of the 5-motion-axes micro-CNC stage. ..... 53
Table 8. Measured processing parameters for the nonlinear ablation depth modeling. 82
Table 9. Measured processing parameters for the nonlinear ablation depth modeling. 85
Table 10. Molecular emission band systems for carbon and carbonitride [96, 100]. ..... 117
Table 11. Measured FWHM values for the M (nm) in various gas processing conditions
and laser irradiances (W/cmz). ................................................................................ 146

W—

Figure 1. Schematic illustration for lasing mechanism, absorption, spontaneous emission

and stimulated emission [31]. ..................................................................................... 6
Figure 2. Schematic illustration for the light ampliﬁcation in an optical resonator [29,

33] ................................................................................................................................ 8
Figure 3. Laser beam proﬁle by transverse electromagnetic mode (TEM); a) rectangular

symmetry, b) cylindrical symmetry [36] ................................................................... 10
Figure 4. Wavelength ranges of various types of lasers [29]. ........................................... 12
Figure 5. Schematic diagram for energy level of a typical laser dye, showing both the

singlet and triplet states [29]. .................................................................................... 13
Figure 6. Schematic illustration of fundamental lasing mechanism in a semiconductor

laser [29, 40] .............................................................................................................. 15
Figure 7. Schematic diagram for energy level of the three-level ruby laser [29]. ........... 17

Figure 8. Schematic diagram for energy level of the four-level Nd:YAG laser [29]. ..... 19
Figure 9. Lasing mechanism of C02 laser, a) vibrational modes of C02 molecule, and b)

laser transitions among vibrational levels of C02 laser [29] ..................................... 21
Figure 10. Lasing mechanism of KrF excimer laser. ........................................................ 24
Figure 11. Construction of a typical excimer laser showing optical resonator of electron

beam discharged KrF excimer laser. ......................................................................... 25
Figure 12. Three general types of inorganic carbon structures; a) graphite, b) diamond,

and c) Buckyball ........................................................................................................ 28

Figure 13. Schematic diagram for the chemical vapor deposition of diamond [2]. ......... 29

Figure 14. Schematic illustration for the carbon phase diagram, and fabrication regions
for synthetic diamonds. The CVD diamond exists metastably in the graphite region
[3]. ............................................................................................................................. 30

Figure 15. Geometry of hydrogen terminated (100), (110), and (111) plane of a diamond
lattice, a) (111) plane, b) (110) plane, c) (100) plane, d) reconstructed (100) plane.
Large and dark circles represents carbon atoms, and small and light circles

represents hydrogen atoms [2]. ................................................................................. 32
Figure 16. Schematic diagram for the 7-inch microwave cavity plasma reactor (MCPR7)

at Michigan State University [43]. ............................................................................ 41
Figure 17. Hetero-epitaxially grown diamond ﬁlms on 2-inch-diameter and 3-inch-

diameter single crystal silicon wafers. ...................................................................... 42

Figure 18. Cross section of free standing diamond ﬁlm (ST204) showing the rough ﬁlm
surface of diamond-growth side (upper surface), and the ﬂat surface of the substrate

side (lower surface). .................................................................................................. 43
Figure 19. 3) Overview of the MP-I maskless patterning system, designed for this
research, and b) the schematic diagram of the MP-I system ..................................... 45

Figure 20. Beam energy proﬁle of rectangular beam (13x30 mmz) from the KrF excimer
laser showing a Gaussian proﬁle in its vertical section and ﬂat-top proﬁle in its
horizontal section [60] ............................................................................................... 46

Figure 21. Construction of the laser imaging system according to the thin lens principle.
................................................................................................................................... 47
Figure 22. Illustration for the components in the imaging optics in the MP—I system; a)
schematic diagram for the imaging optics, b) beam path diagram for the imaging
optics, c) automatic aperture unit and beam shutter, and (1) gas delivery unit for the
dynamic gas streaming. (these units were all designed and built for this research.) 49
Figure 23. Schematic diagram showing offset of the direction of the dynamic gas-
streaming nozzle ........................................................................................................ 50
Figure 24. 5-motion-axes micro-CNC stage in the MP-I system; a) schematic diagram, b)
front view, and c) side view. (The systems, and subsystem shown in these ﬁgures,

were designed and built for this research.) ................................................................ 52
Figure 25. Schematic diagram of the excimer laser setup for the laser-diamond
interaction. ................................................................................................................. 55
Figure 26. Surface morphology of as-synthesized CVD diamond ﬁlm subjected the laser-
diamond interaction. .................................................................................................. 56
Figure 27. The schematic diagram showing irradiation conditions in; a) the ambient air,
b) the vacuum condition, and c) the gas-streaming condition ................................... 57

Figure 28. SEM micrographs showing excimer laser irradiation in the ambient air; a) the
irradiation spot and surrounding with distinctive PAZ marked by 1, 2, and 3, b) the
irradiation spot, c) highly tilted (75°) image for the irradiation spot, a-l) magniﬁed
view of zone 1 from the ﬁgure a, a-2) magniﬁed view of zone 2 from the ﬁgure a, a-

3) magniﬁed view of zone 3 from the ﬁgure a. ......................................................... 60
Figure 29. Edge of the irradiation spot in the ambient air showing the radial-symmetric
ejection and damage near the edges. ......................................................................... 61

Figure 30. SEM micrographs showing excimer laser irradiation in the vacuum condition;
a) the irradiation spot and surrounding, b) the irradiation spot with distinctive zones
marked by 1, 2, and 3, c) highly tilted (75°) image for the irradiation spot, b-l)
magniﬁed view of zone 1 from the ﬁgure b, b-2) magniﬁed view of zone 2 from the

ﬁgure b, b-3) magniﬁed view of zone 3 from the ﬁgure b ........................................ 63
Figure 31. Near spot edge area showing the plasma affected zone in the vacuum

condition. ................................................................................................................... 64
Figure 32. Plasma affected zone in the vacuum condition showing the formation of the

debris droplets. .......................................................................................................... 65

Figure 33. SEM micrographs showing excimer laser irradiation in the argon gas-
streaming condition, a) the irradiation spot and surrounding, b) the irradiation spot
with areas marked by l, 2, and 3, arrows indicate gas stream direction, c) highly
tilted (75°) image for the irradiation spot, b-l) magniﬁed view of area 1 from the
ﬁgure b, b-2) magniﬁed view of area 2 from the ﬁgure b, b-3) magniﬁed view of

area 3 from the ﬁgure b. ............................................................................................ 67
Figure 34. Edge of the irradiation spot showing ablation-sectioned diamond crystals in

the argon gas streaming condition ............................................................................. 68
Figure 35. Light deposition of the ablation-debris on the edges and corners of the

diamond crystal in the argon gas streaming condition. ............................................. 68

Figure 36. Surface topographies of the irradiation spots of the diamond ﬁlm in the
different processing environments; a) ambient air, b) vacuum condition, and 0)

xi

argon gas-streaming condition. The topographies were taken by a confocal laser
scanning microscopy. ................................................................................................ 69
Figure 37. Schematic diagram of the excimer laser setup for the ablation measurements.
................................................................................................................................... 72
Figure 38. Depth proﬁle measurements of the irradiation spot by the confocal laser
scanning microscope; a) confocal image of the irradiation spot, b) linear depth
proﬁle across the spot from the inset b in the ﬁgure a, and c) high-resolution linear

proﬁle near the spot edge from the inset c in the ﬁgure a. ........................................ 74
Figure 39. Topographic depth proﬁle of the irradiation spot by optical z-sectioning of the
surface topography. ................................................................................................... 75
Figure 40. Ablation depth as a function of the number of laser pulses on the CVD
diamond ﬁlm. ............................................................................................................ 75
Figure 41. Ablation depth as a function of the laser irradiance on the CVD diamond ﬁlm.
................................................................................................................................... 76
Figure 42. Schematic diagram for the laser irradiation with divergent laser beam. ......... 78
Figure 43. Ablation depth d as a function of the number of laser pulses n according to the
Equation 17. .............................................................................................................. 81

Figure 44. Modeling of the ablation depth as a linear function of the number of the laser
pulses, and as a nonlinear function of the number of the laser pulses (at the initial

laser irradiance 6x108 W/cmz). ................................................................................. 83
Figure 45. Ablation depth as a function of the number of laser pulses on the thick
diamond ﬁlm. ............................................................................................................ 86

Figure 46. Extinction of the diamond Raman spectrum (1332 cm") by the excimer laser
irradiation; a) before the laser irradiation, b) after the laser irradiation, and c) Raman

spectrum. ................................................................................................................... 89
Figure 47. AFM (Tappingmode’) observation on the evolution of surface morphology by
the excimer laser irradiation. ..................................................................................... 91
Figure 48. AFM (TappingmodeQ) observation, in sub-micron scale, on the evolution of
surface morphology by the excimer laser irradiation. ............................................... 92
Figure 49. Observation of the Raman spectrum on the excimer laser irradiated diamond
surfaces. ..................................................................................................................... 93

Figure 50. ESEM in-situ observation on the evolution of the surface morphology of the
laser irradiated diamond surface; a) 0 pulse, b) 5 pulses, c) 20 pulses, d) 50 pulses, e)
100 pulses, and f) 200 pulses. The arrows indicate the same position throughout the
observation. ............................................................................................................... 95

Figure 51. Roughness reduction of the polycrystalline diamond surface by the excimer
laser irradiation; a) before the laser irradiation, and b) after 200 laser pulses at 6x108

W/cmz. ....................................................................................................................... 96
Figure 52. Formation of the self-sustaining graphite micro-layer upon the excimer laser
irradiation by 200 pulses of irradiation at 6x108 W/cm2 ........................................... 97

Figure 53. Edges of the irradiation spots showing the carbon debris deposited by the
irradiation (left column) and cleaned edges by the removal of the deposition (right
column); a-l) ambient air - as irradiated, a-2) ambient air - after the cleaning; b-l)
helium streaming - as irradiated, b—2) helium streaming - after the cleaning; c-l)
argon streaming - as irradiated, c-2) argon streaming - after the cleaning ................ 99

xii

Figure 54. Damaged diamond crystals around the spot edge from the laser irradiation in
the ambient air; a) the damaged spot edge, the arrows indicate the damaged area, b)
magniﬁed view of the damaged area, indicated by the arrows. .............................. 100

Figure 55. Schematic diagram for the temporal evolution of the laser-induced plasma,
illustrating various regimes of the emission spectra. 25 ns laser pulse duration of
KrF excimer laser and irradiance over ablation threshold were assumed [18, 74, 82,

83, 88] ...................................................................................................................... 107
Figure 56. Schematic diagram of the LIBS setup for the acquisition of the laser-induced
plasma on the CVD diamond ﬁlm. ......................................................................... 110

Figure 57. Indexing map for the emission spectra on the CVD diamond ﬁlm, a) indexing
map for the atomic emission spectra, b) indexing map for the molecular spectra. 114
Figure 58. Identiﬁcation of molecular carbon emission spectra from the LIBS on CVD

diamond ﬁlm. .......................................................................................................... 116
Figure 59. Comparison of dominant molecular emission bands, CN violet and C2 Swan,
among the gas processing conditions. ..................................................................... 118
Figure 60. Identiﬁcation of atomic carbon emission spectra from the LIBS on CVD
diamond ﬁlm. .......................................................................................................... 119
Figure 61. Identiﬁcation of molecular environmental-gas breakdown from the LIBS on
CVD diamond ﬁlm .................................................................................................. 121
Figure 62. Identiﬁcation of atomic environmental-gas breakdown from the LIBS on CVD
diamond ﬁlm ........................................................................................................... 123
Figure 63. Identiﬁed line emission spectra by LIBS on the CVD diamond ﬁlm in the
wavelength region 350 nm ~ 600 nm. ..................................................................... 124
Figure 64. Identiﬁed line emission spectra by LIBS on the CVD diamond ﬁlm in the
wavelength region 550 nm ~ 825 nm. ..................................................................... 125
Figure 65. Laser-induced plasma emission spectra on the diamond ﬁlm in ambient air as
a function of the laser irradiance. ............................................................................ 127
Figure 66. Laser-induced plasma emission spectra on the diamond ﬁlm in argon gas-
streaming as a function of the laser irradiance. ....................................................... 129
Figure 67. Laser-induced plasma emission spectra on the diamond ﬁlm in helium gas-
streaming as a function of the laser irradiance. ....................................................... 130

Figure 68. In the ambient air, the intensities of the emission spectra and the continuum
background are plotted as a function of the laser irradiance, a) C2 Swan band, b) CN
Violet band, and C) CH. Corresponding ratios of the emission spectra to the
background are shown in, a-l) C2 Swan band, b-l) CN Violet band, and 0-1) CH.
The guide lines are arbitrarily drawn to show trends of the data. ........................... 131

Figure 69. In the helium gas-streaming, the intensities of the emission spectra and the
continuum background are plotted as a function of the laser irradiance, a) C2 Swan
band, b) CN Violet band, and C) CH. Corresponding ratios of the emission spectra
to the background are shown in, a-l) C2 Swan band, b-l) CN Violet band, and c-l)
C11. The guide lines are arbitrarily drawn to show trends of the data. ................... 132

Figure 70. In the argon gas-streaming, the intensities of the emission spectra and the
continuum background are plotted as a function of the laser irradiance, a) C2 Swan
band, b) CN Violet band, and C) CH. Corresponding ratios of the emission spectra
to the background are shown in, a—l) C2 Swan band, b-l) CN Violet band, and c-l)
CH. The guide lines are arbitrarily drawn to show trends of the data. ................... 133

xiii

Figure 71. Modeling of the emission intensity of the CVD diamond as a function of the
laser irradiance for the various gas processing conditions; a) C2 Swan band at 516.52
nm, b) CN Violet band at 388.34 nm, and C) CH 567.81 nm. The displayed values
of irradiance coefﬁcient a were obtained by lower and upper boundary values of the

emission intensities and laser irradiances ................................................................ 137
Figure 72. Emission spectra of the C2 Swan bands in various vibrational transition levels
used for the temperature measurements. ................................................................. 141

Figure 73. ln(l‘lvw) in various vibrational levels as a function of G(v) in various laser
irradiances in the gas processing conditions, a) ambient air, b) helium gas

processing, and c) argon gas processing. ................................................................ 142
Figure 74. Excitation temperature of the C2 Swan bands in various gas processing

conditions as a function of laser irradiance. ............................................................ 143
Figure 75. Electron density in various gas processing conditions as a function of the laser

irradiance. ................................................................................................................ 147

Figure 76. Comparison of ablation debris around the irradiation spots among the gas
processing conditions; (a) and (a-l) ambient air, (b) and (b-l) helium gas-streaming,

, and (c) and (c-l) argon gas-streaming ..................................................................... 155
Figure 77. Interaction of laser-induced plasma to the surrounding [23, 27, 78]. ............ 158
Figure 78. Schematic diagram for the time-integrated image capturing of laser-induced
plasma on the CVD diamond ﬁlm. ......................................................................... 160
Figure 79. Plots showing wavelength pass ranges for the optical ﬁlters; a) band pass ﬁlter
BP400, and b) long pass ﬁlter LP525. .................................................................... 161

Figure 80. Example of the synchronized capturing (100 us time frame acquisition for the
10 Hz irradiation) of the time-integrated plasma images. Each image is captured by
100 us integrated-acquisition from a single pulse of the laser irradiation. ............. 163
Figure 81. Time-integrated image of laser-induced plasma on the CVD diamond ﬁlm in
ambient air; a) unﬁltered image, b) image captured with BP400 ﬁlter, and c) image
captured with LP525 ﬁlter, the arrow indicates the ejection of a large particle. 164
Figure 82. Time-integrated image of laser-induced plasma on the CVD diamond ﬁlm in
the helium gas-streaming; a) unﬁltered image, b) image captured with BP400 ﬁlter,
and c) image captured with LP525 ﬁlter. ................................................................ 166
Figure 83. Time-integrated image of laser-induced plasma on the CVD diamond ﬁlm in
the helium gas-streaming; a) unﬁltered image, b) image captured with BP400 ﬁlter,
and c) image captured with LP525 ﬁlter. ................................................................ 167
Figure 84. Time-integrated images of laser-induced plasma on the polyester resin; a)
image captured in ambient air, arrows indicate the convection stream of plasma near
the target surface, b) image captured in argon gas-streaming, and c) image captured
in helium gas-streaming, no optical ﬁlter was used for all captured images. ......... 170
Figure 85. Laser irradiation on a leuco-dye coated paper for thermal detection around the
irradiation spot; a) irradiation in the ambient air, indicating the temperature increase
around the irradiation spot, b) irradiation in argon gas-streaming, and c) irradiation

in helium gas-streaming. ......................................................................................... 171
Figure 86. Comparison of the processing steps between; a) the maskless ablation
technique, and b) the lithography-based patterning ................................................ 178

Figure 87. Diamond growth on the diamond-seeded photoresist layer showing lateral
growth; a) the CVD diamond sensor (thermistor) by the lithography-based

xiv

patterning, b) resolution on its edge, c) lateral growth in the reactor and d)

illustration for the diamond growth ......................................................................... 179
Figure 88. Drawing scheme, i.e., translation scheme for the micro-CNC stage, for the
maskless patterning on CVD diamond ﬁlm. ........................................................... 180

Figure 89. Isolated cell-pattern on a CVD diamond ﬁlm by the excimer laser maskless
patterning process, a) the isolated cell-pattem, b) magniﬁed view on the cell edge.
................................................................................................................................. 181

Figure 90. Maskless ablation process for the isolated-cell pattern in the various gas
processing conditions; a) ambient air, b) helium gas streaming, and c) argon gas
streaming. The arrows indicate the positions for the detection of Raman spectrum in

Figure 91. ................................................................................................................ 183
Figure 91. Raman spectra on the isolated-cell patterns, processed in the various gas
processing conditions. ............................................................................................. 184

Figure 92. A magniﬁed view of a complicated patterning on the diamond ﬁlm showing
the emblem of the Michigan State Univeristy, the Spartan helmet and the letters,

MSU. ....................................................................................................................... 185
Figure 93. Fabrication of three isolated-cell patterning on the diamond ﬁlm by the
maskless ablation technique. ................................................................................... 186

Figure 94. Fabrication of the CVD diamond lens from the thick ﬁlm micromachining by
the maskless patterning system; a) 3.5 mm diameter diamond lens cut from the
freestanding diamond ﬁlm, b) the diamond lens, c) cutting edge of the lens. ........ 188

Figure 95. Square pattemed-cut diamond lens which is placed over the laser cut hole. 189

Figure 96. Schematic diagram for the patterning of the circular contour track, using
rotation and tilt stages. ............................................................................................ 191

Figure 97. Circular contour-track on the freestanding diamond ﬁlm by using rotation and
tilt stages; a) overview of the circular contour-track, and b) magniﬁed view of the
edge area .................................................................................................................. 191

LIST OF ABBREVIATIONS

AFM ............................................................................................ Atomic Force Microscope
CCD ................................................................................................. Charge Coupled Device
CN C ........................................................................................ Computer Numerical Control
CI‘E ................................................................................ Coefﬁcient of Thermal Expansion
CVD ......................................................................................... Chemical Vapor Deposition
ESEM .......................................................... Environmental Scanning Electron Microscope
FWHM ....................................................................................... Full Width Half Maximum
HELP ..................................................................................... High Energy Laser Processing
LIBS ...................................................................... Laser Induced Breakdown Spectroscopy
LSM ........................................................................................... Laser Scanning Microscope
LTE ................................................................................ Local Thermodynamic Equilibrium
MCPR7 ............................................................... 7-inch Microwave Cavity Plasma Reactor
MEMS .............................................................................. Microelectromechanical Systems
NA ......................................................................................................... Numerical Aperture
NIST ............................................................ National Institute of Standard and Technology
PAZ .................................................................................................... Plasma Affected Zone
PPS ............................................................................................................ Pulse Per Second
SEM ...................................................................................... Scanning Electron Microscopy
TEA ................................................................. Transversely Excited Atmospheric Pressure
TEM ............................................................................... Transverse Electromagnetic Mode

Chapter I

INTRODUCTION

Rapidly growing demands on electronic materials seek high performance ﬁlms.
CVD diamond ﬁlms inherit superior mechanical properties of a natural diamond, such as
high hardness and moduli, wear resistance, and low friction coefﬁcient. Also, potential
of diamond ﬁlms for electronic devices has been widely recognized by virtue of their
largest intrinsic band gap, lowest dielectric constant, predicted high carrier mobility, high
break down ﬁelds and thermal conductivity [1-6].

The excellent mechanical and electrical properties make chemical vapor deposited
(CVD) diamond ﬁlms uniquely qualiﬁed for the applications, such as integrated circuits,
sensors, optical windows and microelectromechanical systems (MEMS) [7-10]. To
utilize the excellent properties of the diamond ﬁlms in the applications, micromachining
and patterning of diamond ﬁlms are primarily required [11, 12]. For ultra-hard ﬁlm
materials, such as CVD diamond, conventional machining and lithography-based
patterning are difﬁcult due to the high wear resistance and the chemical inertness. Pulsed
laser ablation has been used for vaporizing ﬁlm materials to make patterned structures
and micro-components. The laser ablation is a direct process that requires only proper
arrangement of optics to control the laser beam [13]. By subjecting a ﬁlm surface to
pulsed laser irradiation, a thin layer of the target surface is instantaneously ablated,
creating micro patterns and/or structures on the surface. CVD diamond ﬁlms have been

processed by various types of pulsed lasers for this purpose [14-24]. Nanosecond-pulsed,

excimer lasers have been applied for surface modiﬁcations of CVD diamond ﬁlms [14-
16, 18-20]. In these investigations, the excimer lasers have shown their capabilities in
polishing, etching, and patterning of the diamond ﬁlms. Reduced surface roughness,
improved optical transmittance, and patterned structures were reported from these
applications. However, the processes have exhibited damage, such as transformed
surface layers, and spoiled spot edges. These drawbacks have been obstacles to the
application of the nanosecond-pulsed excimer lasers to high-resolution micromachining.
Recently, femtosecond pulsed UV lasers have been introduced to overcome the
drawbacks [2124]. By utilizing the ultrashort-pulsed irradiation on the CVD diamond
ﬁlms, the ablation process could show some improvements as compared to that of the
nanosecond pulsed laser process. Even though the ultrashort laser ablation showed
improvements on surface ﬁnish and purity of the irradiated diamond ﬁlms, it was not
completely successful to avoid the damage, such as rippled surfaces, and blurred
interfaces.

In the ablation processes, plasma formation is inevitable due to the characteristics
of short or ultrashort pulsed laser irradiation. Even though the pulsed laser-material
interaction is limited to nanoseconds to femtoseconds ranges, the plasma extends for far
longer times than the laser pulse duration. In studies of ultrafast imaging of nanosecond
pulsed laser ablation [13, 25-28], it was visualized that the formation and expansion of
plasma, induced by ablative material ejection, extended up to tens of microseconds.
Propagation of shock waves was also observed due to the expansion of the high
temperature plasma, which exists long enough to transfer heat to the target surface. In

these respects, the formation and expansion of the plasma give rise to the damage, such

as plasma material ejection and deposition, spoiled interface, recast layers, and rippled
surfaces. The plasma-induced damage has been an obstruction to achieve high-resolution
micromachining and patterning of diamond ﬁlms.

The high-resolution micromachining and patterning can be achieved by
maximized acquisition of accuracy and controllability of the laser ablation process. The
accuracy and controllability are directly related to plasma-diamond interaction and laser-
diamond coupling, respectively. This study aims to investigate plasma-diamond
interaction and laser-diamond coupling to improve the practical aspects of
micromachining and patterning. The study of plasma-diamond interaction is mainly
focused on novel approaches to minimize the plasma-induced damage. In this study,
CVD diamond ﬁlms were subject to various gas processing environments, such as
ambient air, vacuum and gas-steaming condition. Evolution of plasma was signiﬁcantly
affected by these conditions, which alter the ionization potential of the processing
environment. Various instrumentations, including the time-integrated plasma image
capturing and the laser-induced breakdown spectroscopy (LIBS) were performed to
analyze the laser-induced plasma. Observed damage were dependant on behavior of the
plasma in the different processing environments. The dynamic gas—streaming proved that
proper dissipation of the plasma led to precisely irradiated surfaces, which were almost
free from damage. Emphases of the plasma study are to achieve maximum dissipation of
the plasma and proper quenching of the target surface.

Laser-diamond coupling was investigated by macroscopic and microscopic
analyses to characterize intrinsic properties of CVD diamond ﬁlms. Most of the

polycrystalline diamond ﬁlms retain high surface roughness due to the nature of CVD

processing. In the microscopic analyses of the initial laser-diamond coupling, an atomic
force microscope (AFM) was used to examine the subjected diamond ﬁlms.
Macroscopic changes of the surface morphologies were also examined by the in-situ
observation upon the laser irradiation. The ablation rate of the CVD diamond ﬁlm was
measured to model the laser ablation process on the CVD diamond ﬁlm.

For the laser ablation process of diamond ﬁlms, applied and fundamental
investigations are required to overcome the current barriers. Subsequently, maximum
accuracy and controllability of the ablation process can produce the precisely
micromachined, and patterned diamond ﬁlms. In these respects, this study aims for two
major goals; i) macroscopic and microscopic analysis of laser-diamond coupling, and ii)
analysis on the laser-induced plasma and its interaction to surrounding. The fundamental
aspects in this study were linked to practical fabrication of patterned diamond
components by the innovative maskless patterning technique. The maskless patterning
technique employs pulsed irradiation of focused laser beam on a target material, which is
translated to the programmed positions by the micro-CNC. Along with its advantages of
a simple setup and a direct process, the maskless process makes a rapid prototyping
possible for patterns on ultra-hard ﬁlm materials. The maskless patterning introduces
CVD diamond ﬁlms to new area of sensors, optical windows, integrated circuits and
MEMS, where extreme tolerance of a material is required. Diamond ﬁlms of unmatched
materials properties will drastically increase performance in various potential

applications.

Chapter II

A BRIEF REVIEW OF LASERS AND CVD DIAMOND FILMS

2.1. Lasers

Lasers are extensively utilized in advanced materials processing. Therefore, an
understanding of the basic laser principles, and their operation is essential for selecting
right types of lasers for the related materials processing. In this section, basic principles

of laser operation, and related types of lasers are brieﬂy reviewed.

2.1.1. Fundamentals of lasers

The word laser stands for light ampliﬁcation by stimulated emission of radiation.
Laser makes use of processes that amplify light signals. Three fundamental phenomena
such as absorption, spontaneous emission, and stimulated emission are related to the light
ampliﬁcation [29, 30].

Consider an atom with two energy levels, an upper level E2, and a lower level E],
as shown in Figure 1. The atom is initially lying in the lower level E2 in ground state.
When this atom is irradiated by an incident radiation with photon energy equal to or

larger than the energy difference of the two levels (E2 — E1), the atom is excited to the

upper level E2. This is the energy absorption process. When the atom returns form E2 to
the ground state E 2, the atom releases its excess energy by a radiative process; giving rise

to spontaneous emission.

 

 

 

 

SPONTANEOUS
amwmu
E; (1 n2
hv hv 2hv
El ummwnmv n’ ”WWUWH’
emﬂmm

Figure 1. Schematic illustration for lasing mechanism, absorption, spontaneous emission
and stimulated emission [31].

Spontaneous emission occurs when the excited atom spontaneously returns to the ground
state by releasing the corresponding energy difference hv. It can be expressed by the
relationship [29, 30]:

E2 - E‘ = h V Equation 1
where h is Plank’s constant, and V is frequency. Stimulated emission occurs when
photons from the spontaneous emission trigger atoms in the excited state to emit
radiation. Such stimulated emission has the monochromatic wavelength. This stimulated
emission is constructively ampliﬁed to produce the laser beam. The light ampliﬁcation is
done by optical feedback, in which a set of mirrors feed the light back into the ampliﬁer

for continued growth of the developing laser beam.

2.1.1 -a. Lasing mechanism

A laser is an optical transducer that converts input energy to intensively ordered

light emission. The laser ampliﬁes light and produces a highly directional beam that

typically has a monochromatic wavelength. The laser consists of three major parts, an
energy source for pumping, a lasing medium, and an optical resonator [29, 32].

In Figure l, the population of atoms in the energy states E1 and E2 can be
expressed by n, and n2, respectively. For a system in thermal equilibrium, the ratio of

populations is given by the Boltzmann relationship [29, 30]:

n2 El - E2 .
_ = ex __ Equation 2
"1 P( kT )

where k is Boltzmann constant, and T is the absolute temperature of the material.
According to the Boltzmann equilibrium, a larger population exists in a lower energy
state, that is, n, > n2. The population inversion is the nonequilibrium state where the
population of higher energy state is greater than that of the lower energy state, that is n2 >
n). The population inversion is the basic requirement for lasing mechanism. The lasing
occurs when the achieved population inversion is high enough to overcome energy losses
inside the resonator. An external energy source is needed to buildup a population of
atoms or molecules in excited states. This is called the ‘pumping.’ Optical pumping and
electrical pumping are the basic pumping methods for lasers. Generally, gas lasers use
electrical discharge, and solid-state lasers, such as NszAG and ruby lasers, use the
energy of ﬂash lamps. For the optical pumping, continuous lasers use are lamps and

tungsten lamps, while pulsed lasers usually use ﬂash lamps.

OPTICAL RESONATOR

 

 
   
 

LASER BEAM

 
  

4
, .
Kw

’ ..u

PARTIALLY
REFLECTING TRANSMITTING
MIRROR MIRROR

Figure 2. Schematic illustration for the light ampliﬁcation in an optical resonator [29,
33].

2.1.I-b. Light ampliﬁcation in Optical resonator

A schematic illustration for the typical optical resonator is shown in Figure 2.
The optical resonator contains a lasing medium, which is closed off with two mirrors, one
is fully reﬂecting and the other is partially reﬂecting. The lasing medium is usually a
crystal or rod for solid lasers, and long gas-containing tube for gas lasers. When an
optically or electronically pumped lasing medium emits photons by spontaneous
emission, these emitted photons stimulate emission from other excited atoms or
molecules in the lasing medium. The stimulated emission, which occurs in the axis
between the two mirrors, is ampliﬁed by multiple passages of photons through the
medium. In this condition, photons are optically resonating in the cavity for the
ampliﬁcation. A laser beam is generated from the optical resonator when the
ampliﬁcation of resonating photons reaches enough intensity to overcome the threshold

of the partially transmitting mirror [29, 30, 32, 33].

2.1.2. Characteristics of laser beam

2.1 .2-a. Spatial pattern of laser beam

Transverse and longitudinal modes are the two distinct types of beam modes for
the optical resonators [29, 34, 35]. Transverse modes describe the cross-sectional proﬁle
of the beam, and longitudinal modes correspond to different resonance along the length
of the optical resonator. The spatial proﬁle of laser beam is affected by design of the
optical resonator, which includes geometry of optics, and the gain in the resonator cavity.
Impurities in the lasing medium, and the pumping power affect the mode structure of the
beam as well.

The beam proﬁle is normally characterized by its transverse electromagnetic
mode (TEM). The TEM is expressed by the notation TEM”, where the subscripts m and
n represent the number of nodes/nulls in directions orthogonal to the beam propagation
[29, 34-36]. Figure 3 shows the intensity distribution in the plane, perpendicular to the
plane in which the mode distribution lies. The transverse modes can be represented in
either Cartesian coordinates or in cylindrical coordinates. For rectangular symmetry in
Figure 3a, the notation TEM,“ is interpreted as the number of nulls that occur in the
spatial pattern in each of the two orthogonal directions, transverse to the direction of the
beam propagation. For cylindrical symmetry in Figure 3b, the integer m indicates the
number of nulls in radial direction, and n indicates half the number of nulls in an
azimuthal direction. The modes marked by asterisk are linear superposition of two modes

operating simultaneously 90° out of phase.

10

00 1o 20 30

Q g ‘0‘ .. .. '-
-::: -
' ' ‘I‘ :0 O. ;
11 21 33 04
(a)
00 01* 1o 11 20

- Q D s'o §‘%

01 02 03 04
(b)

Figure 3. Laser beam proﬁle by transverse electromagnetic mode (TEM); a) rectangular
symmetry, b) cylindrical symmetry [36].

Generally, gas lasers have well deﬁned rectangular or cylindrical symmetries in the cross
section. However, spatial patterns of solid lasers, such as ruby and Nd:YAG, can not be
described in simple mathematical terms, because of complicated spatial patterns [32].

This complexity in spatial patterns is caused from inevitable imperfections within the

lasing media of the solid crystals.

2.1.2-b. Power Dem

Depending on the average power of the laser, a typical pulsed laser produces 1015
to 1030 photons per second. In contrast a typical hollow cathode lamp produces 106 to 108

photons per second at a single wavelength [30]. The power of a laser, even with

11

moderate power in a few rnilliwatts, is orders of magnitude greater than that of the
brightest conventional light source. The solid-state lasers recently have reached an
average maximum of power of about 1 kW. Substantially high powers are obtainable
from gas laser, which is suitable for industrial applications. Commercial continuous-
wave lasers have typical power range from less than a milliwatt to tens of kilowatts.
Comparable average power range is available for pulsed lasers as well. Using focusing
optics, the power of a laser beam can be concentrated into a very small spot. The focused
laser beam increases power density, which is usually expressed by the laser irradiance
(W/cmz). The irradiance is the measure of the transferred laser power per unit cross-
sectional area of the laser spot. Pulsed lasers, with the laser irradiance in excess of 1012
W/cmz, are now available from relatively small systems [37]. Laser irradiation, with very
high power density, induces an instantaneous evaporation of the solid. This laser ablation

is essential for the laser spectroscopy, laser vapor deposition, and micromachining [38].

2.1 .2-c. Pplge repetition

The maximum pulse repetition rates vary widely for types of lasers. Ruby and
Ndelass lasers can generate at most a few tens of pulses per second (pps). The excimer
lasers have wide range of pulse repetition rate up to a thousand pulses per second. Pulse
repetition rate, duration, and peak power can also be adjusted by a variety of laser
accessories such as Q-switches, mode lockers, and cavity dumpers. The temporal width
of a pulsed laser is important for laser-based micromachining. Nanosecond (10‘9 sec),
picosecond (10'12 s), and femtosecond (10"5 s) pulses are commercially available for

various applications [29, 33, 37].

12

HF Diode Xe Cl
. H

 

 

CO Ar
Ruby N2
He-Ne KrF
Soft-X-Ray
FIR Lasers Nd:YAG He-Cd Lasers
o————. <————>
602 He-Ne Organic Dye
112N203 ATF
Far Infrared infrared Visible Ultraviolet Soft X-Raye
J l l I‘Mi l l 1
30pm 10pm 3pm 1pm 300nm 100nm 30nm 10nm

<——-——-2.

—— ENERGY (“7.9) .....

 

Figure 4. Wavelength ranges of various types of lasers [29].

2.1.3. Types of Lasers

Lasers are generally categorized by lasing medium, and pumpingimethods. Such
lasers span the wavelength range from infrared to ultraviolet, as shown in Figure 4.
According to the general classiﬁcation, lasers are grouped as dye, semiconductor, solid-

state, and gas (C02 and excimer) lasers [29, 31, 33]. These lasers are brieﬂy reviewed in

this section.

2.1 .3-a. de Lasers

Dye lasers are usually excited by lamps or pulsed lasers for pulsed operation, or

by continuous lasers for continuous-wave radiation.

13

 

 

  
 

 

 

 

 

 

i \ ,1’
Fast decay : L 7
31 i
I .
Singlet ' Triplet
5 absorption S1—>T, conversion / absorption
1
Singlet I
3 emission b’Biy‘fL ”
ngeiF‘s g
l 2:57 T1
! é§,/’
SO ’539‘1 ’i’
:
Fast decay ) l
j (
Distance Distance

Figure 5. Schematic diagram for energy level of a typical laser dye, showing both the
singlet and triplet states [29].

The lasing mechanism of liquid-state dye laser is based on ﬂuorescent transitions in large
organic molecules in solution. The energy levels associated with organic dyes,
suspended in solvents, are shown Figure 5. There are two sets of energy levels in which
excitation and decay can occur [29]. These are singlet and the triplet manifolds, which
refer to S and T in Figure 5, respectively. The various electronic energy levels of So, S],
T, and T2 are associated with vibrational and rotational energy levels in the case of
simpler molecules. When the dye laser is externally pumped, excitation occurs from the
ground state Soto the excited state S I. If the excitation or pump energy occurs over broad
spectra, all of the vibrational states of S 1 can be populated. However, decay of the
rotational and vibrational levels in S1 occurs very rapidly to the lowest excited level in S 2.
The accumulation of population at the lowest level of S 1 creates the population inversion

between S; and So. The stimulated emission occurs by the slow decay to So, which is the

14

radiative transition creating laser. The triplet states essentially form separate molecules
that are only weakly coupled to the singlet states by weak radiative or collisional
interactions. Since T1 lies below S1, some of the population in S; can decay to T 2. The
population will then accumulate in T2, since the weak decay from T1 to So occurs in
longer time. Thus, when excessive population moves from singlet state S, to the triplet
state T1, the triplet state absorption of a dye can reduce or cancel the laser gain produced
in the singlets. Due to this fact, the optical resonator mechanically ﬂows the dyes in the
excitation region to physically remove the triplet state population, and to enhance laser
output from the singlet system. Depending on the dye used, the output wavelength of the
liquid-state dye laser can be tuned from the near-ultraviolet through the near-infrared
range, typically 340 nm to 1 um. The use of frequency-doubling crystals can extend
emission further into the near-ultraviolet. The active medium in a dye laser is a
ﬂuorescent organic dye dissolved in a liquid solvent. Over 200 dyes are available for
lasing medium [39]. Dyes are large ﬂuorescence molecules containing conjugated
double bonds with multiple rings, and have complex spectra. The most widely used
example is rhodarnine 6G, which has wavelength output near 580 nm [39]. Major
drawback of the dye lasers is photo-degradation of the dye, due to the external light or
laser pumping. Rhodamine 6G has a lifetime of about 2000 watt hours, and many other
long-wavelength dyes have lifetimes of several hundred watt hours. Dyes are usually
dissolved in organic solvents such as methanol, and dimethylsulfoxide. Solvents of the
liquid-state dye also affect both optical properties and degradation of laser dyes. In order

to be useful in a dye laser, the solvent must be transparent both to the pump radiation and

to the laser wavelength.

 

15

an!

CONDUCTION BAND

 

RECOMBINATION
Ea momma /\/\/\x PHOTON EMISSION
hv=Ea

//

Figure 6. Schematic illustration of fundamental lasing mechanism in a semiconductor
laser [29, 40].

 

 

2.1.3-b. Semiconductor lasers

Diode lasers, based on the various semiconductor materials have proved to be
unique tools in various applications. The fundamental physics of the semiconductor is
illustrated in Figure 6 [29, 32, 40]. Excitation of the semiconductor material, which can
be provided either optically or electrically, can transfer electrons from the valence band
to the conduction band. When the electrons are moved to the conduction band, the
vacant sites in the valence band are referred to as positively charged holes. Electrons can
decay from the conduction band to the valence band by "recombining" with the holes,
since these positively charged holes are attracted to the negatively charged electrons in
the conduction band. When the recombination occurs, the electrons can radiate the their

excessive energy by [29]:

16

Ec _ Ev = E0 = hv Equation 3

where EC is energy state in the conduction band, Ev is energy state in the valance band
and E6 is the band gap energy. The recombination radiation is equivalent to spontaneous
emission, and following stimulated emission in other types of lasers. Semiconductor
lasers have a diode conﬁguration, which contains both the p-type (electron acceptor), and
n-type (electron donor) materials. By applying an electrical potential in forward bias
mode across a diode junction, electrons crossing the semiconductor boundary drop down
from the conduction band to the valence band, emitting radiation by an electron-hole
recombination process.

Some of the major semiconductor lasers and their wavelengths are listed in Table
1 [29]. The distinctive advantages of diode lasers are their small size, easy operation,

economical conﬁguration, high electricity-to-light conversion efﬁciency, and long

lifetime (about 105 hours) [31].

2.1.3—c. Solid-state lasers

Solid-state lasers refer to all optically pumped lasers, which have the solid gain
medium. The active lasing medium in solid-state lasers is generally a transparent crystal
or glass, which is doped with less than 1% of transition metals. Most common dopants
are chromium in the ruby laser, and neodymium in the Nd:YAG or Ndelass laser [32].

The ﬁrst-invented ruby laser has the three-level pumping scheme as shown in

Figure 7 [29]. A ﬂash-lamp is the pumping source for the ruby laser.

17

Table 1. Major semiconductor lasers and their wavelengths [29].

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Compound Wavelengths (nm) Notes
ZnSe 525 First demonstrated in 1991
DeveIOpmental; lifetimes have been short at
AlGaInP 630-680
shorter wavelengths
Active layer between AlGaInP layers; long room
temperature lifetime
x = 0 to 0.45; lifetimes very short for
GaMAles 620-895
wavelengths below 720 nm
GaAs 904
Ino2Gao2As 980 Strained layer on GaAs substrate
In1.,,Ga,,AsyP1.y 1110-1650 InP substrate
InqnGaomAsongQu 1310 Major ﬁber-communication wavelength
Innga42As09Po,r 1550 Major ﬁber-communication wavelength
In GaAs S b ”00-4400 Possible range; developmental; on GaSb
substrate
PbEuSeTe 3300-5800 Cryogenic
PbSSe 4200-8000 Cryogenic
PbSnTe 6300-29,000 Cryogenic
PbSnSe 800029.000 Cryogenic
PUMPING emos
‘Fr m \
FAST
noumormve "'
DECAY
s‘ \‘E!
EIIIIE , IE
BLUE GREEN use};
694.3 nm
4A, enouno LEVEL

Figure 7. Schematic diagram for energy level of the three-level ruby laser [29].

 

18

Pumping is achieved by absorption of the pump light on transitions from the ground level
to the 4F, excited level in the blue spectral region, and to the 4F2 excited level in the
green. Since both of these transitions have a broad absorption spectrum, a broad-
spectrum pumping lamp can be used with reasonable efﬁciency. The population pumped
to these excited states nonradiatively decays to the 2E state, where a population inversion
builds up with respect to the ground state 4A2. Lasing by stimulated emission occurs
between the intermediate state 2E and the ground state 4A2. The stimulated emission has
a wavelength of 693.4 nm. The optical resonator of ruby is often equipped with a Q-
switch, which controls the output by concentrating all of the energy into a single, intense
pulse with duration of about 25 us. A single pulse can have powerful 10 J or more of
energy. The pulse repletion is restricted by heating of ruby rod, hence, the optical
resonator generally has cooling system. The typical emission bandwidth of the ruby laser
is about 0.5 nm. The beam diameter of a low-power ruby laser can be as little as 1 mm,
with the beam divergence of about 0.25 milliradian [33].

Neodymium lasers have two major types: neodymium-doped yttrium aluminum
garnet (Nd:YAG), and neodymium-doped glass (Ndelass) lasers. Even though the
emission characteristics are slightly different due to the inﬂuence of the host lattice on the
neodymium energy level, transitions in the neodymium ions are responsible for laser
action in both the Nd:YAG and Ndelass lasers [29]. The energy-level diagram for
Nd:YAG is shown in Figure 8. Excitation occurs by optical pumping from the 419/2
ground state to a band of excited states. Rapid and nonradiative decay occurs to 4F3/2

upper laser level, where a population inversion builds up with respect to the 4121/2 lower

laser level.

19

 

 

 

 

 

 

 

 

 

 

PUMPING euros
122:! ~.
1:22! NONFI‘D'AWE
\pecav
A ‘\
If ‘ Ir.
Nd:YAG LASER
1.06 pm
PuuP l
"1112
NONRADIATIVE
DECAY
4!” ‘ cnouuo LEVEL

Figure 8. Schematic diagram for energy level of the four-level Nd:YAG laser [29].

The stimulated emission of a wavelength of 1.06 pm occurs between the upper and lower
laser levels. After the stimulated emission, another nonradiative decay follows very
rapidly between the 4111/2 lower laser level to the 419/2 ground state. For Nd:YAG laser,
the output energy at 1.064 um ranges from a tenth of watt to hundreds of watts.
Particularly useful shorter-wavelengths of 532, 355, and 266 nm can also be obtained by
harmonic generation [33]. By Q-switching or mode locking, pulsed output can be
obtained from continuously pumped Nd:YAG lasers. The divergence of Nd:YAG laser
beams can be from a fraction of around 1 to 10 milliradian, and beam diameter is 1-10
mm. The Ndelass laser produces laser radiation at 1.05 pm. The glass lasing medium
in the Ndelass laser has several advantages over the YAG. Since the glass is isotropic
material with cheap and easy fabrication, it can be doped with a large concentration of

neodymium to produce higher power than YAG. However, the glass has a lower thermal

20

conductivity, which prohibits continuous-wave operation. The low thermal conductivity

also limits the pulse repetition rate in pulsed operation [29, 31, 33].

2.1 .3-d. C02 lasers

The carbon dioxide laser is one of the most powerful lasers. The energy levels
involved in carbon dioxide laser action are rotational and vibrational levels, and emission
therefore occurs at much longer wavelengths in the infrared region [34].
The C02 molecule is a linear triatomic molecule with three normal modes of vibration,
which are the symmetric stretch mode, the bending mode, and the asymmetric stretch
mode, as shown in Figure 9a. Thus, the CO2 molecule has three separate quantum
numbers v2, v2, and v3, which have values of non-negative integers. The total energy

associated with a given energy level of this molecule would be described by an

expression with three quantum numbers [34]:

Em, = (v,,v2,v3) = hv,[vl +%)+hvz(v2 +-;—)+ ht/{V3 +15) Equation 4

This equation represents the energy state above the ground state of the molecule. At the
ground state in Figure 9b, the molecular energy is equal to E(0,0,0) = V2(hv1 + hv2 + hv3),
which is the lowest energy of the molecule. As shown in Figure 9b, the most well-known
transition of the CO2 laser involves the radiative transition from E(0,0,1) to E(l,0,0),
which generates infrared laser at 10.6 um. The transition from E(0,0,1) to E(0,2,0) also

generate radiative emission at 9.4 mm [34].

21

(a) o C o

SYMMETRIC ‘——.-—--> . -___.___.

SENDING

*—-——.——.
‘_.._.___..

._——.———-

(b) Wide Bending Asymmetric
stretch

it

   

s
I
III

Enemy (6V)
g
l

 

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
l

 

(0,0,0)

Figure 9. Lasing mechanism of CO2 laser, a) vibrational modes of CO2 molecule, and b)
laser transitions among vibrational levels of CO2 laser [29].

22

The carbon dioxide gas is usually accompanied by nitrogen and helium. Most carbon
dioxide lasers are discharge-pumped, and occasionally RF excitation is used. The
discharge is pulsed at a rate of about 20 per second, and produces output of hundreds of
kilowatts. In C02 lasers, nitrogen and helium are used for collision partner, which
transfer energy to CO2 molecules by collisions. Oscillation occurs between two
vibrational levels in carbon dioxide, while the nitrogen and helium greatly improve the
efﬁciency of laser action. The output power of the laser can be increased by use of the
Q-switch technique [31, 36].

Generally, carbon dioxide lasers are categorized into six types by their nature of
constructions, such as longitudinal ﬂow lasers, sealed-off lasers, waveguide lasers,
transverse ﬂow lasers, transversely excited atmospheric pressure (TEA) lasers, and gas-
dynamic lasers [31]. Maximum output depends on the type of carbon dioxide laser.
Waveguide lasers can produce continuous-wave output up to about 50 W, while sealed
carbon dioxide lasers can reach about twice that level. Longitudinal ﬂow lasers can reach
the kilowatt range, while transverse-ﬂow lasers can produce several kilowatts. Average
powers of TEA lasers range up to a few thousands watts. The powerful 10.6 um
emission of carbon dioxide is ideal for variety of materials processing, such as drilling,

cutting, cladding, and welding.

2.1.3—e. Excimer lasers

Excimer is usually deﬁned as a molecule that is bound only in the excited state.

The word “excimer” is originated from “excited dimer,” meaning an excited diatomic

molecule.

23

Table 2. Various types of common excimers and their wavelengths [33].

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

type excimer wavelength (nm)
N2 126
rare gas dimers Kr2 146
Xe2 172
halogen dimers F2 157
, KrO 558
m gas ”Ides XeO 537.6 and 544.2
ArF 193
KrF 248
rare gas halides XeF 351 and 353
KrCl 222
XeCl 308
HgCl 558
metal halides HgBr 503 and 498
HgI 444

 

 

 

The excimer molecules exist only in excited states, because two constituent atoms are
repulsive to each other in the ground state [29]. Excimer molecules disassemble
immediately upon falling into the ground state. Excimer lasers are a group of pulsed
lasers that incorporate electronic transitions of the excited molecules. Such lasers are
most often composed by the combination of a rare-gas atom (such as Ar, Kr, or Xe) and a
halogen atom (Fl, Cl, Br, or I). Table 2 shows common excimers and laser wavelength
generated from them. Most excimer lasers typically emit in the ultraviolet spectral
region, and some others emit the visible spectrum.

The lasing mechanism for excimer laser can, in a simpliﬁed sense, be viewed as a
sequence of collisional energy exchanges [33]. As shown in Figure 10, the lasing
mechanism for excimer laser is explained in the following with an example of KrF,

which is one of the most powerful and the most commonly used excimer lasers.

 

24

KrF E3 excited state (excimer)

He rapid decay l
collision ' f \
F’ Kr’ m1!— E2 metastable state

 

  

 

i b stimulated
pump "9 Y emissron
electron ’ .1... . . . . ..
discharge ‘
F2 Kr .L— E1 ground state

Figure 10. Lasing mechanism of KrF excimer laser.

Since the outer shell of rare-gas (Kr) atom is already saturated, a bound state is not
formed between the rare-gas (Kr) and halogen (F). In ionization process, excited state of

Kr and F atoms are formed by electrical discharge [33]:

Kr+e’ —) Kr+ +2e’

F2+e'—)F'+F Equations

The positively charged Kr+ ion can enter molecular bond with a negatively charged F ion
by Coulomb interaction. However, reaction of the excited state of the excimer, KrF‘,
requires extra kinetic energy. A collision partner helium acts as a buffer gas, and

transfers extra energy by collision [33]:

Kr“ + F‘ + He —) KrF' + He Equation 6

where ‘*’ signiﬁes the excited state. The formation of the KrF. excimer is the result of a

threefold collision among krypton, ﬂuorine, and helium.

25

100% optical resonator of excimer partial
I reﬂector

 

 
     
 
    
   
   
   

reﬂector
high pressure gas mixture
(3.7 bar, Kr + F2+ He)

 

a beam discharge

  

 

  

Thyratron
switched HV

vacuum

 

 

 

Figure 11. Construction of a typical excimer laser showing optical resonator of electron
beam discharged KrF excimer laser.

After rapid decay to intermediate energy state, the transition of excimer to the ground
state induces the stimulated emission, which generates radiative emission at 248 nm by
[33]:

KrF‘—>Kr+F+hV Equation7
An excimer laser can be technically realized with the excitation using either an electron
beam or by means of a gas discharge. Figure 11 shows construction of a typical excimer
laser, which illustrates structure of the optical resonator of electron beam discharged KrF
excimer laser [29, 33]. Due to the corrosive nature of the halogen species, the entire
structure is made of stainless steel with poly vinyl and Teﬂon components. The cathode
emits electron-beam radiation to produce ionization of lasing medium. The discharge
current is provided by discharging a high-voltage capacitor, using a thyratron switching
device. Generally, the output is obtained by using a totally reﬂecting mirror at the rear of

the laser, and partially reﬂecting quartz mirror at the output front.

26

The most common excimer lasers are XeF at 351 nm, XeCl at 308 nm, KrF at 248
nm, and ArF at 193 nm [37]. The typical pulse energy ranges from 0.5 J to 2 J, and
average pulse duration ranges from 5 ns to 50 ns. Output power is determined by pulse
repetition rate, which generally ranges from a few pulses per second to 200 pulses per
second. Excimer lasers are used primarily for materials processing, medical applications,
photolithography, and pumping of dye lasers. In the materials processing area, excimer
lasers are advantageous because of their wavelength and energy per pulse. Generally,
materials processing requires the laser irradiance over 106 W/cmz, which can be easily
obtained by an excimer laser [38]. Also, the absorption coefﬁcient for most materials is
much greater for ultraviolet wavelengths than for visible and near-infrared wavelengths.
Hence, excimer laser beams are absorbed over a much shorter depth, when materials are
irradiated with such lasers. This enables the production of sharper edges in ablation pro-
cesses. This is also advantageous for such medical applications as laser surgery and
corneal sculpting, which provides optical correction without the need for eyeglasses. In
the lithography ﬁeld, the excimer laser provides a good ultraviolet illumination source at
248 nm and eventually at 193 nm for producing microchip features [37, 38]. Excimer

lasers are also used for the pumping of dye lasers, since all dyes have an extended

absorption into the ultraviolet.

27

2.2. CVD diamond ﬁlm

Carbon exists in three general types of inorganic solid structures, such as graphite,
diamond and Buckyball, as shown in Figure 12 [2-4, 41]. In graphite, carbon atoms are
structured by three coplanar bonds (sp2 type) in bonding length of 1.42 A. The coplanar
bonds form regular hexagons in monoplanes, which are connected by interplanar bonds
in bonding length of 3.35 to 3.44 A. These long interplanar bonds are very weak bonds,
which are broken by even a small force, resulting in the lubricating properties of graphite.
Most forms of inorganic carbons consist of disordered fragments of the graphite
structure. In diamond, carbon atoms form tetrahedral bonds (sp3 type) in bonding length
of 1.54 A. The (sp3 type) bonding results in an extremely rigid, tight and strong structure.
The third structure of carbon after graphite and diamond is the Buckyball, which is
named for the reminiscence of the discoverer, R. Buckminster Fuller. The Buckyball is
made up of 28 to 540 carbon atoms in hexagonal and pentagonal arrays. The most stable

structure is the well known C60, which is composed of twelve pentagonal and twenty

hexagonal arrays.

2.2.1. Growth of CVD diamond

Chemical vapor deposition (CVD) involves a gas-phase chemical reaction
occurring in a controlled environment, which causes deposition of the reactants onto a
solid substrate [2]. The reactants for the synthesis of CVD diamond are typically a small

amount of methane (CI-I4) in hydrogen (H2) at pressures between 102 Pa (~ 1 torr) and 105

Pa (~ 1 atm).

28

 

(cl 06° Buckvball

Figure 12. Three general types of inorganic carbon structures; a) graphite, b) diamond,
and c) Buckyball.

Variations of the CVD processes for diamond include carbon monoxide, oxygen,
hydrocarbons and nitrogen. The CVD process for the diamond is schematically shown in
Figure l3[2]. The gaseous reactants, typically less than 5% of methane in hydrogen
matrix, ﬂow into the reactor. The CVD process for producing diamond ﬁlms requires the
activation of the gaseous reactants. The general methods for the activation are to use a

combustion ﬂame, a hot ﬁlament, and a plasma induced by DC, RF, or microwave.

29

reactant
H2 + 21:14 (< 5%)

{ chamber pressure
1 ~ 40010rr

activation
(plasma. hot filament.)
H2——> 2H

flow and reaction

    

substrate (500 ~— 1200 C)

 

 

Figure 13. Schematic diagram for the chemical vapor deposition of diamond [2].

The gaseous reaction is initiated by dissociation of the molecular hydrogen into atomic
hydrogen. The activation can be achieved by thermal dissociation on a hot ﬁlament or by
electron impact dissociation in plasma [42-44]. The subsequent chemistry is driven by a
series of reactions, in which the activated atomic hydrogen reacts with hydrocarbon
species. These activation and subsequent chemistry is generally remote from the
deposition surface. Transport of carbon atoms to the deposition substrate is carried out
by diffusion and convection [1, 2].

Figure 14 shows the schematic illustration for the carbon phase diagram [3].

30

 

    
 

   
  
 
 
   
    
   
 

 

 

 

  

 

 

 

400
shock wave ;
diamond synthesis .-
--—-—- LIQUID
300-
a DIAMOND
.o
as
an
5 200-
% HTHP diamond
a synthesrs -,.
catalytic H THP
100. diamond synthesis
GRAPHITE
0- ‘ CVD diamond synthesis
o 1000 2o'oo 3600 4600 5000

temperature (°C)

Figure 14. Schematic illustration for the carbon phase diagram, and fabrication regions
for synthetic diamonds. The CVD diamond exists metastably in the graphite
region [3].

The stable phase in the diagram is graphite at lower pressures, diamond at high pressure,
and liquid at extremely high temperatures. The various methods for the fabrication of
synthetic diamonds are indicated in the carbon phase diagram. The process by dynamic
explosive shock wave is shown in the top area of the diamond region, and the processes
by the high-temperature and high-pressure is shown in the lower area of the diamond
region. At the bottom of the diagram in the graphite region, the diamond is synthesized
metastably by CVD at pressure less than the ambient atmosphere and at temperature near

1000 °C. Since the CVD diamond exists in metastable state, it is converted to graphite

when it is heated to about 1000 °C or greater [3].

31

In the CVD process, the resulting ﬁlms are polycrystalline, with a morphology
that is sensitive to the precise growth conditions. Texture and morphology of CVD

diamond ﬁlms primarily depends on methane concentration and substrate temperature.
These processing conditions determine the growth parameter, a = (Koo/th/S , where

V100 and Vm describe the ratio of the growth rates on {100} and {111} planes,
respectively [45]. In epitaxially textured diamond ﬁlms, which are grown on {100}
single crystal silicon wafer, the growth parameter results in various distinctive textures
and surface morphologies.

Growth of CVD diamonds is a chemical process, which takes place by
incorporation of carbon atoms into the crystal lattice [2]. The carbon atoms in the
diamond lattice are linked by strong sp3 covalent bonds. Crystal planes of diamond ﬁlms,
such as {100), {110} and {111} exhibit different planar densities and surface energies.
Dangling bonds on the surface of CVD diamonds are terminated by hydrogen atoms.
According to these crystallographic properties, Figure 15 shows geometry of hydrogen
terminated (100), (110), and (111) plane of a diamond lattice. For the (100) plane in
Figure 150, ideal hydrogen truncation, which locates the adjacent hydrogen atoms closer
than molecular hydrogen, give rise to violation of steric constants. An example of
generalized reconstruction is shown in Figure 15d, which compensates steric constants
and lattice distortion [2, 46].

Growth rates for the CVD processes vary considerably, and generally, the higher

growth rates can be achieved by the expense of a corresponding loss of ﬁlm quality [1].

32

    

    
   

 
 
 

   

1%
l
.1

'l‘
§ \§ -
I ll ii' ii I|i
91%Ig‘llgu
I I
IDIIQIH§I

 
    

Figure 15. Geometry of hydrogen terminated (100), (110), and (111) plane of a diamond
lattice, a) (111) plane, b) (110) plane, c) (100) plane, d) reconstructed (100)
plane. Large and dark circles represents carbon atoms, and small and light
circles represents hydrogen atoms [2].

The quality of the CVD diamond ﬁlms is related to some factors, such as the ratio of sp3
to sp2 bonding, hydrogen (C-H bond) contents, and the crystallinity [43, 47-50]. In
general, CVD processes with combustion activation deposit diamond at high rates,
typically 100 to 1000 urn/hr. However, the process is limited to a localized area, and the
quality of the deposited diamond is poor due to the poor controllability of the combustion
process. In contrast, the hot ﬁlament and plasma methods produce high quality diamond
ﬁlms, however these activation methods have much slower growth rates, typically 0.1 to

10 pm/hr [51].

Table 3. Comparison of material properties between CVD diamond and other materials

33

 

 

 

 

 

 

 

[3—5, 41].
CVD other materials ratio
diamond (diamond IO OIIICI' materials)
elastic modulus 393 (A1203) 2.6
(Gpa) 1 035 186 (Ti) 55
Knoop hardness 2190 (WC) 3.2
(kg/m2) 7000 800 (Hardened steel) 8.7
thermal conductivity 3.80 (copper) 5.3
(Watts/cm-°C) 20 1.5 (graphite) 13.3
friction coefficient 0.10 (lubricated metals) 0.5
(friction force/normal thrust) 0-05 0-10 (graphite) 0-5
bandgap 1.10 (silicon) 5.0
(ev) 5.45 1.43 (GaAs) 3.8
resistivity 103 (silicon) 1013
(52cm) 1016 10°(GaAs) to7

 

 

 

 

 

2.2.2. Properties of CVD diamond

 

CVD diamond ﬁlm inherits superior material properties of a natural diamond.
The strong sp3 covalent bonding among carbon atoms gives rise to unmatched material
properties of diamond. Various material properties are compared between diamond and
other materials in Table 3. The ratios in the last column of Table 3 indicate the diamond
to other materials ratio in the given material property. One of the great properties of
diamond is its chemical inertness. CVD diamond resists almost all forms of chemical
attack at room temperatures. CVD diamond can be safely cleaned in strong reagents such
as boiling sulfuric acid and hydroﬂuoric acid. However, due to the metastable existence
of diamond, it has been oxidized at high temperatures in caustic alkalis and monatomic
gases such as oxygen and hydrogen [52].

The extremely high elastic constants of diamond make the values of moduli,

strength, and hardness the highest of any other materials. Like other ceramic materials,

pure diamond is brittle and exhibits low fracture toughness. 0n the contrary, the fracture

34

toughness for polycrystalline diamond is considerably higher. This is mainly due to the
presence of a second phase from the CVD process. In addition to its high strength and
hardness, diamond also exhibits the lowest friction coefﬁcient of any solid material, as
well as the ability to propagate sound at high velocities [3, 4, 41, 52, 53].

Diamond possesses many unmatched electron properties as well. It has the
highest electrical resistivity of materials. Theoretically, ideal diamond should exhibit

resistivity near 1070 Q-cm. However, impurities reduce this value considerably so that

resistivity value near 1016 Q-cm is observed for CVD diamond. As a semiconductor,
diamond exhibits the highest saturated electron velocity, the lowest dielectric constant,
the highest dielectric strength, and the largest band gap of any semiconducting material.
The common acceptor (p-type) impurity in CVD diamond is boron [52].

One of many remarkable properties of diamond is its thermal conductivity. In
contrast to metals, where conduction electrons are responsible for the high thermal
conductivity, heat is conducted in electrical insulators by lattice vibrations. This thermal
conductivity of diamond comes from phonon heat transfer, which proceeds readily across
diamond’s tetrahedral crystal lattice of low-atomic-mass atoms and stiff covalent bonds
[41]. The thermal conductivity of diamond is about ﬁve times larger than that of copper.
Diamond also exhibits the lowest speciﬁc heat and highest Debye temperature of all solid
substances.

Diamond has the widest spectral transmission range (225 nm to 25 jun) of all
known solids. It exhibits high transparency throughout the visible, near infrared, and
thermal infrared wavelengths. Theoretically, ideal diamond is absolutely transparent to

visible light, but impurities and defects in CVD diamond cause absorption in visible

35

region. Diamond also shows luminescence, which can be excited by electricity, phonon
irradiation or particle bombardments. The luminescence takes the form of ﬂuorescence,

phosphorescence, or therrno-luminescence [3-5, 41].

2.2.3 Applications for CVD diamond

The superior material properties of CVD diamond have exhibited a great potential
in various applications. Recent successful developments of vapor-phase-growth
technology have made large-area deposition available at low production cost, and these
have expedited the industrial applications of CVD diamond. The commercialization of
diamond is limited at current state, leaving great opportunities for future applications.
Currently, the major applications for CVD diamond are in the limited areas of coated
tools, speaker diaphragms, and heatsinks. However, substantial progresses in research
have been accomplished for near-future applications in sensors, optical windows,

semiconductor devices, ﬁeld emitters and MEMS [53].

2.2.3-a. Coated tools

CVD diamond has been applied as a coating on cutting tool inserts. CVD
diamond-coated drill bits, reamers, and countersinks are now commercially available for
machining non-ferrous metals, plastics, and composite materials. The CVD diamond-
coated tools have exhibited a longer life, a shorter machining time, and a better ﬁnish, as
compared to conventional tungsten carbide tool bits. However, the application for coated
tools is limited to the non-ferrous machining. In any application of coated tools, the
diamond will be heated up due to the involved friction. Carbon has strong interstitial

afﬁnity to ferrous materials. In case of machining of iron or steel, the diamond coating

36

reacts with the workpiece, and dissolves into it. Research efforts are currently underway
to place suitable barrier-layer materials to allow machining on iron and steel with
diamond-coated inserts. Diamond coatings for large-area wear resistance are also
currently in progress. These coatings will greatly increase, with reduced lubrication,

lifetimes of large components, such as gearboxes, engines, and transmissions [3, 4, 41,

52, 53].

2.2.3-b. Heatsink

Diamond, as an electrical insulator, has a thermal conductivity about ﬁve times
superior to that of pure copper. Diamond has been investigated for heatsinks. and
applied to heat sinks for laser diodes, and for small microwave integrated circuits. For
integrated circuits, devices mounted on diamond can be packed more tightly without
overheating. Reliability can also be expected to improve from lower junction
temperatures. Diamond also retains excellent insulating and dielectric characteristics.
These superior properties make CVD diamond an excellent candidate as a packaging
material for high power and high frequency components. However, diamond has a
smaller coefﬁcient of thermal expansion (Cl‘E) than that of other semiconductor
materials. Mismatching of CTE, between diamond and semiconductor device, can cause
cracks at the interface. Thus, the die size on a diamond heatsink is limited to several
hundred microns. For larger heatsink, various research efforts are currently undergoing

to reduce the drawbacks from the CIE mismatch [3, 4, 41 , 52, 53].

2.2.3-c. Optical windows

37

Diamond has the highest transparency in wide range from infrared to x-ray. Due
to these excellent optical properties, diamond can be coated to optical components.
Diamond has been successfully adopted as a protective coatings for infrared (IR) optics
in harsh environments. Most IR windows are currently made from materials such as ZnS,
ZnSe, and Ge. These materials have excellent IR transmission characteristics, but are
brittle and easily damaged. A thin protective barrier of CVD diamond coating provides
the answer for the IR optics. The IR windows can also be made from freestanding
diamond ﬁlms, which can be grown to a thickness of a few millimeters. Since rough
surface of polycrystalline CVD diamond can cause attenuation and scattering of the
transmitted IR signal, technical developments for polishing diamond surface have to be

accompanied with the application to the optical windows [3, 4, 41, 52, 53].

2.2.3-d. Semicondpctor devices

Diamond retains semiconducting properties with a large energy band gap of 5.45
eV and a relatively small lattice constant, compared to other semiconductors. Even
though these properties make diamond ﬁlms difﬁcult to form a semiconductor with
hetero-junctions, the large band gap is a unique characteristic of diamond for high
temperature and high power operation, associated with its high thermal conductivity. The
doping of diamond changes it from an insulator to a semiconductor, and opens up new
range of potential electronic applications. However, major problems have to be solved to
achieve practical application of diamond-based electronic circuits.

One of the major problems is the difﬁculty to produce n-type doped diamond
ﬁlm. The p-type doping is currently possible by incorporation of boron atoms into the

diamond lattice. This incorporation of boron atoms is achieved by addition of a few

38

percent of B2H6 to the gas mixture for CVD process. However, the doping, with atoms
larger than carbon, is very difﬁcult due to the close packing and rigidity of the diamond
lattice. The n-type doping typically involves dopants like phosphorus or arsenic atoms,
which are larger than carbon atoms. Alternative dopants such as lithium are currently
investigated for the n-type doping on CVD diamond. Another problem is that CVD
diamond is grown with polycrystalline assemblies, which contain grain boundaries,
twins, stacking faults, and other defects. All of these reduce the lifetime and mobility of
carriers [53].

One further difﬁculty is to achieve patterning on diamond ﬁlm. The patterning is
essential to engrave circuits in required micron or even submicron geometries. Dry
etching, using oxygen-based plasmas, can be used, but it involves very slow etching rates
with complex procedures. Alternative patterning method is the selective nucleation by
lithography-pattemed diamond growth. In the process, a lithography-pattemed
photoresist layer, in which diamond seeds are embedded, is placed in CVD reactor for the
diamond growth. Besides its step-intensive procedure, the process exhibits lateral growth
of diamond ﬁlm, which limits the resolution and aspect ratio of the patterned structure
[54-57].

Despite these difﬁculties, remarkable research efforts have been exerted on CVD
diamond-based semiconductor devices. Piezoelectric effect devices, radiation detectors,
and the ﬁrst ﬁeld-effect transistors have been reported recently from laboratories, as a
prelude to the commercial diamond devices. Especially, application of diamond, as an

electron emitter in ﬂat panel displays, draws a great deal of attention at the current

moment [52, 53].

39

2.2.3-e. Sensors and MEMS

Various sensor applications for CVD diamond are currently under investigations,
including a pressure sensor using piezoresistivity, a thermistor using electrical
conductivity, a photodetector using photoconductivity, and a cantilever sensor for atomic
force microscopy. Currently, most of the MEMS devices have been based on silicon.
This is due to the technology, which has been accumulated in manufacturing of silicon-
based semiconductor. Since these silicon-based systems have exhibited rapid wear from
high friction of the system, only very few MEMS devices involve actual mechanical
operation. The excellent material properties in friction, wear, and thermal conductivity
make CVD diamond uniquely qualiﬁed for MEMS applications. To utilize the excellent
properties of the diamond ﬁlms in sensor and MEMS applications, micromachining and
patterning of diamond ﬁlms are primarily required. For CVD diamond, conventional
machining and lithography-based patterning are difﬁcult due to the high wear resistance
and the chemical inertness. Recently, such as in this research, the pulsed laser ablation
has been demonstrated as a new method for making patterned structures and micro-

components on CVD diamond [52, 53].

Chapter HI

EXPERIMENTAL

3.1. CVD Diamond Films

Diamond syntheses by CVD, as reviewed in Chapter 2, have been developed by
various thermal activation methods of gaseous reactants [3-6, 43, 45, 58]. The reactant
gas mixture includes mainly a small amount of CH4 (< 5%) in H2 gas matrix, with some
other supplementary gaseous species. The activation of the reactants is achieved by
various energy sources, such as hot ﬁlaments, plasmas, and combustion ﬂames [6].
Among the vapor phase processes, microwave plasma assisted CVD method has been
extensively practiced by virtue of its distinctive advantages. These advantages include
reduced contamination, higher concentration of activated reactants, and centralized
deposition process [43]. To grow high quality, and large area diamond ﬁlms, a 7-inch
microwave cavity plasma reactor (MCPR7) has been developed in the Micro and Nano
Engineering Center at Michigan State University [43]. All polycrystalline diamond ﬁlms
in our research study have been processed in the third generation MCPR7. Figure 16
shows the schematic diagram for the MCPR7. The mass ﬂow controllers regulate and
mix the reactant gases (H2, CH4 and CO) before they are introduced in the reaction
chamber. The microwave power supply (Carber, model S6F/4053) is the variable

microwave power source with maximum output of 6 kW at 2.45 GHz.

40

41

RECTANGULAR WAVE
MASS FLOW l
CON TROLLERS

/ 7 INCH QUARTZ DOME

 

 

 

 

 

 

 

:jﬂ

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PLASMA MICROWA
—-7";—'— POWER SUPPLY
PROCESS CHAMBER
THROTTLE VALVE
:l MECHANICAL
_ ROUGHING
PUMP
COMPUTER
CONTROLLER
EXHAUST
N2

 

 

 

Figure 16. Schematic diagram for the 7-inch microwave cavity plasma reactor (MCPR7)
at Michigan State University [43].

The mechanical roughing pump is used to pump down the chamber pressure up to ~ 0.01

torr. The ﬂow of nitrogen gas near the exhaust dilutes the exhaust gas mixture, which is

hot and ﬂammable. The entire vapor deposition process can be monitored and controlled

by a computer controller. All diamond ﬁlms used in our research study were hetero-

epitaxially grown on 2-inch or 3-inch diameter single crystal silicon wafer, as shown in

Figure 17.

42

 

ON 3 INCH-D , ,
SILICON WAFER

 

 

 

Figure 17. Hetero-epitaxially grown diamond ﬁlms on 2-inch-diameter and 3-inch-
diameter single crystal silicon wafers.

Texture and morphology of CVD diamond ﬁlms primarily depend on methane
concentration, and substrate temperature. In hetero-epitaxially textured diamond ﬁlms,
which are grown on {100} single crystal silicon wafer, the growth parameter results in
various distinctive textures and surface morphologies. In this investigation, diamond
ﬁlms with {100), {111} and mixed surface morphologies are chosen to be subjected to
the excimer laser ablation. The grain size and vertical thickness of the subjected diamond
ﬁlms ranged from 2 pm to 50 um, and form 4 pm to 270 pm, respectively. The
processing parameters for the all CVD diamond ﬁlms used in this study is listed Table 4,
where P is the chamber pressure, T, is the silicon substrate temperature, CH4/H2 is the
methane concentration, time is the reaction time, G, is the average grain size, V, is the

average vertical thickness and ref. is the reference for the processing parameters.

43

Table 4. Processing parameters for the CVD diamond ﬁlms used in this study.

 

 

 

 

 

 

notation P (lorr) T. (°C) CH/HZ (%) time (h) 6. (um) V, (um) ref.
AT109 80 845 2 8 2 7 [44]
BW062 38 850 2 8 2 4 [59]
BW097 38 860 1 8 2 6 [59]
ST204 1 20 1060 3 75 40 270 [44]
ST235 i35 1057 3 20 50 1 10 [44]

 

 

 

 

 

 

 

 

 

 

DIAMOND FILM

SUBSTRATE SIDE
SURFACE

 

300 um

 

Figure 18. Cross section of free standing diamond ﬁlm (ST204) showing the rough ﬁlm
surface of diamond-growth side (upper surface), and the ﬂat surface of the
substrate side (lower surface).

Among the diamond ﬁlms in Table 4, ST204 and ST235 are the freestanding diamond
ﬁlms. To acquire a freestanding diamond ﬁlm, the silicon wafer substrate, where the
CVD diamond ﬁlm was grown by the hetero-epitaxial growth, was completely dissolved
in the etching solution (50%HNO3 + 25%HF + 25%CH3C00H). The substrate side of
the freestanding diamond ﬁlm retains ﬂatness similar to that of the polished silicon wafer.

The cross section of the freestanding diamond ﬁlms (ST204) is shown in Figure 18.

3.2. MP-I Maskless Patterning System

The innovative maskless patterning technique employs pulsed irradiation of a
focused laser beam on a target material, which is translated to the programmed positions
by a micro computer numerical controlled (micro-CNC) stage. To produce micro
patterns, and structures using laser ablation technique, the maskless patterning system
MP-I has been constructed in the High Energy Laser Processing Laboratory (HELP) at
Michigan State University. Figure 19 shows the overview and the schematic of the MP-I
system, which is mainly composed of an excimer laser, imaging optics and the micro-

CNC stage. The components of the MP-I system are discussed in next sections.

3.2.1. Excimer laser

A KrF excimer laser, COMPex 301 manufactured by the Lambda Physik®, was
used for the MP-I maskless patterning system. The excimer laser has the wavelength of
248 nm from the lasing medium of krypton ﬂuoride. It has a rectangular pulsed beam in
TEMoo mode. The maximum pulse energy from its resonator is 1.5 Joules, and the
maximum repetition rate is 10 times per second (10 Hz). The premixed gas, which is
composed of 2.7% krypton, 0.1% ﬂuorine, 16.2% helium, and 81% neon, were used for
the lasing gas for the excimer laser. The speciﬁcations of the laser are listed in Table 5.

The excimer laser beam from its resonator has an energy distribution proﬁle. The
rectangular beam (13x30 m2) has the Gaussian proﬁle in its vertical section and ﬂat-top
proﬁle in its horizontal section [60]. The proﬁle of the beam is shown in Figure 20. In
the MP-I system, the apertures were placed to select the central region of the raw excimer
laser beam. The uneven ablation from the beam proﬁle was minimized by using the

central region of the beam.

45

 

(b) BEAM

  
 
 
 
  

BEAM . - .5. ,
REFLECTOR ‘ ,1. EXCIMER LASER
‘ .- ' Ho-No
AUTOAT c GUloING LASER
APERTURE

 

  

OBJECTIVE LENS It ,
' ROCESSING GAS
DEUVERY UN

 
 
 

 
   

PLANAR
CONVEX LENS

 
    
    

REGULATED

71 ,I/L? GAS STREAM

 
 

MOTION STAGE cENTRAL OOMPUTER

°°NT m E" - MOTION STAGE PROGRAMMER
- INDEX MODULE - EXOIMER LASER CONTROLLER
- POWER SUPPLv . PRocEss OBSERVATION
- SYSTEM DISPLAY

«u.

   

5MOTION AXES , :I:
MICRO—ONO $9 *
STAGE r

I

ST CK
CCONTROLLER

  

MP-I Maskless Patterning System

MOTION AXES
SYNCHRONIZER

Figure 19. a) Overview of the MP-I maskless patterning system, designed for this
research, and b) the schematic diagram of the MP-I system.

46

Table 5. Speciﬁcations of the KrF excimer laser, Lambda Physik® COMPex 301.

average

3x1 mrad (WxH)
13x30

 

(WxH)

           
  
   

  

- ”0’1"."

’ii

 

, .vg- 1.1.:I'IA . ii};;i’;‘g§;~\“‘
’ A II x,
”' "’ Ilium: [In "" 1"") \“

  
   

    

O
.

   
  
     

   
 

\.
\,
I“) \\\\\\‘;-g ..........
m, t\\\\‘,t

.......

1'. nnnnnnn a ---------
Ultra-.llilllpoa-nln
Dotlltnlllﬂlpplllallv

 
 

Figure 20. Beam energy proﬁle of rectangular beam (13x30 mm2) from the KrF excimer
laser showing a Gaussian proﬁle in its vertical section and ﬂat-top proﬁle in
its horizontal section [60].

47

CONVEX LENS

LASER IMAGING SYSTEM

 

Figure 21. Construction Of the laser imaging system according to the thin lens principle.

3.2.2. Imaging optics

To engrave small features on a target, the construction of the laser imaging system
is required according to the thin lens principle. Figure 21 shows the schematic of the
laser imaging system, in which the laser illuminates the demagniﬁed image from the

mask. The thin lens principle is written as [61]:

1+1“: E ti 8
i 0 f qua on

where i is the distance between the lens and the focused imagine, a is the distance
between the mask and the lens, and f is the focal length.

The imaging optics in the MP-I system was constructed for this research
according to the principles of the laser imaging system. The uniqueness of the MP-I
system is that it uses small circular apertures instead of the patterned masks. The concept
of the maskless patterning is the illumination of the focused small laser beam on a
translating target. Various patterns can be rapidly Obtained by programmed translation of
the target material. The maskless patterning addresses the time consuming fabrication of

the masks in the lithography-based patterning, in which each patterning requires the

48

fabrication of a patterned mask.

The imaging optics in the MP-I system includes an automatic aperture unit, a set
of planar convex lenses and the gas delivery unit. The components of the imaging optics
are illustrated in Figure 22. Figure 22a shows the schematic diagram of the imaging
optics. The automatic aperture unit and the beam shutter in Figure 22c are controlled by
the motion stage controller (see Figure 19), and the Operation can be programmed
together with micro-CNC stage. The automatic aperture unit has four apertures of
different sizes in a rotating disk. The DC motor, which is controlled by the motion stage
controller, rotates the disk to automatically change the size of the aperture. A rectangular
pulsed laser beam passes through the circular aperture, and then the circular beam is
focused by the two planar convex lenses, as shown in the laser beam path in Figure 22b.
Various spot sizes can be available by changing the size of apertures in the automatic
aperture unit. The size of the apertures in the automatic aperture unit, and resultant
focused spot sizes, at the target, are list in Table 6. The beam shutter is essential for the
continuous patterning process of discrete patterns. Since the KrF excimer laser cannot be
turned on and off very quickly (the excimer laser requires ~ 5 minutes of stabilization
after turned on), the blocking of the laser source is required for the pattering of successive
discrete patterns (for example engraving disconnected capital letters such as MSU). The
beam shutter uses stepper motor, whose motion is programmed together with the micro-
CNC stage. An example of the laser ablation for the discrete pattern is in shown Section
6.1.3.

Figure 22d shows the gas delivery unit, which incorporates the gas nozzles and
objective lens. Three gas nozzles are installed around the objective lens, to deliver
dynamic gas streaming over the irradiation spot. The nozzles are positioned about 3 mm

from the irradiation spot and 30° degrees to the ﬁlm surface.

BEAM
REFLECTOR

OBJECTIVE LENS E
PROCESSING GAS
DELIVERY UNIT

(a) MP-1 system

49

AUTOMATIC T,’
APERTURE '

  
   

PLANAR CONVEX
LENS

REGULATED GAS
STREAM

imaging optics

(c) automatic aperture unit
and beam shutter

 

REFLECTOR T‘ LASER BEAM

 

APERTU RE

L

 

PLANAR CONVEX FL: 295 mm

   

GAS
STREAM

   
 

PLANAR CONVEX FL: 50 mm

 

 

(b) diagram for the laser beam path

 

(d) dynamic gas delivery unit

Figure 22. Illustration for the components in the imaging optics in the MP-I system; a)

schematic diagram for the imaging optics, b) beam path diagram for the
imaging optics, c) automatic aperture unit and beam shutter, and d) gas
delivery unit for the dynamic gas streaming. (these units were all designed and

built for this research.)

50

Table 6. Size of the apertures in the automatic aperture unit and resultant beam spot size

 

 

 

 

 

at the target.
aperture size (mm) spot size (pm) at the target
9.5 750
6.3 500
2.2 175
1 80

 

 

 

 

  

DIRECTIONOFTHEDYNAWGASBTREAHNG
(OFFSETBYS'TOTHECENTER)

 

 

Figure 23. Schematic diagram showing offset of the direction of the dynamic gas-
streaming nozzle.

The diameter of the gas nozzles is 2 mm and the maximum gas ﬂow rate of the
unit is 12x104 m3/sec. The nozzles are pointing the irradiation spot, with ~ 3° offset to
the center, streaming around the center of the spot. The schematic diagram in Figure 23
shows the offset of the gas nozzles for the dynamic gas streaming. The offset was set to

prevent the static pressure, and to create the dynamic vortex streaming around the center

of the irradiation spot.

51

3.2.3. Micro computer numerical control (micro-CNC) stage

In the maskless patterning system, programmed translations of target materials are
required to produce micro patterns, and structures, using laser ablation technique. The
micro-CNC stage has been constructed in the MP-I maskless patterning system for the
programmed target translations. Figure 24 shows the schematic diagram for the motion
stage in the MP-I system and the speciﬁc features of the motion stage. The micro-CNC
stage contains a 5-motion—axes stage (x—y-z, rotation and tilt), which allows a target
translation in three-dimensional directions. As shown in Figure 24a, the micro-CNC
stage is controlled by the IBM-PC based motion stage controller, which incorporates the
index module, the translator, the stepper motor driver and the DC power source. The
index module is from the Microkinetics Co. (Kennesaw, GA), model QuickPhase, which
can control up to 3 axes simultaneously. The index module is programmed by the
software (Microsoft, QuickBasic) for the patterned translations. The motion axes
synchronizer is a switcher, which can choose the 3 axes for the simultaneous motion
control from the 5-motion-axes in the micro-CNC stage. The central computer in the
system synchronizes the excimer laser and the micro-CNC stage, and also monitors the
process through the in-situ observation camera.

The features of the micro-CNC stage are shown in Figure 24b, in which the X-Y-
Z, rotation and tilt stages are indicated. In the micro-CNC stage, the X and Y motion
stages are made by ArdelKinematic Co., and all other components are designed and

constructed by the High Energy Laser Processing Laboratory.

52

 

 

  

MOTION STAGE CENTRAL COMPUTER

r CONTROLLER
4.. - INDEX MODULE - MOTION STAGE PROGRAMMER
x . - POWER SUPPLY - EXCIMER LASER CONTROLLER

   

- SYSTEM DISPLAY - PROCESS OBSERVATION

SMOTION AXES I ’ ICRO z

JOY STICK
MICRO-CNC . ”5"
STAGE - .4 - CONTROLLER
. MACROZ
“"5 "

 

MOTION AXES
SYNCHRONIZER

(a) schematic diagram for the 5-motion-axes micro-CNC stage in the MP-1 system

 

(b) front View of the 5-motion-axes micro- (c) side view of the 5-motion-axes micro-
CNC stage CNC stage

Figure 24. 5-motion-axes micro-CNC stage in the MP-I system; a) schematic diagram,
b) front view, and c) side view. (The systems, and subsystem shown in these
ﬁgures, were designed and built for this research.)

53

Table 7. Speciﬁcations for the components of the 5-motion-axes micro-CNC stage.

 

 

 

 

 

 

stepper motor motion stage mximum minimum translation
resolution resolution speed speed limit
X stage 7.5 °lstep 4 urn/step 7.2 mm/sec 200 W560 13 mm
Y stage 7.5 °lstep 4 urn/step 7.2 mm/sec 200 tun/sec 13 mm
Z stage 0.9 °lstep 0.025 tun/step 45 uni/sec 1.25 Inn/sec 5 mm
rotation stage 0.9 °lstep 0.22 °lstep 396 °lsec ll °lsec 360 °
tilt stage 0.9 °lstep 0.018 °lstep 32.4 °/sec 0.9 °/sec 360 °

 

 

 

 

 

 

 

 

The side view, in Figure 24c, shows the macro-Z motion stage, which is designed to
translate the entire micro-CNC stage in the longitudinal direction. The macro-Z motion
stage is required for the specimens at various heights, and is driven by a DC motor with a

large translation limit of 18 cm.

The speciﬁcations for the motion axes of the micro-CNC stage are listed in Table
7. All stepper motors in the micro-CNC stage have the bipolar conﬁguration, and are
capable of operating in half-stepping mode [62]. The spatial resolution for the two
dimensional patterning, for which the X and Y motion stages are used, is 4 um for the
MP-I system. The minimum speed is the lowest speed for the continuous movement of
the stages. The minimum continuous speeds are important to engrave continuum linear
features using the pulsed irradiation from the excimer laser. The size of the two-
dimensional patterning is limited to 13 x 13 mm2 because of the translation limits of the
X and Y motion stages. The rotation and tilt stages are designed to have 360° turns. The
speciﬁcation of the micro-CNC stage is one of the most important criteria that have to be

considered for designing patterns on the CVD diamond ﬁlms.

Chapter IV

LASER-DIAMOND COUPLING

4.1. Laser-Diamond Interaction

4.1.1. Excimer laser irradiation on CVD diamond film

Typical UV-lasers make use of stimulated emission from excited molecular gases,
such as ArF, KrF, XeCl, or XeF. Pulsed output of the lasers has a wavelength range from
193 nm to 351 nm, and duration time range from 10 us to 30 ns. Due to the
characteristics of UV-lasers (i.e., short radiation wave length and rapid pulse duration
time), large amount of radiation energy can be transferred in a thin layer of a target
surface. When the laser irradiance, deﬁned by Watt/cmz, exceeds an inherited threshold
value of the target material, a thin layer is instantaneously evaporated by breaking atomic
bonds upon the irradiation [63-67]. Upon the ablation process, most of the absorbed
energies are used up for the sublimation of exposed atoms within tens of nanosecond
range. This causes localized ablation only where the photon energies are absorbed. The
selective ablation makes precision micromachining possible by imaging a desired pattern
on a target. The laser in the setup is the KrF excimer laser (Lambda Physik®, model
COMPex 301) with a wavelength of 248 nm, a rectangular pulsed beam of 1.3x3.0 cm2 in

TEMOO mode, a maximum pulse energy of 1.5 J and a maximum repetition rate of 10 Hz.

54

55

PIN-HOLE MASK (1 mm DIA.)

REFLECTOR

 

 

 

 

 

/ PLANAR CONVEX LENS (1:295)

DUDE LASER
PLANAR CONVEX LENS (1:101)
/

DIAMOND FILM

X-Y-Z TABLE I 1

Figure 25. Schematic diagram of the excimer laser setup for the laser-diamond
interaction.

Excimer laser setup used for the laser—diamond interaction is shown in Figure 25.
Since the imaging system follows the thin lens principles of optics, the imaging plane is
determined by the focal length of the convex lenses and the distance between the mask
and the convex lenses [61]. A target surface is placed at the imaging plane where the
demagniﬁed pin-hole mask (1 mm diameter) is sharply focused for the ablation process.
The imaging system is composed of a X-y-z specimen stage, two planar convex lenses (f
= 295 mm and f = 101 mm, respectively) and a dielectric reﬂector (more than 99.5 %
reﬂectivity). Two guiding lasers are used to aid focusing of the excimer laser imaging
system. The crossover point of the two visible guiding lasers marks the imaging plane of

the system.

56

 

Figure 26. Surface morphology of as-synthesized CVD diamond ﬁlm subjected the laser-
diamond interaction.

Figure 26 show the as-synthesized diamond ﬁlm used in this preliminary laser-
diarnond interaction experiments. The surface morphology of the diamond thin ﬁlm
shows the fully faceted 3-D diamond crystals, with stacking-fault reentrant grooves [4].
The polycrystalline diamond ﬁlm (AT109) was hetero-epitaxially grown on a single
crystal silicon wafer, and has an average grain size and thickness of 2 um and 7 urn,
respectively. The diamond ﬁlm was subjected under three different processing
environments, such as the ambient air, the vacuum condition and the gas-streaming

condition. Figure 27 shows the schematic diagrams for the processing environments.

57

excimer laser pulse

 

diode wiring laser

 

 

(c)

Figure 27. The schematic diagram showing irradiation conditions in; a) the ambient air,
b) the vacuum condition, and c) the gas-streaming condition.

58

The interaction, between the CVD diamond and excimer laser pulses, showed drastic
changes among the different processing environments. The ﬁlm was subjected under the
same irradiation conditions, in which the laser irradiance, repetition rate and number of
pulses were ﬁxed at 4x108 W/cmz, 1 Hz, and 20 times, respectively. A circular beam

spot (145 um diameter) was illuminated on the ﬁlm surface by the pin-hole mask in the

imaging system.

4.1.2. Irradiation in ambient air

Series of SEM micrographs in Figure 28 are taken from the irradiation in the
ambient air, which is under stationary air in ambient atmosphere. In the ambient air, the
ablation-debris deposition is observed that the edges are spoiled by the accumulation of
the ejection. In this process, the pulsed irradiation eradicated the diamond ﬁlm, and
revealed the silicon substrate of the rufﬂed crater. In Figure 28a, the circular spot at the
center was irradiated under previously described imaging system. The diamond surface
around the irradiated spot show distinctive plasma affected zone (PAZ), which has
somewhat symmetrical, ring-shaped patterns with spikes. The areas of PAZ indicated by
l, 2, and 3 in Figure 28a are magniﬁed and observed in Figure 28a—1, 3a—2 and 3a—3,
respectively. In Figure 28a-1, the area near the edge of the spot has suffered from heavy
deposition of debris and damage on diamond crystals. The deposition is gradually
reduced in Figure 28a—2 and 3a-3 as the distance increases from the spot. The debris and
deposition of the ejected materials are observed at distances up to 10 times the spot
diameter (145 pm). The PAZ is caused by combination of deposition of ablation debris
and thermal damage upon the expansion of high temperature plasma. Figure 28a-3 shows

the debris in irregular shapes, which were ejected from the diamond ﬁlm and substrate

59

material. The temperatures of ablation-induced plasma have been measured around 103 ~
104 K from irradiation on graphite targets [68-70]. The temperature distribution, around
the irradiated spot, is assumed to have an exponential decay type of radial distribution,
dispersed due to the formation of the plasma [66]. From Figure 28b, it is obvious that the
material ejection and redeposition occurred around the spot. The irradiated spot appears
to be a crater, which has rufﬂed bottom from the surface melting. In this process, the
pulsed irradiation eradicated the diamond ﬁlm, and revealed the silicon substrate of the
rufﬂed bottom. In Figure 28c, the crater is tilted and observed in SEM. Uneven depths
of the crater were observed. The deep and rufﬂed crater indicates the melting of the
silicon substrates, and the edges of the spot are piled up with injected materials.

A part of the spot edges is magniﬁed in Figure 29. The radial-symmetric liquid
ejection from the silicon substrate damaged the diamond ﬁlm layer around the spot edges
due to high temperature instability of the synthesized diamonds [3-5, 58]. Inside the

piled up edges, the crater has bumpy structure with small wavelets as indicated by an

arrow.

60

300 um

 

Figure 28. SEM micrographs showing excimer laser irradiation in the ambient air; a) the
irradiation spot and surrounding with distinctive PAZ marked by 1, 2, and 3,
b) the irradiation spot, c) highly tilted (75°) image for the irradiation spot, a—l)
magniﬁed view of zone 1 from the ﬁgure a, a-2) magniﬁed view of zone 2
from the ﬁgure a, a-3) magniﬁed view of zone 3 from the ﬁgure a.

61

 

Figure 29. Edge Of the irradiation spot in the ambient air showing the radial-symmetric
ejection and damage near the edges.

The wavelets are formed by the surface convection of the substrate and the propagation
of stress waves upon expansion of high temperature plasma [26, 66]. During the short
dwelling time (25 ns) of the excimer laser pulse on the ﬁlm surface, atomic or molecular
bonds of the material are broken due to the transmission Of high-energy irradiance from
the laser pulse. After the short interaction, disintegrated atoms and molecules are
released from the surface, forming a plasma due to their high-energy states. The surface
Of the irradiated spot is heated by the high temperature plasma, which results in melting,
oxidation, and other thermal reactions. The thermal expansion of the high temperature
plasma induces propagation of stress waves, resulting the ejection of debris and

deposition of debris around the irradiated spot.

62

4.1.3. Irradiation in vacuum condition

A vacuum chamber was constructed to examine the laser interaction in vacuum.
A schematic diagram in Figure 27 shows the vacuum chamber, with quartz window for
transmitting excimer laser pulse, and an additional window for the focus-guiding laser.
Using a rotary-vane vacuum pump, a low vacuum condition (10.2 KPa) was gained in the
chamber. The vacuum chamber was placed on the x-y-z stage of the imaging system.
Series of SEM micrographs in Figure 30 are taken from the irradiation under vacuum
condition. In Figure 30a, the PAZ, around circular spot at the center, was considerably
reduced as compared to the Figure 28a in atmospheric environment. However, in Figure
30b, surrounding around the irradiated spot still show the PAZ. Even though the material
ejection from the silicon substrate was not observed in this condition, the edges of the
spot are blurred and spoiled by the plasma damage. The areas around the PAZ, indicated
by 1, 2, and 3, are magniﬁed and observed in Figure 30b-1, 6b-2 and 6b-3, respectively.
In Figure 30b-1, the edge of the spot did not show the ejection of the silicon substrate,
however, droplet-like precipitates are observed near the crater. In Figure 30b-2,
signiﬁcant amounts of the droplets are extensively observed in the PAZ. In Figure 30b-3,
the damages on the diamond ﬁlm appear somewhat different from those of the inside. In
Figure 30c, the tilted image shows that the surface of the crater is relatively even. NO
melting of the silicon substrate is also observed at the spOt, however, the blurred spoiled

are prominent.

63

300 um

 

Figure 30. SEM micrographs showing excimer laser irradiation in the vacuum condition;
a) the irradiation spot and surrounding, b) the irradiation spot with distinctive
zones marked by 1, 2, and 3, c) highly tilted (75°) image for the irradiation
spot, b-l) magniﬁed view of zone 1 from the ﬁgure b, b-2) magniﬁed view of
zone 2 from the ﬁgure b, b-3) magniﬁed view of zone 3 from the ﬁgure b.

 

Figure 31. Near spot edge area showing the plasma affected zone in the vacuum
condition.

The PAZ near the spot edge is shown in Figure 31, in which the debris shows both the
droplet-type deposition, and spread-type deposition.

In Figure 32, the part of the PAZ is magniﬁed to show that the droplets are
formed out of the spread-type debris deposition of the diamond ﬁlm. As the number of
laser pulse increases to ablate the ﬁlm surface, more carbon debris are deposited near the
irradiation spot, where the diamond crystals are suffering intense heating from the
expanding plasma. The accumulated debris are affected by the heat and shock wave from
the plasma, and formed droplets due to their high surface tension. Rapid solidiﬁcation

follows after the plasma is dissipated in the chamber.

65

 

Figure 32. Plasma affected zone in the vacuum condition showing the formation of the
debris droplets.

The dispersion of the plasma is faster in the low-pressurized medium [71]. Even
though some damage was found in the wake of expanding plasma, the area near the
irradiation spot showed the reduced PAZ, due to the rapid dispersion of the plasma. The
vacuum condition showed quite different morphology Of the PAZ due to the lack of

oxygen or other reactive gases.

4.1.4. Irradiation in gas-streaming condition
In the gas-streaming condition, a single nozzle was installed to blow a 99.9 %
argon gas over the surface of the diamond thin ﬁlm, upon the laser pulse irradiation. To

blow an inert gas, the nozzle was positioned about 3 cm from the irradiated spot and 30°

66

degrees to the ﬁlm surface. Diameter of the nozzle was 2 mm and the argon gas ﬂow rate
was 5x104 m3/sec.

A series of SEM micrographs in Figure 33 are taken from the irradiation in gas-
stream condition. In Figure 33a, no plasma affected zone was observed around the
circular spot at the center, in contrast to the cases in the ambient air and the vacuum
conditions. In Figure 33b, areas near the irradiated spot show no visible damage,
however, a close Observation revealed slight imperfections along the direction (arrows) of
the gas stream. The arrows indicate the direction of the argon gas stream, which gives
rise to the regional differences, marked by 1, 2 and 3 on the micrograph. The areas
indicated by 1, 2, and 3 are magniﬁed and observed in Figure 33b-1, 9b-2 and 9b-3,
respectively. Since the argon gas stream passes from area 1 to area 2, the area 1 in Figure
33b-l shows intact diamond crystals. In contrast, area 2 in Figure 33b-2 shows light
damage on the crystal surface. The light damage was caused by the bent plasma, which
was blown by the gas stream. The wake of the bent plasma causes light damages in near
edge area as show in Figure 33b-3. In Figure 33c, the crater is observed by a high-angle-
tilting in SEM. The crater shows the ﬂattest surface among the processing conditions.
The irradiated spot shows sharp and clean edges throughout all micrographs in Figure 33.
In Figure 34, partially ablated diamond crystals are shown at the edge of the spot. The
laser-sectioned crystals, in sizes of 2 pm ~ 5 pm, retain their original appearances, which
show the feasibility of the micromachining in micron and sub-micron range. One of the
slightly damaged diamond crystals is magniﬁed in Figure 35, which shows light

deposition of the ablation-debris on the edges and comers of the crystal.

67

5 um

50 um

u“ .a'

50 um - 5 I'm

 

Figure 33. SEM micrographs showing excimer laser irradiation in the argon gas-
streaming condition, a) the irradiation spot and surrounding, b) the irradiation
spot with areas marked by 1, 2, and 3, arrows indicate gas stream direction, c)
highly tilted (75°) image for the irradiation spot, b-l) magniﬁed view of area
1 from the ﬁgure b, b—2) magniﬁed view of area 2 from the ﬁgure b, b-3)
magniﬁed view of area 3 from the ﬁgure b.

68

 

Figure 34. Edge of the irradiation spot showing ablation-sectioned diamond crystals in
the argon gas streaming condition.

 

Figure 35. Light deposition of the ablation-debris on the edges and comers of the
diamond crystal in the argon gas streaming condition.

69

I
284nm x 189nm

 

Figure 36. Surface topographies of the irradiation spots of the diamond ﬁlm in the
different processing environments; a) ambient air, b) vacuum condition, and c)
argon gas-streaming condition. The topographies were taken by a confocal
laser scanning microscopy.

Surface topographies of the irradiated diamond ﬁlm are compared in Figure 36.
The topographic depth proﬁles were obtained by the confocal laser scanning microscope.

In Figure 36a, the ambient air exhibits the deepest average crater depth (12 pm) with the

70

most uneven crater surface. It also shows the severe damages at the spot edges and
surrounding. The surface roughness was improved under the vacuum condition, as
shown in Figure 36b. Accordingly, the average crater depth is reduced to 5.5 pm.
However, the blurred spot edges are extensively observed due to the plasma damages. In
Figure 36c, the gas-stream condition shows the most optimum irradiation on the diamond
ﬁlm. Measured average crater depth is 4.5 pm. The sharp spot edges and even crater
surfaces are remarkable in the image.

When the argon gas stream is passing over the irradiated spot, it dissipates the
high temperature plasma off from the surface, reducing the plasma-material interaction.
The gas steaming not only blows the ablated particles away, but also effectively quenches
the surrounding. Even though the slight imperfections were found in some portions of
the near-edge areas, overall feasibility of the gas-stream condition is good for the
micromachining of diamond ﬁlms.

Based on the observed gas-streaming effects, the gas delivery unit in the MP-I
system was designed. The gas delivery unit has three nozzles in a triangular geometry,
which can prevent the plasma bending and following imperfections in the single nozzle
streaming. Details are discussed in Chapter 2. With the three-nozzle gas delivery,
helium gas was also considered for the inert gas-streaming in further studies in later _
chapters. However, the vacuum condition was excluded due to the complexity caused by

the vacuum chamber and the limitation on the target translation for the 3D structuring.

71

4.2. Parameters of Laser-Diamond Coupling

4.2.1. Excimer laser ablation rate of CVD diamond films

The ablation by pulsed lasers depends on laser wavelength, laser irradiance and
absorptivity of the target material. The absorptivity is a material constant, which depends
on the material properties, such as heat capacity, latent heat Of evaporation, thermal
conductivity and density [14]. The ablation rate is an important parameter to predict

depth or mass removal rate for the pulsed laser-based micromachining.

4.2.I-a. Experimental setpp for the rate meapprements

The ablation rate of the CVD diamond ﬁlm was obtained by measuring the
ablation depth as a function of the number of laser pulses and the laser irradiance. The
measured ablation rates were compared among the gas processing conditions, such as the
ambient air, helium gas-streaming and argon gas-streaming. Figure 25 shows the
schematic diagram of the excimer laser setup for the rate measurements. The laser used
in the system is the KrF excimer laser (Lambda Physik®, model COMPex 301) with a
wavelength of 248 nm, a rectangular pulsed beam of 1.3x3.0 cm2 in TEMoo mode, a
maximum pulse energy of 1.5 J and a maximum repetition rate of 10 Hz. The rectangular
pulsed laser beam from the resonance passes through the 2.2 mm pin-hole aperture, and

then the circular beam is focused by two planar convex lenses in focal lengths 295 mm

and 50 mm, respectively.

72

 

 

 

 

 

 

 

REFLECTOR ‘3
1~K PLANAR CONVEX FL: 295 mm
GAS
Ham
PLANAR CONVEX FL: so mm

 

 

__.I.‘._,_....o.....

Figure 37. Schematic diagram of the excimer laser setup for the ablation measurements.

The focused spot size on the diamond ﬁlms was 175 um. Three gas nozzles are installed
around the Objective lens to deliver dynamic gas streaming over the irradiation spot. The
nozzles are positioned about 3 mm from the irradiation spot and 30° degrees to the ﬁlm
surface. The diameter of gas nozzle is 2 mm and the gas ﬂow rate is held constant at
5x104 m3/sec. Details about the three-nozzle gas delivery unit are discussed in Chapter
3. The diamond ﬁlms used in this investigation were hetero-epitaxially grown, on single
crystal silicon wafers, by the microwave plasma assisted CVD. The average grain size
and vertical thickness of the diamond ﬁlms were 10 um and 35 pm, respectively. The

diamond ﬁlm was subjected to the three gas processing environments, such as ambient

air, helium gas-streaming and argon gas-streaming.

73

The average ablation depth was measured by the confocal laser scanning
microscope (LSM), Zeiss 210, using the optical z-sectioning. The confocal images were
taken from all irradiation spots under various processing conditions, and then linear
proﬁles of the spots were recorded. Figure 38 shows examples of the scanned images
from an irradiation spot for the depth proﬁle. The confocal image of the irradiation spot
is shown in Figure 38a, and its linear depth proﬁles are shown in Figure 38b and c. The
linear proﬁles were compared with the topographic depth proﬁles for average values.
The topographic depth proﬁles were Obtained by the optical z-sectioning of the surface
topography. An example Of the series of the topographically z-sectioned images from an

irradiation spot is shown in Figure 39, in which the bright areas indicate the image planes

in focus with the listed depth values.

4.2.] -b. Ablation rate of CVD diamond ﬁlm

The diamond surface was irradiated up to 200 laser pulses to measure the ablation
rate as a function of the number of laser pulses. The pulse repetition depth and the laser
irradiance were held constant at 2 Hz and 6x108 W/cmz, respectively. Figure 40 shows
ablation depths as a function of number of laser pulses. The ablation rates are compared
among the gas processing environments, such as ambient air, argon gas streaming and
helium gas streaming. An approximately linear relationship was observed in the range
monitored between the ablation depth and number of laser pulses. At the initial stage of
the laser ablation, indicated by the arrow between 0 and 20 laser pulses, a slightly higher

ablation rate is observed due to the rough surface morphology of the polycrystalline CVD

diamond ﬁlm.

74

 

(b) linear depth profile

ZZXY=1 DZ=31.7 um

 

 

(c) high-resolution profile

Figure 38. Depth proﬁle measurements of the irradiation spot by the confocal laser
scanning microscope; a) confocal image of the irradiation spot, b) linear depth
proﬁle across the spot from the inset b in the ﬁgure a, and c) high-resolution
linear proﬁle near the spot edge from the inset c in the ﬁgure a.

 

175 um

       

d= 5.86 pm

    
     

d= 1.95 pm

     

d= 7.81 pm

 
 
    

d= 15.62 pm

      

 

 

  
    

 

 

 

d= 23.42 pm d= 25.38 pm d= 27.33 pm d= 29.28 pm
Figure 39. Topographic depth proﬁle of the irradiation spot by optical z-sectioning of
the surface topography.
so
25 _ I ambient air
0 Ar stream

He Stream

20 —

ablation depth (pm)
a:
I

n n 1 A I . l . l . l . l . l . l . I .
I 20 40 60 80 100 120 140 160 180 200
number of laser pulses

 

 

 

Figure 40. Ablation depth as a function of the number of laser pulses on the CVD
diamond ﬁlm.

76

40

 

 

 

 

 

 

I ambient air
35 0 Ar stream
A He steam
E 30 -
i
'D
.5 25 -
E
8
20 P
15

 

 

 

1 0
laser irradiance (X10' W/cmz)

Figure 41. Ablation depth as a function of the laser irradiance on the CVD diamond ﬁlm.

No signiﬁcant difference was found on the ablation rate among the gas processing
environments. The average ablation rate of 0.14 urn/pulse was obtained from the linear
relationship.

The ablation rate as a function of the laser irradiance was also measured by
varying the laser energy ﬂuence from 2.4X108 W/cm2 to 8.4x108 W/cmz, with a constant
number of laser pulses at 200 times and a constant repetition rate at 2 Hz. The plot of the
ablation depth versus the laser irradiance is shown in Figure 41. The monitored range of
the laser energy ﬂuence was set between the ablation threshold (~ 108 W/cm2 [17, 18] ) of
diamond ﬁlm and the maximum energy output of the laser used in this investigation.
The increase in the ablation depth as a function of the laser irradiance is approximately
linear in the range observed in this study. The gas processing environments did not

signiﬁcantly alter the ablation rate. The slope of the plot, ablation depth versus the laser

77

irradiance, represents the coefﬁcient of laser energy absorption 1' (cm3/W). This
coefﬁcient is a material constant, which depends on the physical properties of the
material, such as heat capacity, latent heat of evaporation, thermal conductivity, density,
and surface reﬂectivity [14]. The 1' also indicates the volume removal rate, which is

essential to the modeling of the ablation process.

4.2.] -c. Modeling for the depth ablation

In this study, the linearity found in the ablation depth versus the pulse numbers

(Figure 40) and the laser irradiance (Figure 41) gives the relationship:

dzr-n-I Equation9

where d is the ablation depth (um), I is the coefﬁcient of laser energy absorption
(cm3/W), n is the number of laser pulses, and I is the laser irradiance (W/cmz). This
equation assumes that the laser irradiance is steady through the ablation process; hence,
the depth ablation rate stays constant. It also assumes that the linearity exists in the
observed laser irradiance range, which is relatively small for the possible irradiance rages
for the ablation of diamond ﬁlms.

Even though the approximation of linearity was reasonable in the relatively small
depth range observed in this study, the nonlinearity exists due to the divergence of the
focused laser beam. When the divergence of the focused laser spot is taken into account,
nonlinear relationship has to be considered for the ablation depth as a function of the

number of laser pulses.

78

LASER BEAM

PLANAR CONVEX LENS

 

 

l FOCAL POINT

 

 

 

 

Figure 42. Schematic diagram for the laser irradiation with divergent laser beam.

Figure 42 shows the schematic illustration in which the laser irradiation with
circular beam on a ﬂat surface was supposed. The initial radius r,- at the initial target
surface, i.e., at the image plane, is diverged to the final radius r; after the ablation depth d.
The divergence angle a is the angle between the edge Of the cone of the laser irradiation
and the vertical at the center of the circular beam spot. The ais also known as the angle
of the numerical aperture (NA), in which NA = nsina [72]. Where the 7] is the refractive
index of the medium in which the light passes through, and 7] = l in the air. The
numerical aperture in optics represents the light gathering power of a lens. From Figure

42, the relationship among the parameters can be written as:

r,. _2_ Equation 10

where the imaging distance l is the distance between the focal point of the lens and the
image plane on the initial target surface. From this relationship, the ﬁnal radius r, can be

written as:

f-d Equation 11

 

m} 2 2m? 2
= 72— + l +7”.- Equation 12

Substitute the initial spot size It);2 for A,- and express the diverged spot size as a function

of ablation depth d:

A(d) =[%}12 +(ZTA'}I + A. Equation 13

where A(d) is the spot size as a function of the ablation depth d. The initial spot size AI,
and the imaging distance I are the processing constants. Equation 13 shows that the
initial spot size A.- is gradually enlarged as the ablation depth d increases, and the size of
the diverged spot A(d) is the second order polynomial function of the ablation depth d.
Since the laser irradiance (W/cmz) is inversely proportional to the beam spot size, the

depth dependant laser irradiance [(d) can be written as:

W

I (d) = m Equation 14

80

From Equation 9, the ablation depth as a linear function of the number of laser pulses is:
d

" = :7 Equation 15
For the nonlinear divergence compensation, the laser irradiance I in this linear
relationship is substituted for the divergence dependent laser irradiance I(d).

Accordingly, the combination between Equation 14 and Equation 15 gives the nonlinear,

divergence compensated ablation depth as a function of the number of laser pulses:

n_d-A(d)
r-W

 

Equation 16

Combining with Equation 13 and rearranging for d give the pulse number n as the third

order polynomial function of the ablation depth d:

_. Al 3 2A: 2 At
n— e 2 + a o + a
r W-l r W l r W
A: (13 2d2
=—.— "2—+ +61
T W l l

_ 1 d3 2.12
———.— T'I' +d
r I, l l

 

 

 

 

Equation 17

where I,- is the initial laser irradiance from the relationship I,- = W/AI. In Equation 17, the
initial spot size A;, imaging distance I and laser power W are the processing constants,
which can be measured form the experimental setup for the laser irradiation. As
discussed in Section 4.2.1-b, the coefﬁcient of laser energy absorption 2' is the material
constant, and can be obtained from the slope of the plot of the ablation depth versus the

numbers of the pulses and the laser irradiance.

81

oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

ablation depth d

 

 

number of laser pulses n

Figure 43. Ablation depth d as a function of the number of laser pulses n according to the
Equation 17.

With the measurable processing constants, the ablation depth can be predicted by the
number of laser pulses in Equation 17. This equation accounts the divergence of the
focused laser beam, which results in the nonlinear decrease in the laser irradiance.
According to Equation 17, the ablation depth is shown as a function of the number of
laser pulses in Figure 43. Due to the depth dependant laser irradiance I(d), gradual
decrease in ablation rate (Ad/An) is expected as the number of the laser pulses increases.
The lower boundary of the plot is where n = d = 0, and upper boundary is the point
where the depth dependent irradiance I(d) drops below the ablation threshold of the target
material. In the ablation process with the same material and optics setup, i.e., constant 2’
and l, the curvature of the line is mainly depends the initial irradiance I.-, as show in the

graph.

82

Table 8. Measured processing parameters for the nonlinear ablation depth modeling.

 

 

 

 

 

divergence angle at 3° degree
initial spot size A, 2.40x104 cm2
imaging distance I 0.167 cm
absorption coefﬁcient r 2.305x10’l4 cm3/W
initial irradiance I; 6><108 W/cm2

 

 

 

 

The ablation with higher initial laser irradiance reaches its upper boundary, i.e., ablation

threshold due to the beam divergence, faster than the ablation with lower initial laser

irradiance.

4.2. I -d. Prediction of the ablation depth

The modeled equation for the nonlinear ablation rate is applied to the
experimental data acquired in Section 4.2.1-b. The processing parameters were measured
from the experimental setup in Section 4.2.1-a and the acquired data in Section 4.2.1-b.
The measured processing parameters are shown in Table 8. Using these parameters,

Figure 44 shows the modeling of the ablation depth as a function of the number of the
laser pulses. Since the subjected diamond ﬁlm has the small average thickness of 35 pm,
the prediction of the ablation depth was extended up to 1000 pm by the modeling. The
linear function was plotted based on Equation 9 and the nonlinear function was plotted
based on Equation 17. The enlarged box in Figure 44 shows the predicted ablation
depths by both the linear and nonlinear functions in the ablation depth region less than ~

50 um. In the small ablation depth range, the differences between the linear and

nonlinear functions were less than ~ 5 %.

83

 

 

 

 

 

 

 

 

1 000 - LI EAR N LINEAR
800-
‘E‘ 50', LINEAR
S
_ 40-
b 600 , NONLINEAR
.C
a I 30-
.8 .
400-
.5 20‘
a '1
'5 to-
It! 200_ .............. v 4
---------- o 2 e . .
. .............. o 100 200 300 400
0 = . r E . . , . .
o 5000 10000 15000 20000

number of laser pulses n

Figure 44. Modeling of the ablation depth as a linear function of the number of the laser
pulses, and as a nonlinear function of the number of the laser pulses (at the

initial laser irradiance 6x108 W/cmz).

However, in the ablation depth range close to 1000 pm for deep drilling or high aspect
ratio micromachining, the required number of laser pulses is almost tripled in the
nonlinear ablation depth prediction, as compared to that in the linear function. Similarly,
the predicted ablation depth with 2x104 pulses is 2800 pm for the linear function, but
only 1000 pm for the nonlinear function. The discrepancy between the linear and
nonlinear functions is exponentially increased as the number of laser pulses increases.
The modeling for the divergence compensation showed that the approximation of
the linearity in this study was reasonable in the range of the ablation depth less than ~ 50
pm. In this range of ablation, no signiﬁcant reduction of the ablation depth was expected
due to the negligible divergence of the laser beam. The degree of the beam divergence,

consequently the reduction in the depth ablation rate, mainly depends on the optical setup

84

of the ablation process. In optics, the larger value of NA results in the greater beam
divergence [72]. In the optics setup in this study, we have chosen a small numerical
aperture, NA: 5.23x10'2 (at: 3°). In the observed range of ablation depths up to ~35 pm
in this study, the calculated loss of the laser energy is less than 2.5 % of the initial

irradiance, which is insigniﬁcant to exhibit nonlinearity on the monitored range.

4.2.1 -e. Veriﬁcation of the modeling

The prediction of the ablation depth is essential for the precision micromachining,
especially for the deep ablation for the high-aspect-ratio features. The proposed
nonlinear modeling was veriﬁed by subjecting a thick diamond ﬁlm for the ablation

depth measurement. The thick CVD diamond ﬁlm, average thickness 270 um and

average grain size 40 um, was used to allow enough ablation depth for the deep ablation.
The silicon wafer substrate, where the CVD diamond ﬁlm was grown by the hetero-
epitaxial growth, was completely dissolved in the etching solution (50%HNO3 + 25%HF
+ 25%CH3COOH) to acquire a freestanding diamond ﬁlm. The substrate side of the
freestanding diamond ﬁlm, which retained ﬂatness similar to the polished silicon wafer,
was exposed to the laser irradiation. The same experimental setup described in Section
4.2.1-a was used for the laser irradiation. The diamond surface was irradiated by up to
2000 laser pulses to measure the ablation depth as a function of the number of laser
pulses. The pulse repetition rate and the laser irradiance were held constant at 10 Hz and
6x108 W/cmz, respectively. For the modeling of the ablation process, the processing

parameters were measured and tabulated in Table 9.

85

Table 9. Measured processing parameters for the nonlinear ablation depth modeling.

 

 

 

 

 

divergence angle at 3° degree
initial spot size A; 2.40x104 cm2
imaging distance I 0.167 cm
absorption coefﬁcient 1' 2.661x10'14 cm3/W
initial irradiance 1, 6x108 W/cm2

 

 

 

 

The measured absorption coefﬁcient r(2.66l><10'14 cm3/W) was close to that of the other
diamond (2.305x10'” cm3/W) ﬁlm measured in Table 8. Using these parameters, the
linear function was modeled, based on Equation 9, and the nonlinear function was
modeled based on Equation 17. Figure 45 shows the modeled linear, modeled nonlinear

and experimentally measured ablation depths, which are plotted as a function of the

number of laser pulses.

Unlike the laser irradiation on the rough polycrystalline diamond surface (see
Figure 40), the irradiation on the ﬂat surface of the freestanding diamond ﬁlm did not
exhibit the high initial ablation rate. In the measured ablation depth, the onset of the
nonlinearity was observed near ~ 120 pm by ~1000 number of pulsed irradiation. The
trend line of the measured ablation depth showed slightly higher curvature than that of
the modeled nonlinear ablation depth. The higher curvature in the plot results in the lower
ablation depth at the same number of pulsed irradiation. The lower ablation depth from

the experimentation might be due to the conﬁnement of the laser-induced plasma in the

deep-dilled holes.

86

MODELED

200 7 MODELED NONFINEA" MEASURED
180-

160 -

140-

120-

ablation depth d (pm)
8
l

 

 

 

80...

60-
'1

40-

20-

O r r E I r I I 1' I' I
0 500 1000 1500 20m) 2500

number of laser pulses n

Figure 45. Ablation depth as a function of the number of laser pulses on the thick
diamond ﬁlm.

In the laser ablation process, the laser-induced plasma contains the ablated carbon
particles, which are ejected to the ambient together with the expanding plasma [27]. The
trapped plasma in the deep-drilled hole causes the redeposition of the ablation particles in

the hole. The redeposition reduces the depth ablation rate upon the laser irradiation.

87

4.2.2. Laser-diamond interaction

Carbon exists in a few solid-state phases in the atmospheric condition. Diamond
and graphite are well-known solid-state phases. Diamond of sp3 bonding is optically
transparent, electrically insulating and chemically inert [73]. In contrast, graphite of spz
bonding is optically opaque, electrically conductive, and chemically reactive [41].
Application of heat and pressure transform the carbon phase between diamond and
graphite.

The UV excimer lasers are suitable for the ablation processing of diamond ﬁlms
due to the high optical absorption in the UV range. The magnitude of the ablation is
determined by the laser wavelength and irradiance, and the Optical absorptivity and other

properties of the target material [14, 74].

1.2224. Diamond to graphite phage tranjomﬁon

The phase transformation from diamond to graphite has been reported upon the
irradiation by the various pulsed lasers on CVD diamond ﬁlms [15, 16, 18, 21, 24, 75].
The diamond to graphite transformation was inevitable in the laser irradiation in this
study, in which the KrF excimer laser with 248 nm wavelength and 25 ns pulse duration
was source of the irradiation. Regardless of the gas processing conditions, the laser
irradiation resulted in the diamond to graphite transformation on surface layers. The
structural transformation was detected by extinction of the diamond spectrum in the
Raman spectroscopy. A thick CVD diamond ﬁlm, average thickness 110 um and
average grain size 50 um, was subjected to 20 pulses of the laser irradiation with the laser

irradiance of 4x108 W/cm2 and the repetition rate of 1 Hz. In the Raman spectroscopy,

88

the monochromatic light source (Argon laser at 514.5 nm, 300 mW) was illuminated on
the diamond ﬁlm to detect the Raman peak shift. By comparing before and after the laser
irradiation, Figure 46 shows the extinction of the diamond Raman spectrum (1332 cm")
by the structural transformation.

In the carbon phase diagram, the CVD diamond exists in the metastable state of
the graphite region [3]. The CVD diamond surfaces are reconstructed to graphite at the
temperature region over 900°C. The phase transformation was mainly caused by the heat
and pressure, which are created by the absorption of the laser energy and propagation of
the plasma-induced shock waves [16, 75]. The surface heating by the laser irradiation
results in the surface reconstruction from sp3 bonded metastable diamond to the sp2
bonded stable graphite conﬁguration [4].

The evidences of the laser-induced diamond-graphite transformation led to the
close examination on the evolution of the polycrystalline diamond surface morphology
upon the laser irradiation. The evolution of the surface morphology, at the initial stage of
the laser—diamond interaction, was observed by the atomic force microscope (AFM),
Digital Instrument Nanoscope IIIa in TappingmodeQ. The thin diamond ﬁlm (BW062)
with a small grain size was selected for the AFM observation. The average grain size and
vertical thickness of the subjected diamond ﬁlm was 2 pm and 4 pm, respectively. The
diamond ﬁlm was irradiated by the laser irradiance of 4x108 W/cm2 with 1, 3, 6 and 10

laser pulses.

89

   

(a) before

 

2500 —

2000-

1500 -

1000-

 

intensity (arbitrary unit)

500 BEFORE
AFTER

 

 

 

0 ' .
1200 1300 1400 1500 1600

 

wavenumbers Shift (cm")

(C) Raman spectroscopy

Figure 46. Extinction of the diamond Raman spectrum (1332 cm!) by the excimer laser
irradiation; a) before the laser irradiation, b) after the laser irradiation, and c)
Raman spectrum.

90

The same experimental setup described in Section 4.2.l—a was used for the laser
irradiation. The spot size on the diamond surface was 80 um.

Figure 47 shows the evolution of the surface morphology by the laser-diamond
interaction. In Figure 47a, the unexposed surface shows sharp edges of the truncated
{100} diamond crystalline. In Figure 47b, a preferential interaction was observed in
which the sharp edges of the crystalline were chipped off by the single-pulse irradiation.
After 3 pulses of irradiation in Figure 47c, the surfaces of the diamond crystals started to
erode away. The sharp edges and vertexes of the diamond crystals were smoothened out
by the laser irradiation. In Figure 47d and e, the surface morphology kept evolving in
such a way as to gradually smoothen out the edges and vertexes.

The magniﬁed View of Figure 47 is shown in Figtire 48, which shows the
submicron features of the surface morphology. The preferential diamond-laser
interaction was noticed in Figure 48b that the edge of the diamond crystal (indicated by
the arrow) was chipped-Off by the laser irradiation. In Figure 48c, the evolution of the
surface morphology was continued, not by the preferential edge chipping-off mechanism
but by an overall smoothening-out mechanism. The signiﬁcantly smoothened surface is
observed after 10 times of the pulsed irradiation in Figure 48c.

From the observations in Figure 47 and Figure 48, it can be speculated that the
preferential interaction by the edge-chipping-off mechanism occurs at the very initial
stage with in 1 to 2 laser pulses. Then, the successive laser irradiation reduces the surface
roughness in overall smoothening-out mechanism. The preferential laser-diamond

interaction was observed in other type of the diamond crystals as well.

91

(a) 0 pulse (b)1 pulse

|~

(d)6pu|ses \_ -' _ » (e)10 pulses

 

Figure 47. AFM (Tappingmodem) observation on the evolution of surface morphology
by the excimer laser irradiation.

92

(a) 0 pulse (b) 1 pulse

 

Figure 48. AFM (T appingmode‘”) observation, in sub-micron scale, on the evolution of
surface morphology by the excimer laser irradiation.

93

 

 

 

 

 

 

1332
25001
2000--
re
c
3
g 1500-
59.
g 1000-I
.‘E
500- Opulse .
1 pulse
over3pulses
o T I I I I I I
1200 1300 1400 1500 1600

wavenumber (cm")

Figure 49. Observation of the Raman spectrum on the excimer laser irradiated diamond
surfaces.

The observation of the Raman spectrum is shown in Figure 49 for the laser
irradiated diamond surfaces. The single pulse irradiation in Figure 48b still exhibited
some extent of the diamond spectrum, indicating that the surface was not entirely
graphitized. Over 3 pulses of the laser irradiation, the surface completely lost the
diamond spectrum. Hence, it is conclusive that the laser-diamond interaction causes the
formation of an opaque graphitized surface layer within few pulsed irradiations. Then,

the self-sustaining graphite layer absorbs the successive laser pulses, and the surface

morphology evolves according to the ablation [l8].

94

4.2.2-b. Evolution of sudace momhology

To examine the evolution of the surface morphology beyond the initial
interaction, a set of in-situ observations were performed on the CVD diamond ﬁlm. The
ESEM (Philips Electroscan 2020) was used for the in—situ observation of the evolution of
the surface morphology. The acceleration voltage used in ESEM was 20 kV. The thick
diamond ﬁlm (thickness: ~ 110 pm) with large grain size (average grain size: ~ 50 mm)
was selected for the macroscopic observation. The diamond ﬁlm was irradiated by the
laser irradiance of 6x108 W/cm2 with 5, 20, 50, 100 and 200 laser pulses.

Figure 50 shows the macroscopic evolution of the surface morphology upon the
laser irradiation. The arrows in Figure 50 indicate the same location through out the
gradual exposures to the laser irradiation. After 5 times of the laser pulses in Figure 50b,
the sharp edges of the diamond crystals are lightly etched by the irradiation. In Figure
50c and d, the edges and vertexes of the diamond crystals are gradually smoothened out,
as the pulsed irradiation increased to 20 and 50 times. In Figure 50c, the uneven etching
on the diamond surface signiﬁcantly diminished the outlines of its original morphology.
The rough surface in Figure 50a is entirely smoothened out in Figure 50f by 200 laser
pulses. Figure 51 also shows the roughness reduction in larger area after 200 laser

pulses. As shown in Figure 50b ~ e, the in-situ observation revealed that the roughness

reduction occurred by the uneven etching of the crystalline surface.

95

 

 

 

 

Figure 50. ESEM in-situ observation on the evolution of the surface morphology of the
laser irradiated diamond surface; a) 0 pulse, b) 5 pulses, c) 20 pulses, d) 50
pulses, e) 100 pulses, and f) 200 pulses. The arrows indicate the same
position throughout the observation.

96

 

100 um 100 um

 

Figure 51. Roughness reduction of the polycrystalline diamond surface by the excimer
laser irradiation; a) before the laser irradiation, and b) after 200 laser pulses at
6x108 W/cmz.

The sharp edges and vertexes exhibited higher etching rate than that the planes and
valleys. The uneven etching ratio can be qualitatively explained by the overheating of
the crystal edges and vertexes. Upon the laser irradiation, the absorbed laser energy heats
the surface. The spread of heat is uneven when the target surface is rough. The
protruded features such as edges and vertexes are overheated by the uneven spread of the
heat [18]. The vapor screening by the laser—induced plasma also promotes the
overheating of the surface features. The laser-diamond interaction causes, within few
pulses, the formation of the self-sustaining amorphous graphite micro-layer. In Figure
52, the cross sectional view of the diamond ﬁlm shows the formation of the graphite
micro-layer. The self-sustaining graphite layer absorbs the energy from following laser
irradiations, and determines the evolution of the morphology by the uneven etching on

the surface.

97

GRAPHITE MICRO-LAYER

SI SUBSTRATE

 

50 um

 

Figure 52. Formation of the self-sustaining graphite micro-layer upon the excimer laser
irradiation by 200 pulses of irradiation at 6x108 W/cmz.

4.2.2-c. Removal at graghite layer

To examine the environmental effects of the laser irradiation, the diamond ﬁlm
was subjected to the three different gas-processing conditions, such as ambient air,
helium gas-streaming, and argon gas-streaming. The average grain size and vertical
thickness of the diamond ﬁlms were 10 um and 30 pm, respectively. The laser irradiance,
repetition rate, number of pulses, and gas flow rate were ﬁxed at 6><108 W/cmz, 2 Hz, 200
times and 5x104 malsec, respectively. A circular beam spot of 175 um in diameter was
illuminated on the ﬁlm surface by the excimer laser imaging system. The rapid
transmission of high laser energy ﬂuence causes disintegration of atomic bonds of the

CVD diamond. After the short interaction, disintegrated atoms are released from the

98

surface, forming plasma due to their high-energy states [16]. This results in deposition of
debris around the irradiated spot, and the explosive expansion of the plasma induces the
propagation of stress waves [27]. The ESEM was used to observe surface morphologies
of nonconductive CVD diamonds. Regardless of the gas processing conditions, the laser
irradiation resulted in the formation of the amorphous graphite micro-layer on the
surface. However, the interaction between the CVD diamond and the excimer laser
pulses showed quantitatively and morphologically different deposition of ablation debris
among the gas processing environments.

The group of micrographs in Figure 53 shows the ﬁlm morphology around the
irradiation spot. All processing environments show deposition of carbon debris, which
forms distinctive plasma affected zone (PAZ), around the irradiation spot. Near the spot
edges, the largest amount of debris deposition is observed with argon streaming in Figure
53c-1, while the ambient air shows the least amount of deposition indicated in Figure
53a-l. The morphologies of deposited carbon debris are also different among the
processing conditions. The origins for the quantitative and morphological differences of
the carbon debris are discussed in Chapter 5. The graphite layers and deposited particles
are chemically removed by boiling (~ 200°C) in 1:1 solution of GO; and H2804 for 2
minutes. The solution is known for its dissolving ability of graphite [75]. After the
cleaning, the irradiation spots are observed in Figure 53a—2, b-2 and c-2. In these ﬁgures,
no visible residue of deposited carbon debris was found in all processing conditions. The
helium gas-streaming (Figure 53b-2) and argon gas-streaming (Figure 53c-2) show no
obvious damage around their spot edges. In contrast, light damage is found around the

irradiation spot in the ambient air (Figure 53a-2).

99

 

 

 

 

Figure 53. Edges of the irradiation spots showing the carbon debris deposited by the
irradiation (left column) and cleaned edges by the removal of the deposition
(right column); a-l) ambient air - as irradiated, a-2) ambient air - after the
cleaning; b-l) helium streaming - as irradiated, b-2) helium streaming - after
the cleaning; c-l) argon streaming - as irradiated, c-2) argon streaming - after
the cleaning.

100

   

10 um

 

Figure 54. Damaged diamond crystals around the spot edge from the laser irradiation in
the ambient air; a) the damaged spot edge, the arrows indicate the damaged
area, b) magniﬁed view of the damaged area, indicated by the arrows.

Figure 54 shows the damaged diamond crystals around the spot edge, which is formed by
the laser irradiation in the ambient air. The arrows in Figure 54a indicate the extent of
damaged area near the irradiation spot. The damaged diamond crystals are magniﬁed in
Figure 54b, and the arrows also indicate the extent of the damaged area. The light
damage, around the irradiation spot in the ambient air, can be explained by the plasma-
diamond interaction, which results in over heating of area near the spot edge. In helium
gas-streaming and argon gas-streaming conditions, the dynamic streaming upon the laser
irradiation reduces the plasma-diamond interaction, resulting in intact diamond crystals

near the spot edge.

101

4.3. Chapter Summary

The laser-diamond interaction was examined by subjecting the diamond ﬁlm
under three different processing environments, such as the ambient air, the vacuum
condition and the gas-streaming condition. The interaction, between the CVD diamond
and the excimer laser pulses, showed drastic changes among the different processing
environments. The vacuum condition was ruled out due to the complexity caused by the
vacuum chamber and the limitation of the target translation in the chamber. By the
dissipation of the high temperature plasma off from the surface, the inert gas-streaming
showed a good feasibility for the precise micromachining of diamond ﬁlms. The gas
delivery unit, which has three nozzles in triangular geometry, was designed based on the
observed gas-streaming effects. With this gas delivery unit, further studies of the laser-
diamond interaction were performed in the ambient air, helium gas streaming and argon
gas streaming conditions.

The ablation rate of the CVD diamond ﬁlm was obtained by measuring the
ablation depth as a function of the number of laser pulses and the laser irradiance. The
measured ablation rates were compared among the gas processing conditions, such as the
ambient air, helium gas and argon gas, respectively. No signiﬁcant difference was found
on the ablation rate among the gas processing environments. Approximately a linear
relationship was observed between the ablation depth and the number of laser pulses, and
between the ablation depth and the laser irradiance. Based on these observations, linear
and nonlinear models for the ablation process were proposed. The nonlinear model

accounted for the divergence of the focused laser beam, and resultant decrease in the

102

laser irradiance. The nonlinear modeling proposed the number of the laser pulses as the
third order polynomial function of the ablation depth. The nonlinear model was veriﬁed
by the ablation on thick diamond ﬁlm. The experimentally measured ablation depth
showed slightly higher curvature than that of the modeled nonlinear ablation depth. The
origin of the discrepancy is assumed to be due to the trapped plasma in the deep-drilled
hole, which causes the redeposition of the ablation particles in the hole. The redeposition
made the experimental rate of depth ablation lower than the expected ablation rate from
the nonlinear modeling.

The initial stage of the laser-diamond interaction was observed by the AFM and
Raman spectroscopy. It could be speculated from the AFM observation that the
preferential interaction by the edge-chipping-off mechanism occurs at the very initial
stage with in l to 2 laser pulses. Then, the successive laser irradiation reduces the surface
roughness in overall smoothening-out mechanism. It was reasonably conclusive from the
Raman spectroscopy observation that the laser-diamond interaction causes the formation
of the graphitized surface micro-layer within a few pulsed irradiations. Then, the self-
sustaining graphite layer absorbs the successive laser pulses for the ablation, and the
surface morphology evolves according to the ablation.

To examine the evolution of the surface morphology beyond the initial
interaction, in-situ observation was performed for the laser irradiation on the CVD
diamond ﬁlm. The sharp edges and vertexes exhibited higher etching rate than the planes
and valleys. The roughness reduction was caused by the uneven etching on the jagged
polycrystalline diamond crystals. The uneven etching ratio is explained by the

overheating of the crystal edges and vertices due to the laser irradiation.

103

The removal of the graphite layers, and deposited particles were performed by
boiling the sample in the mixed solution of 003 and H2804. for 2 minutes. No visible
residue of deposited carbon debris was found after this chemical cleaning. The helium
gas-streaming and argon gas-streaming show no obvious damage around their spot edges.

In contrast, light damage is found around the irradiation spot in the ambient air.

Chapter V

LASER-INDUCED PLASMA ON CVD DIAMOND FILMS

5.1. Laser-Induced Breakdown Spectroscopy (LIBS)

5.1.1. Introduction to LIBS

Laser-induced breakdown spectroscopy is elemental analysis based on emission
spectra from plasma, generated by a powerful laser pulse on a sample. The laser-induced
breakdown spectrometry (LIBS) makes use of principles similar to those of conventional
plasma atomic emission spectrometry, in which the plasma is induced by various ways,
such as induction coupling, microwave, direct current, arc and spark [74, 76-81]. In
conventional atomic emission spectrometry, the spectral emission is obtained by
transportation of a sample to a plasma source for excitation. Consequently, sample
preparation and complex design of an excitation chamber are required in most cases. In
contrast, the LIBS utilizes pulsed laser ablation by optical radiation, which generates the
laser-induced plasma directly from the sample. This direct ablation makes in-situ
observation possible on emission spectra of gaseous, liquid, and solid samples without
the sample preparation [74, 82]. The direct observation of laser-induced plasma in LIBS

offers in-situ analyses on emission spectra of CVD diamond ﬁlms in various gas

processing environments.

5.1.1-a. generation at laser-induced plasma

104

105

Laser-induced breakdown is deﬁned as the generation of a practically totally
ionized gas, i.e. the plasma, at the end of pulsed laser irradiation [74, 78, 82, 83]. The
laser-induced plasma is formed when the laser energy irradiance exceeds the breakdown
threshold of a target material, where the irradiance is determined by laser power per unit
area (W/cmz). The laser-induced plasma is developed by the inverse bremsstrahlung
absorption, during collisions among vaporized atoms, ions, and electrons. The inverse
bremsstrahlung process is reverse of the bremsstrahlung process in which high-energy
electrons emit electromagnetic radiation as they slow down in media [74, 76, 78, 82-86].
In the bremsstrahlung process, accelerated electrons lose energy by elastic and inelastic
collisions with atoms and molecules. In the laser-induced plasma, electrons gain energy
much larger than that of ionization, when the laser energy irradiance is high enough. The
electrons in high-energy state generate new electrons by ionizing collisions. In spite of
the collisions, some of the new electrons retain energy over ionization, thereby leading to
cascade growth, the inverse bremsstrahlung process.

There are two main mechanisms for electron generation and growth by the inverse
bremsstrahlung [74, 78, 82, 83, 87]. The ﬁrst mechanism, called cascade ionization, is
associated with absorption of laser radiation by electrons that collide with neutrals.

When the electrons gain sufﬁcient energy, they can ionize the gas or solid neutrals

through the reaction,

e'+M —-)2e‘+M+ Equation 18

where, e is an electron, M is a neutral atom or molecule. This reaction leads to the
cascade breakdown, where the electron concentration increases exponentially with time.

The cascade breakdown requires existence of initial electrons at the laser irradiation to

106

gain excitation energy greater than ionization energy. Multiphoton ionization is the
second mechanism, which involves the simultaneous absorption of ionization energy
from a sufﬁcient number of photons. The multiphoton ionization is described by the

reaction,

M + nhv —-> M + + 6' Equation 19

where n is number of photons, h is Plank’s constant and v frequency. The ionization rate
is proportional to the laser irradiance, and increases linearly with time. The multiphoton
ionization is taken into account only when the incident laser pulse has a short wavelength
less than about 1000 nm. For an example, the simultaneous absorption of more than 100
photons is required for the C02 laser (,1 = 10.6 um, hv = 0.11 eV) to ionize a carbon atom
(ionization energy = 11.26 eV). In contrast, the KrF excimer laser (2 = 248 nm, hv =
5.01 eV) requires only about 2 photons to ionize the carbon atom. Using the excimer
laser of a short wavelength is far more probable for the ionization of the carbon.

The laser-induced plasma, especially for short wavelength lasers, is generated by
combination of the two ionization mechanisms. The initial electrons are created by

multiphoton ionization, and the initial electrons induce cascade ionization by the

bremsstrahlung absorption.

5.]. I -b. Characteristics of Laser-induced plasma

The temporal evolution of the laser-induced plasma on a solid target is
schematically illustrated in Figure 55 [18, 74, 82, 83, 88]. The diagram is based on 25 ns
laser pulse duration for the KrF excimer laser and the laser irradiance over ablation

threshold of a solid target.

107

 

 

 

 

 

 

L IONS _|
IT 'I
.A ATOMS A.
“—j IT 'I
903-; LASER PULS L MOLECULES _
a " '
.E
C
.9
I!)
.2
E
0
(5
g
as
Q
I l I I
1ns tons 100ns 1us tons 100us

time
Figure 55. Schematic diagram for the temporal evolution of the laser-induced plasma,
illustrating various regimes of the emission spectra. 25 ns laser pulse duration

of KrF excimer laser and irradiance over ablation threshold were assumed [18,
74, 82, 83, 88].

At the beginning of the ‘laser pulse’ regime, the leading edge of a laser pulse starts to
interact with the solid target. Consequently, the absorbed laser energy rapidly heats the
surface layer to instantly vaporize the solid. During the heating of the surface layer,
partial loss of the absorbed energy is caused by the latent heat of fusion and evaporation,
and heat sink to the bulk by thermal conduction. The initial ionization is mainly achieved
by the multiphoton absorption process [18, 83, 87], which release high-energy free
electrons from the target surface. The early vapor-phase species interact with the trailing
edge of the incident laser pulse and absorb up to 20% of energy from the laser pulse [88].
This interaction aids some internal ionization of the early vapor-phases. Collisions

among the charged particles also lead to increase in temperature and pressure of the

108

initial plasma. However, absorption of the incident laser energy, which results in thermal
ionization, is the main mechanism for the generation of initial plasma in the ‘laser pulse’
regime. At the onset of the plasma, the emission spectra start to display continuum
background, indicating the rapid heating.

In the ‘ions’ regime, the process of evaporation by the absorbed laser energy
continues, and the electron density of the partially ionized vapor becomes high enough to
propagate the inverse bremsstrahlung process. The ionization of the plasma is drastically
increased by the onset of the inverse bremsstrahlung process, which exponentially
increases the electron density of the plasma as a function of the time [78, 83-86]. The
increased density of the excited electrons sharply elevates the plasma temperature.
Multiply ionized, highly kinetic species are generated, and then these energetic particles
expand ballistically to the ambient. Continuous growth and heating of the plasma at high
temperature and high electron density make the plasma extremely high in energy density.
The temperature of the plasma near the irradiation surface reaches to the order of 104 to
105 [68-70, 89-91]. This causes the explosive expansion of the plasma, which sustains its
luminosity up to 100 us in duration [27, 78, 83]. The electron density as well as the
temperature sharply drops with the expansion of the plasma to the ambient. Until the
plasma reaches its peak density and temperature, the inverse bremsstrahlung process
continuously increases the continuum background of the spectral emission. When the
plasma explosively expands, the recombination between multiply ionized particles and
electrons forms the lower level ions, and the recombination releases continuum emission
spectra [74, 78]. In the recombined ions, subsequent relaxation of the excited electrons to

the ground state generates the characteristic ionic spectra [79, 92, 93].

109

In the ‘atoms’ and ‘molecules’ regimes, the expansion of the plasma causes
continuous decrease in the electron density. The electrons lose their energy and
recombine into ions to form neutral atoms and subsequent molecules. The valuable
atomic and molecular emission spectra are obtained in theses regimes when the excited
electrons of the neutral particles release their energy by returning to the ground state [93,
94]. The laser-induced plasma interacts with its surrounding during expansion [78]. The
expansion of the high-pressure and high-temperature vapor drives shock waves into the
target and atmosphere. As the radially expanding plasma sweeps across the target,
thermal conduction and radiation across the thin boundary layer can transfer signiﬁcant

energy to the target surface.

5.1.2. LIBS instrumentation

The experimental setup for LIBS used in this study is shown in Figure 56. The
laser in the LIBS is the KrF excimer laser (Lambda Physik®, model COMPex 301) with a
wavelength of 248 nm, a rectangular pulsed beam of l.3><3.0 cm2 in IBM mode, a
maximum pulse energy of 1.5 J and a maximum repetition rate of 10 Hz. The imaging
optics setup includes an automatic aperture unit, a set of planar convex lenses (focal
lengths 295 mm and 50 mm) and a focal point positioning unit. The focused spot size
used in the LIBS is 650 um in diameter. Three gas nozzles are installed around the
objective lens to deliver regulated dynamic gas-stream over the irradiation spot. The

nozzles are positioned about 3 mm from the irradiated spot and 30° degrees to the ﬁlm

surface.

110

 
  
 
 
 
  

BEAM ,

EXPAND“ AUTOMATI w ‘ , ._
APERTURE EXCIMER LASER Ho-Ne

GUIDING LAER

 

 
  

PLANAR
OBJEC11VE LENS CONVEX LENS

  
 

REGULATED GAS STREAM

 
 

_ FUSED SILICA
0 FIBER OPTICS

    

 

 

 

MONOCHROME‘I’ER cco oErEcron om meno-
MULn-cHANNEL °°NTR0LLER COMPUTER
cco DETECTOR
i l
PLANAR CONVEX I 5

FL: 295 mm Q

TO CCD
DETECTOR

 

   

 

 

Figure 56. Schematic diagram of the LIBS setup for the acquisition of the laser-induced
plasma on the CVD diamond ﬁlm.

The diameter of the gas nozzle is 2 mm, and the maximum gas ﬂow rate is 9.44x104
m3/sec. Helium and argon gases are used to dynamically alter the environment. Details
of the excimer laser, imaging optics and the gas-streaming unit are discussed in Chapter
3.

Emission spectra of the laser-induced plasma were collected by the fused silica

ﬁber optics, which has a range of wavelength transmittance from 240 nm to 2200 nm.

111

Both ends of the ﬁber optics were polished with a series of diamond suspensions in
particle sizes of 30 um, 6 um, and l um. The colloidal silica, average particle size of

0.06 pm, was used for the ﬁnal step of the polishing. To collect the emission spectra,
input end of ﬁber optics was installed at right angle to the incident laser beam, 5 mm
from the center of the irradiation. The distance, between the ﬁber optics and the center of
the laser irradiation, was kept to prevent deposition of ablation debris on the ﬁber optics,
which resulted in drastic decrease in signal intensity. The ﬁber optics geometry in the
system integrates spectral emission from the plasma, producing spatially averaged results
in the spectrum. The output end of the ﬁber optics was placed in the monochrometer,
Instrument SA, model HR—320. The monochrometer has the 0.32-meter coma corrected
Czemy-Tumer conﬁguration [82], which includes a 147 grooves/mm grating with a
reciprocal linear dispersion of 20.8 nm/mm. The primary function of the monochrometer
is to isolate the wavelength of interest from other wavelengths. The isolated emission
spectra were detected by a multi-channel CCD detector, EG&G PARC, model 1430P.
The solid state CCD detector is composed of a matrix array of 576 columns by 384
horizontal tracks of charge-coupled pixels. When the matrix is exposed to a spectral
source, photons strike the matrix generating electrical charge in the pixels. The charge in
each pixel is ampliﬁed for analog signals, and then the analog signals are converted to
14-bit digital format in the CCD detector controller, EG&G PARC, model 1430-1. The
digital signals are transferred to the OMA microcomputer, EG&G PARC, model 1460,
for the signal processing.

In the LIBS in this study, the scanning range of wavelength was set from 350 nm

to 825 nm. The intense reflection of the incident laser beam (248 nm) was screened by a

112

long-pass 350 nm optical ﬁlter. The resolution for the emission spectra, gained by the
combination of the monochrometer and the detector, was 0.47 nm. The exposure time
was set at 3 second, and the repetition rate of the excimer laser pulse was set at 10 Hz.
By the exposure time and the repetition rate, the time-integrated emission signals for 30
successive laser irradiations were accumulated for each measurement. Emission lines
from a mercury lamp [77], which show sharp and intense peaks in 200 nm to 600 nm
wavelength region, were used for wavelength calibration of the emission spectra. To
reduce the noise to the detector, all acquisitions of emission spectra were performed in a
darkroom condition. The dark current of the detector was measured separately for each
acquisition condition and subtracted for background correction of emission spectra.

A thick CVD diamond ﬁlm (ST235), average thickness 110 um and average grain
size 50 um, was used to allow enough ablation depth for the high-energy laser irradiation.
The silicon wafer substrate, where the CVD diamond ﬁlm was grown by the hetero-
epitaxial growth, was completely dissolved in the etching solution (50%I'IN03 + 25%HF
+ 25%CH3COOH) to acquire a freestanding diamond ﬁlm. The substrate side of the
freestanding diamond ﬁlm, which retained ﬂatness similar to the polished silicon wafer,
was exposed to the laser irradiation. The surface of the diamond ﬁlm was carefully
cleaned to prevent irrelevant spectra from organic contamination. To remove surface
contamination, the surface of the diamond ﬁlm was cleaned by ethanol in an ultrasonic
cleaner, and exposed to 5 laser pulses prior to the acquisition. Each acquisition was taken

on a fresh diamond surface for consistency.

113

5.1 .3. Identiﬁcation of line emission spectra

To examine the characteristics in emission spectra among the gas processing
environments, emphasis was placed on observation of broad wavelength range, from 350
nm to 825 nm. Identiﬁcation of the line emission spectra for the observed range was
performed by comparing the acquired LIBS results to various standard sources. The
standard atomic emission spectra from Notional Institute of Stand and Technology
(NIST) were used for the identiﬁcation of the line spectra from atoms and ions. The
NIST has developed a computer software, NIST Atomic Spectra Database (NIST
Standard Reference Database #78) [95]. This database can provide access and search
capabilities for critically evaluated data on atomic energy levels, wavelengths, and
transition probabilities. The molecular linear spectra were identiﬁed by tabulated
molecular standard spectra [96]. Related investigations for LIBS, carbon emission
spectra [68, 69, 89, 97—105], and ambient air breakdown [106, 107], were also referenced
to verify the identiﬁcation.

In Figure 57, the indexing maps display all probable atomic and molecular
emission spectra with the emission spectra by LIBS on the diamond ﬁlm. The line
graphs show the emission spectra of the diamond ﬁlm from the various gas processing
conditions, and the bar graphs at the bottom show the standard emission spectra for the
indexing. In the graphs, an arbitrary unit for the emission intensity was used for both the
LIBS results and the standard spectra. The diamond emission spectra were obtained from

the gas processing environments, such as ambient air, helium gas-stream and argon gas-

stream.

114

 

 

 

12000 ii
5 g A! “I'll“
. f g H. .I'..m
............... .mmgm at:
10000 -'

- c atomtc epectra
- N atomlc spectra
- 0 atomic spectra
3315132? Ar atomic spectra

 

 

 

 

 

 

 

 

 

 

 

8000 - _ He atomic spectra
Ar stream
0000 -
g Ha stream
E 4000 - a
. / ‘ bl nt alr
i,’ 1....” “i/ am 0
‘ .,,..,../"Mu..,.-~.,. I,.....v/«‘-“. .4
2000
350 400 450 500 550 600 050 700 750 000

wavelength (nm)

(b)

 

 

  

 

 

 

 

 

 

 

 

12000 g

3 ——Ar gee etream

.. g ---------- ~ He gee stream

1 .............. .mbhn‘ .I'
10000 T : - 0 molecular epectre

‘ g - N molecular epectra

“ l - 0 molecular epectra
8000 -
Ar stream
0000 -
... Ha stream '
g 4000 - ,. ‘5 ‘b ’H'” ‘ ' ‘ N
x’ ' 2 . r‘: am an a r
. . ; (:_ ~/ V‘
. . . ...’ " “’ i/ .
. \ﬂ".«"’\“‘~‘.‘u.-‘"~,..-.l“ ‘\--““’“v'h_,..why,“sn \_ ‘ “Jr—A
2000
. i ii i . _ .
' ‘ i l ' l l I l
o l 1 l e l' I I v I
350 400 450 500 550 000 050 700 750 000

wavelength (nm)

Figure S7. Indexing map for the emission spectra on the CVD diamond ﬁlm, a) indexing

map for the atomic emission spectra, b) indexing map for the molecular
spectra.

115

The laser irradiance was 6.0x108 W/cm2 for all conditions, and gas ﬂow rate was 5x10“1
m3/sec for the helium and argon gases. Figure 57a shows the indexing map for the
atomic emission spectra. For the atomic spectra from environmental gas breakdown, the
collected data were compared with neutral and singly ionized standard emission spectra
of oxygen, nitrogen, argon and helium. Higher levels of ionization of the environmental
gases do not show signiﬁcant contributions to the breakdown spectral emission [106,
107]. For the atomic emission spectra of the diamond, all ionization levels of the carbon
(CI ~ CV) were compared to the collected spectra from the irradiation. Indexing map for
the molecular emission spectra is shown in Figure 57b. All probable molecular emission
systems of carbon, oxygen, and nitrogen are compared with the LIBS results from the
various gas processing environments. Details of the molecular systems for the each

element and identiﬁcations of the corresponding emission spectra are discussed in the

following sections.

5.1.3-a. Identiﬁcation of carbon emission spectra

Identiﬁcation of carbon emission spectra is carried out by comparing collected
emission spectra with both the band systems of molecular carbon emission spectra and
individual emission spectra from carbon neutral and ions. In Figure 58, the emission
spectra from the various gas processing environments are compared with the molecular
carbon emission bands. The diatomic carbon emission bands and carbonitride emission
bands were considered for the identiﬁcation of the laser-induced plasma emission lines.

The names, transitions and occurrences of the molecular emission bands are listed in

Table 10.

116

 

 

 

 

 

 

 

 

 

.‘3 8000 -
C
3
g 6000 -
a ] . .
2 am blent air
3 4000 -
E .
U)
5 2000‘
.E .
O ' F ' I ' I ' F T I ﬁ I I I f I ﬂ I '
350 400 450 500 550 600 050 700 750 000
Q 8000 -
C
13 1
S 00001
E .
e * He gas streaming
59, 4000 ~
.E J
2
2 2000 -
.E .
0 I I ' I I I ' I ' I I I I I ' I I I
350 400 450 500 550 600 650 700 750 800
g 8000 -
c J
3
5‘ 6000 -1 .
g l Ar gas streaming
is, 4000 -
g 1
‘8 2000-
e
.E .
0 I I I n I I I I . I I I I I I I I I
350 400 450 500 550 600 650 700 750 800

wavelength (nm)

.1” i, it“ ,idp 0,ng .illll, lilii,

 

 

ll]

 

 

 

 

 

E . a

:3: C2 d’m’s system C2 Swan system

E

'5 W iuiL,1, llLli’Jlll p g
E TEN Violet system T CN Red system

1,1,Ll,i,l,,ll,,il,,, ,,1

02 High pressure system

Figure 58. Identiﬁcation of molecular carbon emission spectra from the LIBS on CVD
diamond ﬁlm.

117

Table 10. Molecular emission band systems for carbon and carbonitride [96, 100].

 

name of molecular

transition

 

 

 

 

 

 

occurrence
spectra
C2 Swan system A 3118 -) X 311., 0 direct excitation of C2 molecules
(ﬁI’St positive bands) 0 formation of excited state (d3IIg) C2 molecules
via dissociation or recombination
0 very frequent occurrence in sources containing
carbon.
C2 High Pressure A 3H: -) X 3H,, - condensed discharge through CO at relatively
system high pressure
C2 Deslandres- c 'II8 -) b ’11,, o condensed discharge through CO, CO2, or C2H2
d’Azambuia’s system
CN Violet system B 22‘. -) A 3II 0 carbon plasma in air
- discharge tubes containing nitrogen and carbon
CN Red system A 2n -> x 22 . introducing C2H2 and HCCl; into active nitrogen

 

 

0 carbon arc in air
0 discharge tubes containing nitrogen and carbon

 

As shown in Figure 58, the intense C2 Swan bands and CN Violet bands were

observed in the collected spectral emissions. Weak signals of the both C2 Deslandres-

d’Azambuja’s system and C2 High pressure system were identiﬁed as well. In contrast to

the strong CN bands, no signiﬁcant emissions for the CN red bands were identiﬁed.

Figure 59 shows the comparison of the dominant molecular emission, CN Violet bands

and C2 Swan bands, among the gas processing conditions. The plasma emission spectra

in ambient air exhibit very strong CN Violet bands and the lowest C2 Swan bands. In

contrast, the argon gas-streaming shows the strongest C2 Swan band emissions with

signiﬁcantly reduced CN Violet bands. The helium gas processing condition shows the

lowest CN Violet band emissions with higher C2 Swan bands than those of ambient air.

 

118

\CN Violet bands

C2 Swan bands

 

 

 

 

 

 

 

 

 

 

 

 

 

\

b ‘ I \\‘ K ‘ ~,
9). . Ar stream

He stream

 

 

°seasse
mtensnty (arbitrary unit)

  
  

 

ambient air

 

 

 

Figure 59. Comparison of dominant molecular emission bands, CN violet and C2 Swan,
among the gas processing conditions.

Figure 60 shows identiﬁcation of atomic carbon emission spectra from the laser-induced
plasma on the CVD diamond ﬁlm. Compared to the molecular spectra, relatively weak

emission signals of the neutral carbon (CI) and the singly ionized atom (CII) were

identiﬁed in Figure 60.

119

 

 

 

 

8000
I F

.E 1

3 6000 J

3‘ . .

S ambient aIr 3 8
g d v- N
E E K
3 4000 .4 $2 8 5 i u;
3‘ {I go; t4 :3 In,
- " .. 3 =2

I- ~ [x
g 0 0 = ... l:
g 2000 - l l T 0‘0
0 ﬂ l I I I T r [ I I j I I I I *l T I j
350 400 450 500 550 600 650 700 750 800
8000 -

A i 88
“E :53...

$6000 1 He gas streaming E2 77$

9 . e a 8.8.5
jg” w 06 = Ens}
V g; - 00::
g ct II! T ‘ T

U)

C.

22 2000 - T

.E

 

 

 

 

 

 

 

 

 

 

 

 

 

0 I l’ T l f I j I I l I I I I I I I l I
350 400 450 500 550 600 650 700 750 800
8000 1 88
FN
‘ a:
l I
. N3
6000 - Ar gas streaming g; 53,.-
e E:
-I ~ [\- he:
0 8 00
A 4000 - I =
.E O
3 . l
t W U
:2 2000 1
:2:
9 i
i!
.é‘ 0
m I ' I I ﬁ' I I l I I I 1 I 1 I l I I I
5 350 400 450 500 550 600 650 700 750 800
‘5

carbon atomic emission spectra

 

lvbltjl‘ l ' “IQ f 'l 1.1 '11" rlivl ll

1' , I. '1 ii
wavelength (nm)

Figure 60. Identiﬁcation of atomic carbon emission spectra from the LIBS on CVD
diamond ﬁlm.

v

120

Relative emission intensity, which is the ratio of a line spectrum to a continuum
background, is compared among the gas processing conditions. The neutral atomic
spectra of CI 447.18 nm, CI 538.03, and CI 711.32~711.98 nm exhibit no signiﬁcant
difference in relative intensity among the processing conditions. In contrast, the emission
spectra of singly ionized atoms, CII 657.81 and C11 711.56~712.20, show a signiﬁcant
increase in relative intensities in helium gas processing conditions. The helium gas

processing also developed additional singly ionized spectra at C1] 723.13~723.64 nm.

5.1 .3-b. Identiﬁcation of environmental gas breakdown

The emission characteristics of the laser-induced plasma are largely inﬂuenced by
the surrounding atmospheres. When the laser irradiance exceeds the energy threshold of
ionization potential, the high-energy electrons in the plasma induce the breakdown of
gases in surrounding atmospheres. To identify the environmental gas breakdown,
collected emission spectra were compared with both the molecular and atomic emission
spectra of the surrounding gas elements. Molecular and atomic spectral data of nitrogen,
oxygen, argon and helium [95, 96] are used for the identiﬁcation. The results were also
compared with other LIBS studies for ambient air breakdown [106, 107].

Figure 61 shows the identiﬁcation of molecular breakdown of nitrogen and
oxygen gases. In the all gas processing conditions, no prominent feature was identiﬁed in
both the molecular nitrogen and the molecular oxygen emission spectra. The lack of
molecular emission spectra indicates that the relaxation of excited nitrogen and oxygen
occurred by transitions of atomic energy levels, rather than transitions of neutral

molecules [107].

121

 

 

 

 

a“: ‘ F
E .
3
2‘ 6000-
,? ambient air
5 i
L.
3; 4000+
.3;
U)
8 m
g —i
0 I I I I I ' r I I T I I I 1 I j— I '
350 400 450 500 550 600 650 700 750 800
8000-

i

He gas streaming

intensity (arbitrary unit)
N A
% .§

 

 

 

 

 

 

 

 

 

 

 

0 I I I l ‘I I j I I T I 1 I I I ‘l I l
350 400 450 500 550 600 650 700 750 800
30001
.12 i
C
3 6000-
Z‘ .
<3 Ar gas streaming
'é 4000-
3
g 4
2 U
3 20004 M
.E
9 o I l I I T I r I I I I ' T I I I I l 1
5 350 400 450 500 550 600 650 700 750 800
2‘ wavelength (nm)
g
i l Illllll l
3 “HUM”, - . . 'Jll . Vlrrllil‘
2‘ . .
g N2 emussron spectra (nm)
2
.E

 

 

 

 

lllll , v , i -ll l, l

02 emission spectra (nm)

I

Figure 61. Identiﬁcation of molecular environmental-gas breakdown from the LIBS on
CVD diamond ﬁlm

122

The laser-induced breakdown of ambient air produces free electrons and ionized nitrogen
and oxygen atoms. The recombination of the free electrons and the ionized atoms
generates atomic line spectra as the excited electrons relax to the ground states. Then, the
atomic nitrogen and oxygen combine to form molecular nitrogen and oxygen. However,
the atomic recombination does not have sufﬁcient internal energy to generate molecular
line spectra in the observed wavelength range [107]. In LIBS in this study, the atomic
emission route of nitrogen and oxygen is supported by the absence of molecular emission
spectra and the presence of atomic emission spectra.

Figure 62 shows the identiﬁcation of atomic gas breakdown for the nitrogen,
oxygen, helium and argon. In the ambient air, relatively weak signals of 01 777.19 ~
777.54 nm and NI 404.13 ~ 404.35 nm are identiﬁed. In the argon gas steaming
condition, the well-known intense argon neutral emission spectra are shown in the range
between Arl 696.53 nm ~ ArI 811.54 nm. The atomic nitrogen spectra are also shown at
NI 567.60 nm ~ 568.62 nm, NII 592.78 nm ~ 595.24 mm and NI] 642.06 nm ~ 643.77
nm. In the helium gas steaming condition, no indication of helium gas breakdown was
observed. The identiﬁed atomic spectra of nitrogen and oxygen are signiﬁcantly reduced
in the helium gas-streaming condition. Only traces of the weak atomic oxygen spectra
(01 777.19 ~ 777.54 nm) and the weak atomic nitrogen spectra (567.60 ~ 643.77 nm)

were found near the continuum background.

By combining the atomic and molecular spectra, Figure 63 and Figure 64 list the

all identiﬁed emission spectra found in LIBS on the CVD diamond ﬁlm.

Figure 62. Identiﬁcation of atomic environmental-gas breakdown from the LIBS on

 

123

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

He atomic spectra

CVD diamond ﬁlm

1

ll

53 8000-
C
3 4 Ln . o
2‘ m. ambientair 3
g 6000- § ,.-
.. l:
e . «i» .2
£3 40004 § "-
a . _ E
"’ 5
g 20004 T 1
.E .
o l ' I ' I If 1 T T ' I i I V I ' I ﬁ
350 400 450 500 550 600 650 700 750 800
900001
C
:3 l
a. c
g 6000‘ He gas streaming
g
b—
59,4000-
E
2
2 2000.
.E
o ' T I I ' I I I ' I V T I l 1 ﬁ
350 400 450 500 550 600 650 700 7%) 800
A - N I l: .
‘E 8000 .q g g 3 8 t; 3
= . Ar gas streaming § 3; , 8; ,7; 8g
Z‘60004 ' i3 8 are ~‘5 " 3-
9 § § N 82 r 3 2‘?
’5 3 s on 2 <
3 4000- ? i 5'5
s . i
2 2000- U
,9.
.E
0 t I ' ﬂ? T ﬁ l ' I T I f ﬂ r l
350 400 450 500 550 600 650 700 750 800
wavelength (nm)
E i ,llllnl MW ,1 Lilli”; l, [ILL , , 1L i Ii
5 nitrogen atomic sptecra
E
h
g. '1 I 1'1 til 1 f 1111111] 14' [II I 1' 1”
g l I I T l’
,2 oxygen atomic sptecra

 

 

will

Ar atomic spectra

124

 

vwdmm I ohmmm =2 hmdmm cmkw a

         

Nwdmm I owﬁom ~Z

N

  
   

  

  

 

 

   
   
  

 

a mmdmm :95 m
. a mmdmm 526 a
NO me C63” 0 mw.omm Cﬂgm 0 u m m
00.53 cmgm 0 ﬂ S
8.33 .o e
N AN mNmINF mNm—z U
Nméwm 53m 0
8.3m 525 N0 a
hhdom .526 0a m a
. 2:32 _
8 8m ; .x o 8.0% .. 8.8.. _
mm. E 5.5 No .32 53w No SN? 5
oudov I mvdov 53m NO
913 66S 20 2.8“. $.05 20 I I.

 

mmdmv «22> 20

8.8“. - $3.. $5 N

o. Fm». «22> 20
and; 8.2) 20 0...me “22> ZO

 

3.va I vmﬁwv 5.05 20

irradiance at 6.0X10'° chm2

 

vmdmm I momma «22> ZO

vodmm I mmdmm «22> ZQ

 

8.2.. .. 5.8.. massage No A

mméov I 9.33

ambient air

    

 

 

8000

. T . 1 . . I a 4 a . _
as. 5:53 £225

 

600

550

500

450

400

350

wavelength (nm)

Figure 63. Identiﬁed line emission spectra by LIBS on the CVD diamond ﬁlm in the

wavelength region 350 nm ~ 600 nm.

125

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

. l. m M .m
”3.5 .2 m m t
. I V .m m
av Pow ~.<. “V N
No was 95 N m m
mime .2 $E-2E_DHHW
U
[”585 3. iv
8.8a .2
llU
2 8.»? _
m 2
W 8.8» .. 9.85 :0 F.
0 8a: .. emcﬁwmwomauﬁ .. m3: 5 - I.»
10 U
1 3.80 E
X
0 N
6 I
w. 2.. n8 85 o l
e 6. So no &
m
.m Page - 8&5 :z llr
d .
m N w
i ~36 29.6 III
a ads $5 a
s 3. m8 85 o r
a me. So 83m 0
I a. 8?. on. «8 :2 3. 8m :95
~38 .. 8.3m .2 .I
3.8..“ 55 No madam Saw a
I 8.33 cm;
a d I q 4 [q d d u -‘ d — d —
now 0 0 0 m 0 0 O
o m m m m m m
8 7 6 5 4 2 1
9:: $593 $825

 

600 650 700 750 800
wavelength (nm)

wavelength region 550 nm ~ 825 nm.

550
Figure 64. Identiﬁed line emission spectra by LIBS on the CVD diamond ﬁlm in the

126

5.1.4. Influence of laser irradiances on emission spectra

To observe the inﬂuence of laser irradiances on the emission spectra, the diamond
ﬁlm was subjected to various laser irradiances from 2.4x108 W/cm2 to 8.4x108 W/cmz,
with an increment of 1.2x108 W/cmz. The gas processing environments were ambient

air, helium gas-stream and argon gas-stream. The gas ﬂow rate was constant at 5><10'4
m3/sec for the helium and argon gases. Carbon molecular emissions are observed in
lower intensities than those for the carbon atomic and ionic emissions. The molecular
carbon bands have been well observed in the laser irradiance over 106 W/cm2 [68, 69, 74,
93, 100, 108]. The carbon atomic and ionic emissions require that the laser irradiance
reach 108 W/cm2 [69, 100]. Due to the high laser irradiance range (2.4x108 W/cm2 to
8.4x108 W/cmz) of this study, the carbon molecular emission spectra were observed in all
laser irradiation levels. The carbon atomic and ionic emission spectra were weak at the
low laser irradiances near 2.4x108 W/cmz, but were becoming prominent toward the
higher laser irradiances near 8.4xlO8 W/cmz.

Figure 65 shows the intensities of plasma emission spectra in the ambient air. As
the laser irradiance increased, both the background and the line spectra were increased.
In the ambient air, the strong CN Violet bands are dominant in all irradiance levels. The
C2 Swan bands appear at the lowest laser irradiances, and the intensity of the bands are
increased with the laser irradiance. In contrast to the molecular emissions, the atomic

emission spectra were not prominent at the low laser irradiances.

127

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LASER IRRADIANCE
CN Violte bands C2 Swan bands 1: 8.4x10' Wicm’
‘ ’ o 2
2: 7.2x10 chm
3: 6.0x10' MM2
1 4: 4.0x10' chm’
5: 3.6x10' chm'
a: 2.4x10' Warn” 3
g E.
I a 93.
a
a 0 E
g o
a
a
:2
e
3
E
2
a
.s 1

 

 

 

 

 

    

 

A

5

iii

K,
3‘1:

i.

l”

 

I I T I I I I I
450 500 550 600 650 700 750 800

wavelength (nm)

 

Figure 65. Laser—induced plasma emission spectra on the diamond ﬁlm in ambient air as
a function of the laser irradiance.

128

As indicated by CH 657.81 mm and OI 777.19 ~ 777.54 nm, the atomic spectral
intensities at 2.4x108 W/cm2 are hardly recognized in the continuum background. As the
laser irradiance increased, the atomic spectra were becoming prominent. This tendency
was also observed in CH 657.81 nm in argon gas-streaming in Figure 66. The inﬂuence
of the laser irradiance on CN Violet bands and C2 Swan bands in argon gas-streaming
was analogous to that on the molecular bands in the ambient air. The breakdown of
argon gas was clearly observed by the intense singly-ionized argon (ArI) peaks in all
laser irradiance levels. Even though helium gas-streaming in Figure 67 exhibited
relatively low molecular emission spectra, the dependence of the spectral intensity on the
laser irradiance on was similar to the other gas processing conditions. The helium gas-
streaming exhibited the most intensive carbon ion emission spectra among the gas
processing conditions. The CH 657.81 nm in Figure 67 showed relatively high emission
intensities even at the lowest laser irradiance. The singly ionized oxygen, OI 777.19 ~
777.54 nm, in helium gas processing condition showed the evolution of emission
intensity similar to that of the ambient air.

The relationship between spectral intensity and laser irradiation are important to
analyze properties of the laser-induced plasma. From Figure 68 to Figure 70, dependence
of emission intensities on laser irradiance is shown among the gas processing conditions.
The emission spectra and continuum background, as well as the ratio between those, are
plotted as a function of the laser irradiances. A representative spectrum was chosen for

each of the major molecular and atomic emission systems.

129

 

LASER IRRADIANCE
: 8.4x10' Wicm’
: 7.2x1o' WIcm’
6.0x1o' Wicm’
: 4.8x10' chmz
: 3.6x1o' Wicm’
2.4x10' Wlem2

12000 -

C2 Swan bands

 

V

10000-

11
QObQN-ﬁ

 

 

 

8000-

 

gN Violte bgds

 

 

CI! 657.81

 

 

 

 

 

 

intensity (arbitrary unit)

 

 

 

 

 

3
V4 l ‘ .
t5, 'WM

I I I I I 7
350 400 450 500 550 600 650 700 750 800

wavelength (nm)

 

 

 

Figure 66. Laser-induced plasma emission spectra on the diamond ﬁlm in argon gas-
streaming as a function of the laser irradiance.

130

 

 

 

  
   

 

 

 
  

 

700° LASER IRRADIANCE'
‘ 1: 0.4::10' Mom”
02 Swan bands _ E 2: 7.2x10‘ Mon”
6000 _ ‘ E 3: 6.0x10' Mama
0 4: 4.0x10' WIcm’
. 5: 3.6::10' Men”
6: 2.4x10‘ chm’
5000 -
ﬁg
3 1000 ' 3
5 CN Violte bands E
E i '
O)
:m- E
.5. a
.5
2000 -

 

6.

I r I I I T l I I 7
350 400 450 500 550 600 650 700 750 800

wavelength (nm)

Figure 67. Laser-induced plasma emission spectra on the diamond ﬁlm in helium gas-
streaming as a function of the laser irradiance.

intensity (arbitrary unit)

(a) G Swan bands in ambient

131

air

 

C2 Swan band: 516.52 nm
continuum background

A

 

 

ratio (spectrum/background)

 

 

r

é 5: S 3
laser irradiance (X103 W/cmz)

30000 (b) CN Violet bands in ambient air

 

 

 

 

 

 

 

‘ - CN Violet band: 388.34 nm A
A 25000‘ a continuum background tc’
’§ ‘ <3
3 200004 _ g.
g . (0
E 15000- g
3 1 a
E 10000« g
2 o.
0 ‘ 3;
E 5000- .9
. 2:?
M
c I A A U A! j + I
2 4 6 8
laser irradiance (x1o° W/cmz)
(C) CH 657.81 nm in ambient air
1 - Cll atomic spectrum: 657.81 nm
2500- . continuum background ’2‘
:3; ‘ E
2‘ 2000. g:
g ' as
:8 1500- E
3 ‘ 2
E 1000- g
2 o.
' (D
2 v
.5 500- .9
l E
o W

 

 

 

7 S 0
laser irradiance (X108 W/cmz)

 

 

 

 

5 (a-1)
4.
3.
2..
1
1 . S - S f
2 4 6 8

304

25-

20<

15:

laser irradiance (X10° W/cmz)

(b-1)

 

 

 

 

 

a 0
laser irradiance (X108 W/cmz)

(0'1)

 

1.64

d

1.5-

J

1.4-

1.3:

 

1.2

 

 

v

T

4

V

5 C3 8

laser irradiance (x108 W/cmz)

Figure 68. In the ambient air, the intensities of the emission spectra and the continuum
background are plotted as a function of the laser irradiance, a) C2 Swan band,
b) CN Violet band, and C) CH. Corresponding ratios of the emission spectra
to the background are shown in, a—l) C2 Swan band, b-l) CN Violet band, and
c-l) C11. The guide lines are arbitrarily drawn to show trends of the data.

132

(a) C. Swan bands in He streaming (3'1)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R
- C2 Swan band: 516.52 nm
6000‘ . continuum background (a
A C
’E": 3 4.
3 B:
x
g i a 3"
a o-o
'g 2000« é
o 3
E . g 2.
0 I ' ' ' I ' I I ' I v r r r
2 4 6 8 2 4 6 8
laser irradiance (X10a W/cmz) laser irradiance (X108 W/cmz)
(b) CN Violet bands in He streaming (b-1)
- CN Violet band: 388.34 nm
a continuum back round A 2
,2 3000- g g 2'5
S g .
5 '1‘:
;_= 2000- “'
g g 2.07
.5: s
g 1000‘ g
g E 1.5:
‘6
0 I I I f I ' I I I I ‘— ‘r ' I
2 4 6 a g 2 . 4 6 8 9
laser irradiance (X10 W/cm ) laser Irradlance (X10 W/cm )
(c) CH 657.81 nm in He streamlng (c-1)
5000. - CII atomic spectrum: 657.81 nm
1 . continuum background :5 1-6‘ . .
7.3 5000« S '
‘3: i 9
a 4000- .32 1.5-
:! . a
g 3000 g r
" : 1.4-
% 2000- g
5 - a
g 1000‘ .g 1 3‘
. g '
0 ﬂ ‘ I f I ' I r v I v r . 1
2 4 6 a 2 4 6 8
laser irradiance (X10a W/cmz) laser irradiance (X10“ W/cmz)

Figure 69. In the helium gas-streaming, the intensities of the emission spectra and the
continuum background are plotted as a function of the laser irradiance, a) C2
Swan band, b) CN Violet band, and c) CH. Corresponding ratios of the
emission spectra to the background are shown in, a-l) C2 Swan band, b-l) CN
Violet band, and c-l) C11. The guide lines are arbitrarily drawn to show
trends of the data.

133

 

 

(a)C. Swan bands in Ar streaming 1 (a-1)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0
‘ - 02 Swan band: 516.52 nm 9‘
10000 ‘ continuum background :3 1
7.3 ‘ g 8«
C a .
3 8000 5: 7.
E‘ J {a .
,g 6000 m 6:
S ‘ E 5-
2 a :
2 2000‘ ‘ 1’.” 3~ o
.E A .0 ‘
1 E 2. .
0: 1 1
2 4 6 8 2 4 6 e 2
laser irradiance (X10° W/cmz) laser irradiance (X10 W/cm )
(b)CN Violet bands in Ar streaming (b-1)
- CN Violet band: 388.34 nm 5.0.
7500. . continuum background :5 .
c g 4.5“
g 9 ‘
Z‘ 3’ 4.01
g 5000~ 8 ,
_._. 3.5:
g 2500‘ g 3.0-]
5 3” 2.5-
,g 1 .9 .
0‘ : S 2.02
2 ' 4 ' é ' £3 2 ' 11 f 6 ' 0
laser irradiance (X10° W/cmz) laser irradiance (X10° W/cmz)

(c)CII 657.81 nm in Ar streaming 1 (c-1)

 

 

   

 

 

 

 

 

 

C
7000. - CI] atomic Spectrum: 657.81 nm_ '
i ‘ continuum background A °
... 6000i 2 1.4-
.‘.'.' 3 o
S 5000- g
a: . 6 1.32
(I!
,3 4000: S
E ‘ E ‘
3 3000: a 1.2-
.? 1 E
g 20004 3
m V 2
.2: 1000} .2 1'1
‘ ‘3
0‘ I f I ' I f I 1.0 I ' I V T ﬁ' l
2 4 6 8 2 4 6 8
laser irradiance (X10° W/cmz) laser irradiance (X10° W/cmz)

Figure 70. In the argon gas-streaming, the intensities of the emission spectra and the
continuum background are plotted as a function of the laser irradiance, a) C2
Swan band, b) CN Violet band, and c) CH. Corresponding ratios of the
emission spectra to the background are shown in, a-l) C2 Swan band, b-l) CN
Violet band, and c-l) CH. The guide lines are arbitrarily drawn to show
trends of the data.

134

The C2 Swan bands at 516.52 nm, CN Violet bands at 388.34 nm and carbon atomic
emission at CH 657.81 run were selected for the comparison among the gas processing
conditions. For the continuum backgrounds, the nearest continuum level of the each
representative spectrum was used.

In Figure 68, the emission intensities in ambient air are shown as a function of
laser irradiance. The guide lines are arbitrarily drawn to show trends in the data. In
Figure 68a~c, all of the emission spectra and continuum background exhibit increases in
their intensities as the laser irradiance increases. The largest gap between emission
spectrum and continuum background in Figure 680 illustrates the most intensive emission
of CN Violet bands in the ambient air. In the lowest laser irradiance, the singly ionized
carbon spectrum at 657.81 nm in Figure 680 shows the smallest spectral intensity
difference between the spectrum and the continuum background. The spectral intensity
of CH 657.81 nm drastically increased with an increase in the laser irradiance, which
substantiates the active ionization of carbon atoms in higher laser irradiances. In the C2
Swan bands (Figure 68a-1) and CN Violet bands (Figure 68b-1), the ratios of the
emission spectrum to the continuum background were decreased as the laser irradiance
increased. This indicates the substantial increase in continuum background emission in
high laser irradiance, as compared to the molecular emission spectra. In contrast, the
ratio of CI] 657 .81 nm to continuum background was increased with an increase in the
laser irradiance. The increasing ratio indicates the active ionization of carbon atoms in
higher energy laser irradiance region.

In Figure 69, the emission intensities as a function of laser irradiance are shown

for the helium gas-streaming condition. Similar trends were observed for all of the

135

emission spectra and continuum background, and they exhibit increases in their
intensities as the laser irradiance increases. The spectral intensity of CH 657.81 nm also
showed drastic increases with an increase in laser irradiance. Consistent with the
observation in ambient air, the molecular emission bands, C2 Swan (Figure 69a-1) and
CN Violet (Figure 69b-1), exhibited the decrease in ratios of the emission spectrum to the
continuum background. The increase in the ratio of CH 657.81 nm in Figure 69c-l was
observed as well.

The relationship for the argon gas-streaming condition is shown in Figure 70 that
the trends were analogues to the observations in ambient air and helium gas-streaming.
In Figure 70a~c, the increase in laser irradiance resulted in an increase in emission
spectra for both the line spectra and continuum backgrounds. The C2 Swan bands in
Figure 70a exhibited the most intense spectral emission, as compared to the their
continuum background. The smallest difference of the spectral intensity was found
between the singly ionized carbon emission (Figure 700) and its continuum background.
The behavior of the spectrum to the background ratios was consistent that the descending
trend was found in the molecular emission spectra (Figure 70a-1 and b-l). The ascending
trend of the ratio was also found in the atomic carbon emission (Figure 700-1).

Regardless of the gas processing environments, the measured intensities of the
emission spectra and continuum backgrounds behaved as an exponential function of laser
irradiance. The behavior of the spectral intensity, which is proportional to the

concentration of the molecular and atomic species, can be modeled by the exponential

function:

 

I(r)=Io-ea[ '0) Equation20

136

where I(r) is a spectral intensity (arbitrary unit) at laser irradiance r, la is spectral
intensity at the detection threshold, a is an irradiance coefﬁcient, r is a laser irradiance
(W/cmz), and r0 is a laser irradiance at the detection threshold. The irradiance coefﬁcient
a is an empirical constant, which depends on energy levels of the spectrum and
environmental factors of the laser irradiation. The irradiance coefﬁcient can be obtained
by boundary conditions of the measured intensities. Figure 71 shows the agreements
between the measured emission intensities and the proposed relationship in Equation 20.
The emission intensities of C2 Swan band at 516.52 nm, CN Violet band at 388.34 nm,
and CH 567.81 nm were subjected to the equation, which modeled exponential
relationship between the emission intensity and the laser irradiance. In all gas processing
conditions, the measured emission intensities in the scattered points showed good
agreement to the modeled exponential functions in the curved lines. The irradiance
coefﬁcient a, displayed in the Figure 71, were obtained from Equation 20 by inserting

lower and upper boundary values of the spectral intensity and the laser irradiance.

5.1.5. Excitation temperature of the laser-induced plasma

The temperature of the laser-induced plasma is one of the most important
applications of quantitative LIBS. Measuring temperature of an excitation source helps
to understand the dissociation, atomization, ionization and excitation processes [68-70,
74, 78, 82, 83, 85, 86, 89-91, 97, 100, 108-111]. The excitation temperature of the

plasma can be deduced by an assumption that the plasma is in local thermodynamic

equilibrium (LTE).

137

(a) C2 Swan band: 516.52 nm

 

 
  
  
 

- ambient air: a=0.731
i a He stream: a=0.644
- Arstream: a=0.434

  

intensity (arbitrary unit
é

 

 

 

f v j ﬁr

4 6
laser irradiance (X10a W/cmz)

Nd
(”-1

(b) CN Violet band: 388.34 nm
0000

 

 

 

 

.ﬁ'é‘ 25000‘ - ambient air: a=0.661
3 y a He stream: a=0.825 '
E 200004 - Ar stream: a=0.792
E .
3 15000‘ .
'2‘ 4
17, 10000“ I
c 4
(D
g 5000~
0 ‘ . . .

 

Nd
A
0:
co

laser irradiance (X108 W/cmz)

(0)611: 567.81 nm

- ambient air: a=0.898
i 2 He stream: a=1.014
5000‘ . Ar stream: a=1.081

 

7500

intensity (arbitrary unit)

 

 

 

 

f ﬁ f I If I v U v I r

a 3 4 5 6 7 a ' 9
laser irradiance (X108 W/cmz)

Figure 71. Modeling of the emission intensity of the CVD diamond as a function of the
laser irradiance for the various gas processing conditions; a) C2 Swan band at
516.52 mm, b) CN Violet band at 388.34 nm, and C) CH 567.81 nm. The
displayed values of irradiance coefﬁcient a were obtained by lower and upper
boundary values of the emission intensities and laser irradiances.

138

The plasma in LTE follows the Boltzmann distribution of electronic states of atoms and
molecules for a given temperature in a localized area. The excitation temperature is
calculated by emission intensity ratios from different upper energy levels of an element in

the same electronic state.

Using the vibrational quantum number v, the transition from an upper molecular
vibrational level v’to an lower molecular vibrational level v”is denoted by (vf v”). The
intensity of spectral emission, resulted from the transition (vf v”), can be related to the

initial state molecular population [108]:

I”. = KN VAW.(%C-) Equation 21
where 1.2» is the intensity of a spectral emission from the transition of molecular
vibration level v ’to v’C K is proportionality constant (cm3-sec/J) related to the sensitivity
of the acquisition, N, is the number population (cm'3), AW is Einstein transition
probability of spontaneous emission (sec'l), h is the Plank constant (6.63x10'34 J see), c is
the speed of spectral emission (tn/sec), and 11 is wavelength (nm) of the spectral emission.

According the wave mechanics in radiation, the Einstein transition probability is related

to the electron transition moment [108]:

 

647!4 -- 2 E ' 22
.. = va quatlon

where R”, is the transition moment. Then the intensity of spectral emission can be

written as:

Equation 23

1.... = [64”401‘ (R E(ﬁj

3 h 114

139

The terms, c, K and R”, are not variables in the equation. Substitute the constant terms

for C; and rewrite the equation for the relationship among va, N,, and ,1:

N .
Iv'v" = Cl [77) Equation 24

When the plasma is in LTE, the number population N, is given by the Maxwell-

Boltzmann equation[85, 86, 108]:

EV
NV = N0 .e *7 Equation 25
where N, is the total number population (cm'3) , E. is energy state at the molecular
vibrational level v, k is the Boltzmann constant (1.38><10'23 JIK), and T is the excitation

temperature (K). The vibrational energy E, can be obtained by the relationship to the

term value 0., [108]:

 

Gv = E, = a)(v+-1—) Equation 26
he 2

where a) is the measured vibrational frequency in cm], and the v is the vibrational

quantum number. Combining Equation 24, Equation 25 and Equation 26, rearranging

and taking natural logarithm give the equation:

1110141,...) = ln( Cl N 0 ) — (E- %v Equation 27

140

Finally, the equation for the excitation temperature can be expressed by considering
various molecular vibration energy levels, and substituting the constant term for C [69,

70, 74, 108]:

in Z (141W) = C - (%}i(v) Equation 28

In Equation 27, a plot of ln(/14Iv2~) in various vibrational levels as a function of G(v), at a
constant temperature T, yields a linear relation with a slope equal to — (he/kT) and a
interception C. The excitation temperature T can be calculated from the slope of the plot.

For the spectroscopic measurements the temperature of the molecular excitation,
distinctive emission peaks in various vibrational energy levels are required. In this study,
the C2 Swan bands appeared prominent in all of the gas processing conditions and all of
the irradiance levels. The emission spectra of the C2 Swan bands in various vibrational
transition levels, 516.52 nm (0,0), 512.93 mm (1,1) and 509.77 nm (2,2) were chosen to
deduce the excitation temperature. The locations of the emission spectra are indicated in
Figure 72.

For the plot of ln(/14Ivv) as a function of G(v) in Equation 28, the emission
intensities 1w” were measured from the Figure 65, Figure 66 and Figure 67. G(v) is
obtained by Equation 26 with tabulated a)[108]. Figure 73 shows the plots for ln(/t"lw~)
as a function of G(v) in various laser irradiances in the gas processing conditions. The
linearity of the data was assumed, and the slopes of the linear lines were calculated. The

calculated values of the slopes were displayed in Figure 73.

.1.
.5
.a

1000

 

750 1

c2 Swan 512 93 (1 1)
*0, Swan 516.52 (0.0)

C, Swan 509.77 (2.2)

500 -

 

intensity (arbitrary unit)

250 -

 

ambient air at 2.4 chm2

 

 

l l I I I

I I
430 490 500 510 520 530 540 550
wavelength (nm)

Figure 72. Emission spectra of the C2 Swan bands in various vibrational transition levels
used for the temperature measurements.

Figure 74 shows the excitation temperature of the C2 Swan bands in various gas
processing conditions as a function of laser irradiance. The deviation ranges displayed by
the error bars resulted from the regression range of the linear ﬁt for the data in Figure 73.
The deviation range observed in this study was 6% ~ 25%. Typical accuracy ranges were
reported about 80% ~ 95% in spectroscopic temperature measurements [74]. The
uncertainty of this temperature measurement depends on the existence of the assumed
LTE, the accuracy of the instrumentation and the error range of spectroscopic constants

of the molecular emission lines.

142

(a) ambient air
‘ 8.4x10' W/cm2

 

, _ -s
7.2X108 W/cm2 lope. 3.712X10

\\slope: -4.259x10'5
w I
slope: «1.641x10'5

4.8x10' W/cmz

ln(

slope: -4.820x10"

 

 

1 \\ slope: -5.4|94x10'5
25 01 2.4x10’ W/cm’ slope: -6.184x10'5
0 1000 2000 3000 4900 5000 6000
G(v) cm

(b) helium gas streaminL

 

slope: -4.3p7x10‘5
slope: -5.288x10"

slope: -5.795x10’5

slope: -6.1;llx10'5
lope: -7.705x10"

In(
N N
sn 9»
9-9.

slope: -8.565x10"

 

 

0 fldoo'zdoorsﬁ'mﬁsdoojsobo

 

 

 

.1
G(v) cm
(C) argo_n_gas streamlnl
28.0. \\
slope: 45.30010s
A 27.6- .5
f» slope: -7.569x10
N3
V A .
i: and slope: -7.876x105
E .5
a slope: -9.433x10
26.82 . 4
slope: -1.002x10
sl :-1.183x10"
26.4 °P° .

 

0 f1000'2000‘3000'4000'5000'60100
G(v)cm'1
Figure 73. ln().4lvw) in various vibrational levels as a function of G(v) in various laser
irradiances in the gas processing conditions, a) ambient air, b) helium gas
processing, and c) argon gas processing.

143

 

 

 

 

50000

“000‘ 0 ambient air
A He stream

40000 2 I Ar stream

 

temperature (K)

 

 

50‘” I ' I ' I ' I ﬂ I ' I - I '
2 3 4 5 6 7 8 9

laser irradiance (X10“ W/cmz)

 

 

Figure 74. Excitation temperature of the C2 Swan bands in various gas processing
conditions as a function of laser irradiance.

The temperatures measured in Figure 74 are deduced from time-integrated
intensities, which provide average temperature values for the molecular excitation. In all
gas processing conditions, the excitation temperature was increased as the laser irradiance
increased. The rate of increase in temperature appeared to be approximately constant for
all of the gas processing conditions. The plasma in ambient air showed the highest
excitation temperatures in the given irradiance range. The excitation temperature reached
to 3.9x104 (K) at the laser irradiance 8.4X108 W/cm2 in the ambient air. In contrast, the

excitation temperature in the argon gas-streaming showed the lowest proﬁle in the

144

irradiance range. The temperatures observed in the argon gas-streaming were about 45%,
in average, lower than those in the ambient air. In the helium gas-streaming, the

excitation temperatures were about 25% lower than those in the ambient air.

5.1.6. Electron density of the laser-induced plasma

In plasma, the emitting atoms or ions are under the influence of electric ﬁelds,
which are produced by relatively rapidly moving electrons and slowly moving atoms and
ions. The pressure broadening of a line spectrum is caused by perturbations of the
electric ﬁeld by collision of the charged particles that contains a permanent dipole
moment [85, 86]. Because the electric ﬁled is involved, it is called the Stark broadening.
By studying the well-known hydrogen lines, the Stark broadening was found out to be
proportional to the density of the charged species [85]. From the linear Stark effect, the
broadening of a line spectrum is proportional to the two-thirds power of the ion density,
which is equal to the electron density. The relation assumes that only the ﬁrst ionization
is important and the second ionization equilibrium is not important. The proportionality

between the line broadening and electron density is expressed by:

n, = C(n, ,T)A/t3’2 Equation 29

where n, is the electron density (cm'3), C(ne, T) is a coefﬁcient that is only a weak
function of electron density and temperature, and A11 is full Stark broadening width. The
Stark broadening was compensated by considering two extreme broadening mechanisms,
quasi-static approximation and impact approximation [85, 86]. The quasi-static
approximation is valid when the particles move relatively slowly, so that the perturbation

is practically constant over the time. The perturbation is described by the order of the

145

inverse of the line broadening width. In contrast, the impact approximation assumes
unperturbation of the emitting systems, and describes the line broadening by the impact
theory of quantum mechanics [86]. According to the approximations, the compensations
was made on the coefﬁcient C(ne, T) with parameters of the electron impact and ion-
broadening. A practical equation for the spectroscopic measurement of the electron

density is suggested by [68, 85, 86, 90]:

. 1

l
n n 4 n -6-
M = 2 ‘16 1+ 4.75 :6 1— 0.068 4 Equation 30
10 10 T J

 

 

where a) is electron-impact half width (nm), n, electron number density (cm‘3), a is ion-

broadening parameter, and T is the temperature (K). The parameter a is obtained by
correlation between the peak broadening and the electric ﬁeld strength of singly charged
ions [85].

In this study, the carbon neutral spectral emission line (CI) at 477.18 nm (see
Figure 63 for the peak identiﬁcation) was measured for the Stark broadening width M
using full width half maximum (FWHM) of the peak. The FWHM of CI 477.18 nm was
measured in all gas processing conditions for comparison. The Stark broadening were

measured in higher irradiance levels of 6.0, 7.2 and 8.4x108 W/cmz, which exhibited

distinctive peaks at CI 477.18 nm. The measured M values are in Table 11.

146

Table 11. Measured FWHM values for the M (nm) in various gas processing conditions
and laser irradiances (W/cmz).

 

 

 

 

 

6. 0x108 W/cm2 7.2x108 W/cm2 8. 4x108 W/cm2
ambient air 3.94 nm 4.51 nm 4.84 nm
helium gas-streaming 2.50 nm 2.68 nm 2.91 nm
argon gas-streaming 2.11 nm 2.51 nm 2.79 nm

 

 

 

 

 

The measured M are inserted in Equation 30 for the electron density calculations. The
values of the electron-impact half width (0 and the ion-broadening parameter aare well

tabulated in references [85, 86] for the carbon atomic emission spectra. The a) and a
values for the CI 477.81 nm spectrum were 0.0157 nm and 0.043, respectively [86].
Since Equation 30 is the weak function of the temperature, a rough estimation of the
temperature can be assumed for the calculation [68, 85, 86, 112]. This assumption was
veriﬁed in this study that the variation in temperature rage of 105 resulted in less than
0.1% of the variation in the calculated density. The estimated value of 2000 K was used
for the calculation [68].

Figure 75 shows the calculated electron densities in various gas processing
conditions as a function of the laser irradiance. The electron densities in Figure 75 are
calculated from time-integrated intensity of the emission spectrum, which provide
average electron density values of the laser-induced plasma. In the given range of the
laser irradiance, all gas processing conditions exhibited an increase in the electron
densities as the laser irradiance increased. The densest population of electrons was found

in the density proﬁle of the ambient air.

147

 

 

 

 

 

 

 

+ ambient air
1'6 '- —A— He stream
‘ —I— Ar stream
«5‘
E 1.4 -
o
'2
x
V 1.2 -
5‘
a)
c
e“
c 1.0 "
9 /
8 //A//'
m 0.8 - /
0.6 ' T l’ 7

 

' I I ' I ' I
6.0 6.5 7.0 7.5 8.0 8.5

laser irradiance (x10° W/cmz)

Figure 75. Electron density in various gas processing conditions as a function of the laser
irradiance.

The electron density in ambient air reached to 1.6x1018 cm’3 at the laser irradiance

8.4)(108 W/cmz. The argon gas-streaming showed the lowest density proﬁle among the
processing conditions. The helium gas-streaming showed slightly higher density proﬁle
than that of argon gas—streaming, but signiﬁcant differences were also found as compared
to the density proﬁle in the ambient air.

There are a few sources that cause uncertainty of the calculated electron densities
[85, 86]. The instrumentation, which requires precise measurement of FWHM of the line
spectrum, is one source of errors. In the case of weak or very broad lines, it is difﬁcult to
not only determine the underlying continuum background but also differentiate the

contributions from other line spectra. The calculated Stark broadening parameters also

148

contain up to 10% of uncertainties. Errors can be caused when substantial amount of
self-absorption occurs and when electron density changes in the acquired spectra. The
Doppler broadening, which is caused by kinetic temperature of emitted atoms and ions,
can be the most important competing broadening mechanism. However, the Doppler
broadening is negligible in LIBS, which involves dense laser-induced plasma with neutral
or singly ionized emission spectra [68, 74, 84-86, 90]. All these possible sources of
uncertainty reduce the reliability of the absolute value of the calculated electron densities.
However, the relative value among the calculated electron densities, in which the
emission spectra are acquired in the same instrumentation, have reasonably high
reliability from the proved nature of the Stark broadening. The reliability of the relative
value gives strong credibility on the comparison of measured electron densities among

the gas processing conditions in this study.

5.1.7. Physical and chemical interpretation of the emission spectra

In this LIBS study on the CVD diamond ﬁlm, the most active carbon emission
systems were C2 Swan bands, CN Violet bands and atomic CI and C11 spectra. The
atomic CI and C11 spectra appeared distinctive in higher irradiance range (> ~ 4x108
W/cmz). The breakdown of environmental gases was also observed by atomic emission
spectra of nitrogen, oxygen and argon. The molecular emission spectra, C2 Swan bands
and CN Violet bands, were prominent throughout the entire irradiance range (2.4x108
W/cm2 to 8.4x108 W/cmz) in this study. The physical and chemical interpretation of the

molecular emission bands leads this study to the better understanding on the laser-

induced plasmas on the CVD diamond ﬁlm.

149

5.1 .7-g. C2 Swan bands

The C2 Swan bands appeared in emission spectra of all gas processing conditions.
The C2 Swan bands resulted from relaxation of excited C2 molecules. The argon gas-
strearning showed the most intensive emission spectra of the Swan bands, while the
ambient air showed the lowest intensities. High electron density of laser-induced plasma,
with increased population of charged particles, stimulates the emission for the Swan
bands. The origins of the Swan bands have been suggested from other spectroscopic
investigations on carbon species [68, 69, 89, 100].

When the laser-induced plasma expands to the ambient after the termination of
the laser pulse, the high-energy electrons in the plasma start to lose their energy. Then,
the excited states of molecules, atoms and ions are created by heavy-body collisions, ion-
electron/ion-ion recombination, and electron-molecule dissociative recombination [113].
Heavy-body collisions of metastable atoms and metastable molecules, called Penning
collision, is considered as a weak but possible mechanism for producing the Swan bands
through excited C2 molecules. The presence of Penning collision tends to increase the
continuum background [100]. The ratios of the emission spectra to the continuum
background were observed in Figure 68, Figure 69 and Figure 70 for the Swan bands.
The consistent decrease in the ratios as a function of the laser irradiance indicates the
relative increase in the continuum background to the emission spectra. The increase in
the continuum background is the plausible indication of the presence the Penning
collision. However, the contribution of Penning collision to the excitation of C2

molecules are negligibly small as compared to other strong mechanisms [100].

150

One of the electron-ion recombination processes is a two-body collision between

an electron and a C2 cation:

e' + C; _, C; Equation 31

where the ‘*’ indicates the excited stage. This appears to be the most direct and plausible
mechanism to create excited C2 molecule, but other investigations [100, 114] have shown
that it is unlikely due to the rapid energy loss of colliding electrons. The electrons in
expanding plasma lose their energy rapidly into ambient, which reduces their energy far
less than ~ 3 eV for the recombination [114]. The other electron-ion mechanism is a
three-body collision among an electron, a C2 cation and a neutral inert gas atom. In this

study, helium and argon were used for dynamic streaming gases, which result in the

three-body processes:
e’+C;+He—)C;+He Equaﬁon32
e’ +C2++Ar—)C;+Ar Equation 33

The third body, the neutral inert gas atom, assists the process by transporting its excessive
energy to the colliding electron. The electron gains energy from the third-body collision
partner to form the excited C2 molecule [97, 100]. The energy to create an excited argon
atom is much lower than that to create an excited helium atom. For example, the ﬁrst
ionization energy of argon is 15.76 eV and that for helium is 24.59 eV [95]. Hence, the
three-body process with argon is expected to be more likely than that with helium. This
speculation is supported by the LIBS in this study in which the C2 Swan bands were
much more intensive in argon gas-streaming than in helium gas-streaming (see Figure

59). Accordingly, the ambient air without the inert collision partner showed the lowest

151

intensity of the Swan bands. The strong plausibility of Equation 33 is furthermore
supported by the abundance of the intense argon neutral atomic spectra in this study (see

Figure 64). The abundance of excited argon neutral atoms leads to another plausible

mechanism by charge exchange:

C; + Ar’ -> C; +Ar“ Equation 34

This charge exchange between an excited argon atom and a carbon cation strengthens the
intense Swan bands in the argon gas-streaming in this study. Similar to the case
discussed in the three-body process, the high ionization potential of helium makes the
generation of Swan bands via the charge exchange unlikely in the helium gas processing
condition.

The C2 Swan bands can be produced by ion-ion recombination in which carbon

cation and anion are recombined to form excited C2 molecule:

C + C‘ __) C; Equation 35

The atomic cation and anion recombination is regarded as a plausible mechanism for
laser irradiance over 108 W/cm2 due to the increase in population of ionic particles at the
high laser irradiance regime [114]. In this study, the plasma was induced by the laser
irradiance levels over 108 W/cmz. The atomic CI and C11 spectra appeared distinctive in
irradiance range over ~ 4x108 W/cm2 (see Figure 63 through Figure 67). This is a good
indication of increased population of carbon ionic reactants in the laser-induced plasma.
However, the population of the atomic anions in the laser-induced plasma is expected to
be orders of magnitude smaller than that of the atomic cations and electrons [7, 115].

Accordingly, the probability of the recombination between the carbon cations and anions

152

is much more smaller than that of the recombination between the carbon cations and
electrons. Thus, the carbon cation and anion recombination is a weak but plausible
mechanism for the production of the Swan bands in high laser irradiance regime.

The most plausible mechanisms for spectral emission of the Swan bands is the
electron recombination with C,. cations (n > 2) and metastable C,. molecules (n > 2),

which results in dissociation of excited C2 molecules:

e‘ + C; —> C,,_2 + C,‘ Equation 36

e‘ + C; —> C;_, + C; Equation 37

This mechanism is called dissociative recombination where the excited C2 molecules are
relaxed to the ground state emitting the C2 Swan bands. As n increases in the Cu clusters,
the conditions for dissociative recombination become more likely. This is due to the
increase in internal degrees of freedom, in which electrons can be coupled to dissociate
the excited C2 molecules. Several investigations on laser-induced plasmas [68, 89, 98,
99, 111] have shown the abundance of the carbon clusters, which are formed by both the
multiphoton fragmentation upon the laser irradiation; and the nucleation from carbon
vapor consisting of carbon atoms and small carbon molecules. The carbon clusters in
laser-induced plasma showed copious distribution of small clusters (n < 30) and larger
clusters, as large as n > 400. These carbon clusters increase the number of pathway by
which the dissociative recombination in Equation 36 and Equation 37 can take place.
The statistically high chances of the reactions make the dissociative recombination
process the most plausible. Early investigations on carbon emission spectra [100, 113,

114] found evidences for the presence of two distinctive velocity distributions of the bulk

153

emissions. The signiﬁcant attribution of dissociative recombination was conﬁrmed in the
recent investigation [98] by measuring the time-of-flight emission spectra on a graphite
target. In the investigation, the faster velocity components were explained by emissions
generated from the recombination processes, and the slower components were attributed

to dissociative recombination of the carbon clusters resulting in the generation of C2
molecule.
5.1 .7-b. CN Violet bald;

The CN Violet bands can be produced by ion-ion combination in which carbon

and nitrogen ions are collided to form excited CN diatomic molecule:

C"+N‘—>CN' Equation38
C'+N+ —)CN' Equation 39

The nitrogen cations are assumed to be abundant from the observation of the nitrogen gas
breakdown in all laser irradiance levels in this study. Increased population of the carbon
atomic cations are also observed in laser irradiance over ~ 4x108 W/cmz. However, the
population of the atomic anions is expected to be orders of magnitude smaller than that of
the atomic cations and electrons [7, 115]. Hence, the probability of the recombination
between cations and electrons is much more higher than that of the combination between
cations and anions. The relatively small population of anion reactants makes the ion-ion
combination a weak mechanism for the CN Violet bands.

According to the speculations discussed in the dissociative recombination for the
C2 Swan bands, the abundance of the carbon clusters in the laser-induced plasma supports

a plausible pathway for the CN Violet bands:

154

C; + N‘ —> C,,_l + CN' ““360“ 4"
c; + N ’ —> CL, + CN ' Equation 41

The proposed reactions involve the generation of excited gaseous CN by dissociative
combination between a carbon cluster (n > 2) and an excited neutral nitrogen atom. The
neutral nitrogen atom is activated in the laser-induced plasma, and collides to the
metastable carbon cluster and the cation carbon cluster, as shown in Equation 40 and
Equation 41, respectively. In this study, the dissociative combination is also supported
by observation of the breakdown of nitrogen gas (see Figure 62 ~ Figure 64), which
generates sufﬁcient amount of reactive nitrogen atoms. The CN Violet bands by the
dissociative combination are the most intensive spectral emissions in the ambient air in
this study (see Figure 63 ~ Figure 65). Thus, it can be assumed that the abundance of
nitrogen in ambient air transformed the laser-induced carbon clusters into gaseous CN
molecules. In this speculation, substantial amount of laser-ablated carbon species has to
be vaporized by the reaction in Equation 40 and Equation 41. The observation on
ablation debris supports the signiﬁcant vaporization of carbon cluster in the ambient air.
Figure 76 shows the ablation debris deposited around the irradiation spots among
the gas processing conditions. In Figure 76a, the laser irradiation in ambient air resulted
in a signiﬁcant decrease in ablation debris, as compared to Figure 76b and c in other gas
processing conditions. The magniﬁed views of the near spot area in Figure 76a-1, b-l and
c-l also prove that the ambient air in Figure 76a-l shows signiﬁcantly decreased debris

deposition, as compared to the helium gas-streaming in Figure 76b-l and the argon gas

streaming in Figure 76c-1.

155

 

 

20 um 5 um

 

 

 

Figure 76. Comparison of ablation debris around the irradiation spots among the gas
processing conditions; (a) and (a-l) ambient air, (b) and (b-l) helium gas-
strearning, and (c) and (c-l) argon gas-streaming.

156

Thus, it is conclusive that the laser-irradiation in ambient air, in which the CN Violet
bands are the major emission spectra, resulted in signiﬁcant formation of gaseous
carbonitride molecules. Other gas processing conditions, in which the major emission
spectra was the C2 Swan bands, showed larger amounts of debris deposition. The argon
gas steaming in Figure 760 shows the largest amount of deposited debris due to the
breakdown of the argon gas. As discussed in the mechanisms for the Swan bands, the
breakdown of argon gas results in the abundance of electrons, and excited argon neutrals
and ions, which promoted the formation of C2 molecules by the additional mechanisms,
such as the electron-ion interaction (Equation 33) and the charge exchange (Equation 34).
As compared to the argon gas-streaming, relatively small amount of ablation debris were
found in the helium gas-streaming, in which the plausible mechanism was only the

dissociative recombination in Equation 36 and Equation 37.

157

5.2. Images of Laser-Induced Plasma

5.2.1. Interaction of laser-induced plasma

An incident pulsed laser beam interacts with a target material in phototherrnal and
photochemical processes [23, 38, 78]. In the phototherrnal process, the absorption of
photons leads to the excitation of electrons, which consequently transfers the energy in
the form of heat to the lattice. Melting and evaporation occur, and the high-temperature
plasma is induced from the energy transfer. In photochemical process, the absorbed
photon energy is dissipated through breaking of chemical bonds, which results in
instantaneous evaporation, called the ablation.

Figure 77 shows the schematic diagram for the interaction of the laser-induced
plasma to its surrounding. The high-temperature plasma interacts with the surrounding in
two ways. Firstly, the expansion of the high-pressure plasma drives shock waves into the
surrounding, and secondly, energy is transferred to the surrounding by a combination of
thermal conduction, radiative transfer, and heating by the shock waves [23, 27, 78].
Even though the laser-material interaction is limited to nanoseconds to femtoseconds
ranges for most of the pulsed lasers, the plasma extends far longer than the laser pulse

duration [27, 71, 116]. The duration of the plasma has been observed in tens of

microseconds.

158

 

LASER IHRADIA‘I'ION
SHOCKWAVTNT
HEAT RADIATION
HEAT
CONVECTION
RADIATIVE HEAT

TRANSFER /

    

_’
SURFACE HEAT CONDUCTION
/ / i l \

THERMAL CONDUCTION

TARGET MATERIAL

Figure 77. Interaction of laser-induced plasma to the surrounding [23, 27, 78].

The evolution of the plasma depends on laser irradiance, composition of a target martial,
laser wavelength, and ambient gas composition and pressure.

The expanding plasma can transfer signiﬁcant amount of energy to the target
surface by thermal conduction, and radiation. The plasma-material interaction gives rise
to changes, such as surface phase transformation, material ejection and re-deposition, and
spoiled interfaces. Observation of the plasma, by image capturing, is valuable to

characterize details of the expansion of the plasma.

159

5.2.2. Image capturing of laser-induced plasma

The experimental setup for the image capturing is shown in Figure 78. The
plasma was induced on a CVD diamond ﬁlm (ST235), which has an average thickness of
110 um and average grain size of 50 um. The laser in the setup is the KrF excimer laser
(Lambda Physik®, model COMPex 301) with a wavelength of 248 nm, a rectangular
pulsed beam of 1.3x3.0 cm2 in TEMoo mode, a maximum pulse energy of 1.5 J and a
maximum repetition rate of 10 Hz. The focused spot size used for the image capturing is
650 um in diameter. The spot size was produced by the imaging optics, which includes
an automatic aperture unit, and a set of planar convex lenses (focal lengths 295 mm and
50 mm). Three gas nozzles are installed around the objective lens to deliver regulated
dynamic gas—stream over the irradiation spot. The nozzles are positioned about 3 mm
from the irradiated spot, and 30° degrees to the ﬁlm surface.

A charge coupled device (CCD) camera was used to capture the time integrated
images of the laser-induced plasma. The CCD camera used for the capturing was
Javelin®, model Chromachip II, equipped with a convex objective lens in 27 mm focal
length. The CCD camera was positioned at 20° angle to the target surface. The image
capturing was synchronized with the pulsed laser irradiation at 10 Hz repetition rate, and
7.5x108 W/cm2 laser irradiance. The captured signals are transferred to the video image
board, Matrox® Marvel 6200, for digital image processing. The CCD camera and the
video board were set to 100 us acquisition time frame for the synchronization to the laser

pulse repetition rate of 10 Hz.

160

AUTOMATIC '
APERTURE EXCIMER LASER

    
  
   

 

PLANAR
ﬂ CONVEX LENS

  

 

REGULATEI) GAS sr

/
"4

i cco CAMERA.

CENTRAL COMPUTER

OPTICAL FILTER

 

 

IMAGE CAPTURING
& PROCESSING UNIT

 

PLANAR CONVEX
FL: 27 mm
OPTICAL FILTERS
BP400 or LP525

 

 

 

 

Figure 78. Schematic diagram for the time—integrated image capturing of laser-induced
plasma on the CVD diamond ﬁlm.

Optical ﬁlters, band pass 400 nm (BP400), and long pass 525 nm (LP525), were placed to
screen the intense reﬂection from the laser beam, and to illuminate the extent of the

expanding plasma. The wavelength pass ranges of the optical ﬁlters are shown in Figure

79.

161

 

 

 

 

 

 

 

 

 

 

 

(a) Band pass ﬁlter: BP400 nm
50
50
a .0
3
a II
g; 30
e
3
20
a
C
0
g 10
o ' /—"/
200 300 L 400 500 000 700 900 900
wavelength (nm)
(0) Long pass filter: LP525
100 -
A m '-
? i
3
E ”i
'e
3 4o .
E:
a, .
5
o l-
200.300.400‘500‘600‘TOOIBOO‘900

wavelength (nm)

Figure 79. Plots showing wavelength pass ranges for the optical ﬁlters; a) band pass
ﬁlter BP400, and b) long pass ﬁlter LP525.

162

5.2.3. Time-integrated images of laser-induced plasma

5.2.3-a. Laser induced plasma on CVD diamond

Figure 80 shows an example of the synchronized capturing of the time-integrated
images of plasma. The series of images were taken from the argon gas-streaming without
the optical ﬁlter. Each image was obtained by 100 us time-integrated acquisition, from a
single pulse of the laser irradiation at 25 ns. Among the series of acquired images,
representative sets of the plasma images are shown in Figure 81 for the ambient air,
Figure 82 for the helium gas steaming, and Figure 83 for the argon gas-streaming. From
the time-integrated plasma images, the extent of the laser-induced plasma is compared.

Figure 81 shows the plasma images captured in the ambient air. Unﬁltered image
in Figure 81a shows not only the image of the laser-induced plasma, but also the intense
reﬂection of the incident excimer laser. The intense reﬂection of the laser beam is
ﬁltered by a BP400 ﬁlter in Figure 81b. The brightest region at the center of the
irradiation spot indicates the most intense irradiation near the wavelength of 400 nm.
The extent of expanding plasma over wavelength 525 nm is shown in Figure 810, ﬁltered
by the LP525 ﬁlter. The lowest longitudinal expansion of the plasma was observed in the
ambient air. In contrast, the lateral expansion of the plasma is relatively strong. The
lateral expansion is prominent in Figure 81c, in which the ejection of large particles

(indicated by the arrow) was frequently observed.

163

Diamond (Ar gas-stream, no filter) :

III
II“

 

   

 

Figure 80. Example of the synchronized capturing (100 us time frame acquisition for the
10 Hz irradiation) of the time-integrated plasma images. Each image is
captured by 100 us integrated-acquisition from a single pulse of the laser
irradiation.

164

no ﬁlter .354: Luv

8 P .100 531;. [3 .l l I 1‘

05".“ till“

 

Figure 81. Time-integrated image of laser-induced plasma on the CVD diamond ﬁlm in
ambient air; a) unﬁltered image, b) image captured with BP400 ﬁlter, and c)
image captured with LP525 ﬁlter, the arrow indicates the ejection of a large
particle.

165

The images of the plasma for the helium gas processing are shown Figure 82. An
unﬁltered image, in Figure 82a, shows a more spherical-type of expansion than that for
the other gas processing conditions. In Figure 82b, the lateral expansion is signiﬁcantly
reduced as compared to the ambient air. In contrast, the longitudinal expansion is more
prominent than that in the ambient air. Figure 82c, with the LP525 ﬁlter, consistently
shows the prominent expansion in the direction normal to the target surface. At the room

temperature (~ 293 K), the density of helium (0.1664X10‘3 g/cm3) is lower by one order
of magnitude than that of argon (1.663x10'3 g/cm3), and the difference between argon

and air (1.275x10'3 g/cm3) is relatively small [117]. The low density of helium, which
creates lowest conﬁnement among the processing environments, could explain the
spherical expansion of the plasma. The particles in expanding plasma can travel further
in the environment with low density. The spherical symmetry resulted from the increased
degree of freedom in the radial expansion. The breakdown of environmental gases had
an insigniﬁcant contribution to the emission spectra in the helium gas-streaming. The
breakdown of helium was not observed, and the breakdown of nitrogen and oxygen was
minimized.

Figure 83 shows the images of the laser-induced plasma in the argon gas
processing condition. The largest extent in both the lateral and longitudinal directions
was observed in the unﬁltered image in Figure 83a. Figure 83b shows the largest bright
region in the center of the irradiation spot, which indicates the most intense irradiation

near the wavelength 400 nm region, among the gas processing conditions.

166

no ﬁl ter Eli-Lit m-

8 P400 ‘53 Li Ill 1 ‘

65‘:- lm‘

 

Figure 82. Time-integrated image of laser-induced plasma on the CVD diamond ﬁlm in
the helium gas-streaming; a) unﬁltered image, b) image captured with BP400
ﬁlter, and c) image captured with LP525 ﬁlter.

167

no ﬁlter ct": w

Bl’x‘tC 0 b5 ".i' I" 1‘

Lit-L? tn 1 ‘

 

Figure 83. Time-integrated image of laser-induced plasma on the CVD diamond ﬁlm in
the helium gas-streaming; a) unﬁltered image, b) image captured with BP400
ﬁlter, and c) image captured with LP525 ﬁlter.

168

As shown in Figure 83c, the extent of expanding plasma, over wavelength 525 nm, is the
largest as well. The extensive plasma formation is mainly due to the breakdown of argon
gas in the laser-induced plasma. The breakdown of argon results in the well—known
intense argon emission spectra in the wavelength range between 700 nm ~ 1000 nm [77,
95]. As discussed in Section 5.1.6, the abundance of excited electrons, and ions from the
gas breakdown also assists the C2 Swan band emissions, which were the most intense
among the gas processing conditions (see Figure 63 and Figure 64).

The environmental gas breakdown was observed not only in the argon but also in
nitrogen and oxygen in ambient air (see Figure 63 and Figure 64). Even though the
breakdown threshold is nearly the same between the argon and the air, the largest plasma
was observed in the argon gas-streaming condition. Furthermore, the ambient air
exhibited the smallest extent of plasma among the gas processing conditions. The largest
extent of the plasma in the argon gas-streaming is mainly due to the very intense spectral
emissions from argon and the C2 Swan bands (see Section 5.1.7). The carbonitride
formation (see Section 5.1.7) in the ambient air is mainly responsible for the smallest
plasma formation. The atomic spectral intensity of argon gas was observed to be about 5
~ 20 times larger than that for the nitrogen and oxygen. The ambient air showed the
major emission spectra in the CN Violet bands, which consumed excited nitrogen
particles and active carbon particles. The vigorous carbonitride formation, which caused
the intense CN Violet band emission (385.09 nm ~ 388.34 nm) in the near-UV range,
drastically reduced the chances for other mechanisms in the visible emissions. In the
ambient air, both the C2 Swan bands and the continuum background are the lowest

among the gas processing conditions.

169

5,2.3-b. Effects of dynamic gas-stregming on plagma-materialinteraction

To examine the effects of dynamic gas-streaming on plasma-material interaction,
time-integrated images of laser-induced plasma were captured from the irradiation on the
therrnosetting polyester resin. The polymer target has low ablation threshold (~ 0.5
J/cmz), which is about ten times smaller than that of CVD diamond. The lower ablation
threshold of polymer materials results in the higher volume-ablation rate (cm3/pulse),
which gives large amount of ablated particles to form plasma. The laser irradiation on
the polyester resin causes instant fragmentation of polymeric hydrocarbon (CH2) chains,
creating large plume over the irradiation spot [118]. The large plume is useful for
observation of plasma dynamics in relation to the target surface. The same experimental
setup and irradiation conditions, described in Section 5.2.2, were used for the time-
integrated image capturing of laser-induced plasma on the polyester resin.

Figure 84 shows the time-integrated images of laser-induced plasma on the
polyester resin. To observe the extent and dynamics of expanding plasma, no optical
ﬁlter was used in all of the captured images. The plasma image in the ambient air is
shown in Figure 84a, which reveals the convection stream of plasma near the target
surface, as indicated by the arrows. The lateral expansion, which results in the
convection stream, is prominent in all of the captured images in the ambient air. Figure
84b shows the captured image in the argon gas-streaming condition. The extent of
plasma expansion in the argon gas-streaming is about the same as that in the ambient air.
However, the convection stream was not observed in the argon gas-streaming condition.
The dynamic gas-streaming of argon inﬂuenced the expansion dynamics of the laser-

induced plasma, and deterred the convection stream of plasma near the target surface.

170

ambient err 650 H m

Ar stream ' (350 um

He stream 650 IllTl

 

Figure 84. Time-integrated images of laser-induced plasma on the polyester resin; a)
image captured in ambient air, arrows indicate the convection stream of
plasma near the target surface, b) image captured in argon gas-streaming, and
c) image captured in helium gas-streaming, no optical ﬁlter was used for all
captured images.

171

 

 

 

 

 

 

 

ambient air 750 W" Ar stream 750 1"" He stream 750 um

 

 

 

 

 

 

 

Figure 85. Laser irradiation on a leuco-dye coated paper for thermal detection around the
irradiation spot; a) irradiation in the ambient air, indicating the temperature
increase around the irradiation spot, b) irradiation in argon gas-streaming, and
c) irradiation in helium gas-streaming.

The captured image of plasma in the helium gas-streaming condition is shown Figure
84c. The captured image in the helium gas-streaming shows the same signiﬁcantly
reduced extent of plasma, as compared to other gas processing conditions. Especially,
the lateral expansion is drastically reduced as compared to the ambient air.

The interaction, between the convection steam of plasma and the target, is
examined by the laser irradiation on the leuco-dye coated paper. A leuco-dye is an
organic dye, which is colorless by chemical treatment, but it restores its color by
oxidation. The oxidation is usually provided by exposure of leuco—dye molecules to air.
For a thermal detector, the leuco-dye molecules are sealed in phenol-type coating. When
the phenol-type coating is melted by a heat source, the leuco-dye is oxidized to restore its
color, indicating its exposure to the heat.

High-density leuco-dye coated paper from Trumpf Laser is used to detect the

interaction between the plasma and the target. The detection threshold of the leuco-dye

172

coated paper is about 100 °C. The diameter of focused laser spot was 500 um, and a
single pulse irradiation at 3.6x108 W/cm2 was used for the irradiation.

Figure 85 shows the laser irradiation on a leuco-dye coated paper for thermal
detection around the irradiation spot. In the ambient air (Figure 85a), the temperature
increase around the irradiation spot is detected by the colorization of the leuco-dye. In
contrast, the irradiation with dynamic gas-streaming conditions (Figure 85b and e) do not
exhibit the colorization. No obvious difference was found in the leuco—dye detection
between argon gas-streaming and helium gas-streaming. In connection to the observation
in Figure 84a, it is convincing that the convection stream of plasma near the target
surface causes the temperature increase around the irradiation spot. Likewise, the
dynamic gas-streaming reduces the plasma-target interaction by inﬂuencing the
expansion dynamics of the laser-induced plasma. The convection stream of plasma near
the target is deterred by the dynamic gas-streaming, as indicated by both the plasma

image capturing and leuco-dye detection.

173

5.3. Chapter Summary

In this chapter, laser-induced plasma on the CVD diamond ﬁlm was investigated
by analytic instrumentations, such as laser-induced breakdown spectroscopy, and time-
integrated plasma image capturing. The characteristics in emission spectra, among the
gas processing environments, were examined by the LIBS observations. The plasma
emission spectra in the ambient air exhibited very strong CN Violet bands and the lowest
C2 Swan bands. In contrast, the argon gas-streaming shows the strongest C2 Swan band
emissions with signiﬁcantly reduced CN Violet bands. The helium gas processing
condition shows the lowest CN Violet band emissions with higher C2 Swan bands than
those of ambient air. As compared to the molecular spectra, relatively weak emission
signals of the neutral carbon, and the singly ionized atom were identiﬁed. In the
observations on environmental gas breakdown, the atomic emission route of nitrogen and
oxygen is supported by the absence of molecular emission spectra, and the presence of
atomic emission spectra. The breakdown of argon gas was observed by the intense argon
neutral emission spectra, but no indication of helium gas breakdown was observed. The
mechanisms for the major spectral emissions are discussed, and most plausible
mechanisms are proposed in this study. The C2 Swan bands were appeared in emission
spectra of all gas processing condition. The C2 Swan bands resulted from relaxation of
excited C2 molecules. The dissociative recombination process of carbon clusters is
proposed for the most responsible mechanism for the C2 Swan bands. The argon gas-
strearning showed the most intensive emission spectra of the Swan bands, while the

ambient air showed the lowest intensities. The abundance of excited electrons, and ions

174

from the gas breakdown assists the C2 Swan band emissions. The three—body process,
and the charge exchange process are proposed for the additional sources for the intense
Swan bands in the argon gas-streaming. The mechanism of the strong CN Violet bands
in the ambient air is proposed by invoking the dissociative combination. The proposed
reaction involves the generation of excited gaseous CN by dissociative combination
between carbon clusters and excited neutral nitrogen atoms. The abundance of nitrogen
gas, in ambient air, transformed the laser-induced carbon clusters into gaseous CN
molecules, which reduced the substantial amount of laser-ablated carbon deposition
around the irradiation spot. The behavior of emission spectra is observed as a function of
the laser irradiance. Regardless of the gas processing environments, the measured
intensities of the emission spectra, and the continuum backgrounds behaved as an
exponential function of laser irradiance. The behavior of the spectral intensity is modeled
by the exponential function. In the molecular emission bands, the ratios of the emission
spectrum to the continuum background were decreased as the laser irradiance increased.
This indicates the substantial increase, in continuum background emission, in high laser
irradiance as compared to the molecular emission spectra. In contrast, the ratio of atomic
carbon emission spectrum to the continuum background was increased with an increase
in the laser irradiance. The increasing ratio indicates the active ionization of carbon
atoms in higher energy laser irradiance region. The excitation temperatures of the plasma
are deduced by the Boltzmann-plot method in which LTE of the plasma was assumed.
The plasma in LTE follows the Boltzmann distribution of electronic states of atoms and
molecules. The excitation temperatures are calculated by emission intensity ratios from

different upper energy levels of an element in the same electronic state. The plasma in

175

ambient air showed the highest excitation temperature proﬁle, while the argon gas-
streaming showed the lowest proﬁle. Electron densities are calculated from the
proportionality between the Stark effect on the line broadening and the electron
population. The calculated electron densities in various gas processing conditions are
presented as a function of the laser irradiance. In the given range of the laser irradiance,
all gas processing conditions exhibited an increase in the electron densities as the laser
irradiance increased. The densest population of electrons was found in the density proﬁle
of the ambient air. The argon gas-streaming showed the lowest density proﬁle among the
processing conditions.

Time-integrated images, in the ambient air showed the lowest longitudinal
expansion of the plasma. In contrast, the lateral expansion of the plasma is relatively
strong. The lateral expansion is prominent in ambient air, which showed the hottest and
densest plasma among the gas processing conditions. The plasma images for the helium
gas processing showed more spherical-type expansion than that for the other gas
processing conditions. The low density of helium, which creates lowest conﬁnement
among the processing environments, could explain the spherical expansion of the plasma.
The largest extent of the plasma, in both the lateral and longitudinal directions, was
observed in the argon gas-streaming. The largest extent of the plasma in the argon gas-
strearning is mainly due to the very intense spectral emissions from argon and the C2
Swan bands. The carbonitride formation in the ambient air is mainly responsible for the

smallest plasma formation.

Chapter VI

FABRICATION OF MICRO-COMPONENTS ON CVD DIAMOND FILMS

6.1. Maskless Patterning on CVD Diamond Films

For ultra-hard ﬁlm materials, such as CVD diamond, conventional machining and
lithography-based patterning are difﬁcult due to the high wear resistance and the
chemical inertness [3, 4, 41]. Nevertheless, superior material properties of the diamond
bring about their increasing use in various engineering applications, such as
semiconductor devices, sensors and microelectromechanical systems (MEMS) [16, 18,
20, 22, 23]. Furthermore, continuous developments in growth technologies, for larger
areas and low production costs, accelerate demands for diamond-based applications.
Patterning and micromachining of the diamond ﬁlm is a primary requirement to properly
modify a ﬁlm surface for the applications. Lithography-pattemed diamond growth has
been practiced for this purpose [54-57]. In the process, a lithography-pattemed
photoresist layer, in which diamond seeds are embedded, is placed in CVD reactor for the
diamond growth. Besides its step-intensive procedure, the process exhibits lateral growth
of diamond ﬁlm, which limits the resolution and aspect ratio of a patterned structure.

Pulsed laser ablation has proven for vaporizing ﬁlm materials to make patterned
structures and micro-components. The laser ablation is a direct process that requires only
proper arrangement of optics to control the laser beam. The CVD diamond ﬁlms have
been processed by various types of pulsed lasers, which have shown their capabilities in

polishing, etching, and patterning [14, 16-18, 20-23, 119]. However, the patterning and

176

177

micromachining of the ﬁlm were limited due the lack of versatility of the process. The
accuracy of the process was limited by the plasma-induced damage as well. In this study,
for solutions to these problems, the maskless patterning system was invented with the
dynamic gas streaming on the irradiation. The effects of the dynamic gas streaming were
discussed in Chapter 4 and 5. The innovative maskless patterning technique employs
pulsed irradiation of focused laser beam on a target material, which is translated to the
programmed positions by the micro-CNC. Along with its advantages of a simple setup
and a direct process, the maskless process makes a rapid prototyping possible for patterns

on ultra-hard ﬁlm materials [120, 121].

6.1.1. Maskless patterning versus lithography-based patterning

The comparison between the processing steps of the maskless ablation technique
and the lithography-based technique is shown in Figure 86. The maskless ablation
technique utilizes a stationary laser beam on a translating target material. The stationary
laser spot is formed by an aperture and two convex lenses. The size of the laser spot is
determined by the diameter of the aperture and the demagniﬁcation ratio of the optics.
The translation of the micro-CN C stage can be programmed by a computer for any
complex movements. Details about the maskless patterning system are discussed in
Chapter 3. The direct ablation on the translating target can rapidly create a pattern on the
diamond ﬁlm, as shown in Figure 86a. In contrast, as shown in Figure 86b, the
lithography-based patterning on the diamond ﬁlm requires the lithography with a

patterned mask on the diamond seeded photoresist layer.

178

I SI SUBSTRATE

 

. DIAMOND SEEDED
PHOTORESIST LAYER

   
  

 

uv LITHOGRAPHY

   
  

FULLY GROWN

 

DIAMOND FILM ON
"3W2. Sl SUBSTRATE
ETCH'NG
I
PATTERNED DIAMOND
3" ABLAT'O" PATTERNED DIAMOND
GROWTH IN seeoeo AREA

(a) LASER ABLATION TECHNIQUE (b) LITHOGRAPHY-BASED PATTERNING

Figure 86. Comparison of the processing steps between; a) the maskless ablation
technique, and b) the lithography-based patterning

The lithography is followed by the selective etching for the designed pattern.
Then, the diamond-seeded pattern is placed in the CVD reactor for the selective diamond
growth on the patterned area. The lithography-based patterning is not only a step-
intensive process but also a low-resolution process. The diamond growth on the
diamond-seeded pattern proceeds to not only longitudinal directions but also lateral
directions. The excessive lateral growth spoils the resolution of the pattern, which is
important for the patterning of integrated features on the diamond ﬁlm. Figure 87 shows
the lithography-based patterned sensor (thermistor), grown from the diamond-seeded
photoresist layer. As illustrated in Figure 87d, the lateral growth on the edge of the
pattern is prominent in Figure 87b and c.

The CVD diamond ﬁlm has great potential for the sensors, such as pressure

sensors, therrnistors and photodetectors.

179

      
 

d LONGITUDINAL encmm
LATERAL snow ——-9 LATERAL GROWTH
srucou suesmre mmouo seeoeo,

PATTERNED PHOTORESIS‘I' LAYER

Figure 87. Diamond growth on the diamond-seeded photoresist layer showing lateral
growth; a) the CVD diamond sensor (thermistor) by the lithography-based
patterning, b) resolution on its edge, e) lateral growth in the reactor and d)
illustration for the diamond growth.

180

LASER BEAM SPOT
DIAMETER: 80 um

     

250 pm 550 pm 250 um

Figure 88. Drawing scheme, i.e., translation scheme for the micro-CNC stage, for the
maskless patterning on CVD diamond ﬁlm.

The application of the CVD diamond ﬁlm to the micro—sensors usually requires the
isolated-cell patterning for electrical wiring. A pattern on a CVD diamond ﬁlm is
fabricated to verify the feasibility of the maskless ablation process. The average grain
size and vertical thickness of the subjected diamond ﬁlm (BW062) was 2 um and 4 urn,
respectively. The argon gas streaming at 4.72x10‘4 m3/sec was used with the laser
irradiance at 6x108 W/cm2 and the repetition rate at 10 Hz. To create a rectangular
isolated—cell—pattem, a programmed translation was designed by drawing six
consecutively decreasing rectangles. Figure 88 show the illustration for the drawing

scheme, in which the micro-CNC stage is translated to the programmed positions.

181

 

Figure 89. Isolated cell-pattem on a CVD diamond ﬁlm by the excimer laser maskless
patterning process, a) the isolated cell-pattem, b) magniﬁed view on the cell
edge.

In the drawing scheme, the 250 um wide frame was ablated by the programmed
translation with overlapping of 80 um diameter laser spot. The translation speed of X
and Y motion stage was constant at 200 uni/sec. The software program for the motion
stage control is composed by the QuickBasic, Microsoft, and listed in Appendix A. After
the ablation process, the surface was cleaned by boiling (~ 200°C) in 1:1 solution of Cr03
and H2804 for 2 minutes.

The patterned CVD diamond ﬁlm is shown in Figure 89a. The patterned cell of
550x450 um2 is isolated from its matrix. The cell-pattemed CVD diamond ﬁlm shows
the feasibility of the maskless patterning on ultra-hard ﬁlm materials. In Figure 89b, one
of the cell edges is magniﬁed to show its linearity. The roughness of the cell edges was
caused by the series of pulsed irradiation with the circular spot and vibration from the

micro-CNC stage. The vibration from the micro-CNC can be solved by improving the

182

resolution of the motion stage. The components for the high-resolution motion stage are

commercially available from various sources.

6.1.2. Maskless patterning in various gas processing conditions

The maskless ablation process for the isolated-cell pattern was compared among
the various gas processing conditions, such as the ambient air, the helium gas-streaming,
and the argon gas-steaming. The drawing scheme, the processing parameters and the
surface cleaning procedure were the same as those described in Section 6.1.1. Figure 90
shows the patterns, fabricated under the gas processing conditions. Even after the
chemical cleaning for the removal of the carbon debris and amorphous graphite layers,
the isolated-cell pattern processed in the ambient air in Figure 90a showed the halo-like
band (indicated by the arrow) around the ablated area. No visible change was observed
around the patterns processed under the helium gas-streaming (Figure 90b), and the argon
gas-streaming (Figure 90c). The halo-like band, observed in the ambient air, was
examined by the Raman spectroscopy (Kaiser Optical Systems, Holo Probe). The same
locations in other processing conditions were examined by the Raman spectroscopy for
comparison. The arrows in Figure 90 indicate the positions for the detection of the
Raman spectra. Figure 91 shows the Raman spectra on the indicated positions around the
cell patterns. The halo-like band in ambient air showed a relatively small intensity in the
observed range including the diamond spectrum at1332 cm", as compared to the argon
and helium gas-streaming conditions. No significant difference was found in the Raman

spectra between the helium and argon gas streaming conditions.

183

 

Figure 90. Maskless ablation process for the isolated-cell pattern in the various gas
processing conditions; a) ambient air, b) helium gas streaming, and c) argon
gas streaming. The arrows indicate the positions for the detection of Raman
spectrum in Figure 91.

184

 

 

 

 

 

200
I
1‘
~15o- ' ”
5 «ll
: .
3
a M
i!
5 100- ‘1
3 nanometre-IR ‘7'”
a. - (w \
55. ”4“”"0‘0 mm
.5 50- x. ”*0",
ambient-Ir
o I I I I I l I I I
1000 1200 1400 1600 1800 2000

wavenumber (cm")

Figure 91. Raman spectra on the isolated-cell patterns, processed in the various gas
processing conditions.

It is conclusive from the observations that the halo-like band in the ambient air is
the plasma-affected zone (PAZ), in which the sp3 bondings in the diamond surface might
be partially transformed to sp2 bondings. The formation of the sp2 bondings alters the

conductivity of the fabricated pattern [75], which is detrimental for the sensor

applications.

185

 

 

 

 

Figure 92. A magniﬁed view of a complicated patterning on the diamond ﬁlm showing
the emblem of the Michigan State Univeristy, the Spartan helmet and the
letters, MSU.

6.1.3. Processing for complicated, and large patterns

The feasibility of the maskless processing system for large, and complicated
patterns, was demonstrated on the diamond ﬁlm. The average grain size and vertical
thickness of the subjected diamond ﬁlm (BW097) was 2 pm, and 6 um, respectively.
The helium gas-streaming at 4.72X10'4 m3/sec was used with the laser energy ﬂuence at
7.2x108 W/cm2 and the repetition rate at 10 Hz. In the drawing schemes, the translation
speed of X and Y motion stage was constant at 200 uni/sec.

Figure 92 shows the complicated patterning on the diamond ﬁlm, which was
engraved with the emblem of the Michigan State Univeristy, the Spartan helmet and the

letters.

186

 

Figure 93. Fabrication of three isolated-cell patterning on the diamond ﬁlm by the
maskless ablation technique.

The spot size used for the patterning was 80 um. Figure 93 shows the three isolated-cell
patterning in millimeter scale. The multi-cell sensors are common for the signal
averaging and multifunctional censors [122]. Three 1x1.5 mm2 cells were ablated by the
programmed translation with overlapping of 175 um diameter laser spot. The software
programs, written by the QuickBasic, for the patterns are listed in Appendices B and C.

These complicated patterns in millimeter scale verify the versatility of the patterning and
the capability of the rapid prototyping for the MP-I maskless patterning system in this

study.-

6.1.4. Fabrication of diamond lens by maskless patterning process

Diamond has great potential for the application to the optical and x-ray windows

due its excellent transparency to the electromagnetic waves [3, 4, 53]. The application

187

for the windows involves micromachining of the freestanding CVD diamond ﬁlms into
required lens geometry.

To demonstrate the feasibility for the thick ﬁlm micromachining, the 3.5 mm
diameter diamond lens was fabricated by the maskless patterning system. The
freestanding thick CVD diamond ﬁlm (ST204), average thickness 270 um, and average
grain size 40 um, was used to fabricate the circular diamond lens. The substrate side of
the freestanding diamond ﬁlm, which retained ﬂatness similar to the polished silicon
wafer, was exposed to the laser irradiation. The ablation process was performed in the
ambient air with the laser irradiance at 7.2><103 W/cm2 and pulse repletion rate at 10 Hz.
The spot size used for the drawing circle was 175 um, and the micro-CNC was
programmed for the continuous circular movement. The software programs, written by
the QuickBasic, for the circular pattern is listed in Appendix D. The cutting of the thick
diamond ﬁlm for the lens required 1.74x10s laser pulses, which took 4.8 hours of the
laser irradiations. Figure 94 shows the diamond lens fabricated by the maskless
patterning system. The pattemed-cut diamond lens is shown in Figure 94a, in which the
substrate side of the diamond lens is exhibited. The other side of the lens, i.e., the side
with the polycrystalline diamond growth, retains the same roughness as the diamond ﬁlm.
Figure 94b shows the smooth surface of the circular lens and the ablation-cut hole in its
matrix. Figure 94c presents the micromachined edge of the lens, which shows the clean-
cut by the laser ablation.

The diamond lens in square geometry was also demonstrated by the maskless
patterned cut. The freestanding CVD diamond ﬁlm (ST235), average thickness 110 um

and average grain size 50 um, was used to fabricate the square diamond lens.

188

L1

.MJDLLNS

 

Figure 94. Fabrication of the CVD diamond lens from the thick ﬁlm micromachining by
the maskless patterning system; a) 3.5 mm diameter diamond lens cut from
the freestanding diamond ﬁlm, b) the diamond lens, 0) cutting edge of the
lens.

189

I f
z
/

j y - .
SU‘U/IPE PM TE RNED CUT h"
DIAMOND [CNS

 

Figure 95. Square pattemed-cut diamond lens which is placed over the laser cut hole.

The micro-CNC was programmed for the continuous square movement. The software
programs, written by the QuickBasic, for the square pattern is listed in Appendix B. All
other processing parameters were the same as the circular diamond lens process. Figure
95 show the 3x3 mm2 pattemed-cut diamond lens, in which the side with the diamond
growth was exhibited. The square lens was displayed over the laser cut hole in the
matrix. The number of laser pulses required for the square patterned cutting was 6.1x104

pulses, which needed 1.7 hour of the laser irradiations.

6.1.5. Contour patterning on CVD Diamond Films

Contour patterning is one of the hardest patterning techniques in the lithography-

based processing. In the MP-I maskless patterning system, the rotate and tilt stages allow

190

the target translation in 3 dimensional directions. The proper alignment with the incident
laser pulses makes the contour patterning possible in our MP-I system.

To demonstrate the feasibility for the contour patterning, the circular contour-
track was fabricated by the maskless patterning system. The freestanding thick CVD
diamond ﬁlm (ST204), average thickness 270 um and average grain size 40 um, was
used to pattern the contour-track. The substrate side of the freestanding diamond ﬁlm,
which retained ﬂatness similar to the polished silicon wafer, was exposed to the laser
irradiation. The ablation process was performed in the ambient air with the laser
irradiance at 7.2x108 W/cm2 and pulse repletion rate at 10 Hz. The translation speed of
the rotation stage was 11 °/sec. The software programs, written by the QuickBasic, for
the pattern is listed in Appendix F. The contour patterning took 1.2x104 laser pulses,
which took 20 minutes of the laser irradiations. A rectangular spot size in 250x400 |.l.m2
was used with the rotation and tilt stages. The drawing scheme for the circular contour-
track is shown in Figure 96. The target normal was tilted by 40° degrees towards the
direction for the incident laser beam. The angular irradiation on the tilted specimen
creates the inhomogeneous ablation depth across the spot size, as shown in the inset of
Figure 96. The depth ablation rate is gradually changed from larger, in the upper region
the laser spot, to smaller in the lower region of the laser spot. The inhomogeneous
ablation with rotation of the specimen results in the circular concave tack on the
freestanding diamond ﬁlm. Figure 97a shows the overview of the circular contour-tack,
which exhibits the consistent contour pattern with good symmetry. The area around the

center edge is magniﬁed in Figure 97b, which shows roughness of the laser ablated area.

191

CENTER OF LASER IRRADIATION

 

   
 

[CENTER OF ROTATION

 

=-__—_:_—_->

‘DIAMOND FILM

 

 

 

ROTATION STAGE

 

 

 

 

Figure 96. Schematic diagram for the patterning of the circular contour track, using
rotation and tilt stages.

 

Figure 97. Circular contour-track on the freestanding diamond ﬁlm by using rotation and
tilt stages; a) overview of the circular contour-track, and b) magniﬁed view of
the edge area.

192

6.2. Chapter Summary

The conventional machining and lithography-based patterning on the CVD
diamond ﬁlm are difﬁcult due to the high wear resistance and the chemical inertness.
The innovative maskless patterning technique, developed in this work, employs pulsed
irradiation of focused laser beam on a target material, which is translated to the
programmed positions by the micro-CNC. To produce micro patterns and structures using
laser ablation, the MP-I maskless patterning system has been constructed in the High
Energy Laser Processing Laboratory at MSU. Using maskless patterning system, micro-
pattems can be developed on diamond ﬁlms through the direct ablation without masking
technique. In this chapter, the feasibility of the maskless patterning on the CVD diamond
ﬁlm was clearly demonstrated. The demonstration includes the fabrication of the
isolated-cell patterns, and the patterned engravings of MSU and its emblem on diamond
ﬁlms. The patterned cut for diamond windows, and the contour patterning shows
extensive capabilities of the MP—I system. The maskless patterning, developed in this
study, has great potential to introduce the CVD diamond ﬁlm to the various applications,
such as semiconductor devices, sensors, optical windows and microelectromechanical
systems (MEMS). This maskless patterning addresses the current process-intensive,
lithography-based patterning. Along with its advantages of a simple setup and a direct
process, the maskless process makes the rapid prototyping possible for patterns on the

CVD diamond ﬁlm.

Chapter VII

CONCLUSION

The excellent mechanical and electrical properties make CVD diamond ﬁlms
uniquely qualiﬁed for the applications, such as integrated circuits, sensors, optical
windows and MEMS. To utilize the excellent properties of the diamond ﬁlms in the
applications, micromachining and patterning of diamond ﬁlms are primarily required.
The excimer lasers have shown their capabilities in polishing, etching, and patterning of
CVD diamond ﬁlm. However, the processes have exhibited some damage, which has
been obstacle to the application of laser ablation process to CVD diamond.

To overcome current barriers of the laser ablation process on CVD diamond,
technical and fundamental investigations were performed in this study. In this respect,
this study mainly focuses on i) macroscopic and microscopic analysis of laser-diamond
coupling, and ii) analysis on the laser-induced plasma and its interaction to surrounding.
These fundamental aspects in this study were linked to practical fabrication of patterned
diamond components by the innovative maskless patterning technique.

The laser-diamond interaction was examined by subjecting the diamond ﬁlm
under three different processing environments, such as the ambient air, the vacuum
condition and the gas-streaming conditions. By the dissipation of the high temperature
plasma off from the surface, the inert gas-streaming showed a good feasibility for the

precise micromachining of diamond ﬁlms.

193

194

The ablation rate of the CVD diamond ﬁlm was obtained by measuring the
ablation depth as a function of the number of laser pulses and the laser irradiance. The
measured ablation rates were compared among the gas processing conditions, such as the
ambient air, helium gas and argon gas, respectively. No signiﬁcant difference was found
on the ablation rate among the gas processing environments. Approximately a linear
relationship was observed between the ablation depth and the number of laser pulses, and
between the ablation depth and the laser irradiance. Based on these observations, linear
and nonlinear models for the ablation process were proposed. The nonlinear model
accounted for the divergence of the focused laser beam, and resultant decrease in the
laser irradiance. The nonlinear modeling proposed the number of the laser pulses as the
third order polynomial function of the ablation depth.

The initial stage of the laser-diamond interaction was observed by the AFM and
Raman spectroscopy. It could be speculated from the AFM observation that the
preferential interaction by the edge-chipping-off mechanism occurs at the very initial
stage with in 1 to 2 laser pulses. Then, the successive laser irradiation reduces the surface
roughness in overall smoothening-out mechanism. It was reasonably conclusive from the
Raman spectroscopy observation that the laser-diamond interaction causes the formation
of the graphitized surface micro-layer within a few pulsed irradiations. Then, the self-
sustaining graphite layer absorbs the successive laser pulses for the ablation, and the
surface morphology evolves according to the ablation.

To examine the evolution of the surface morphology beyond the initial
interaction, in-situ observation was performed for the laser irradiation on the CVD

diamond ﬁlm. The sharp edges and vertexes exhibited higher etching rate than the planes

195

and valleys. The roughness reduction was caused by the uneven etching on the jagged
polycrystalline diamond crystals. The uneven etching ratio is explained by the
overheating of the crystal edges and vertexes due to the laser irradiation.

Laser-induced plasma on the CVD diamond ﬁlm was investigated by analytic
instrumentations, such as laser-induced breakdown spectroscopy, and time-integrated
plasma image capturing. The characteristics in emission spectra, among the gas
processing environments, were examined by the LIBS observations. The plasma
emission spectra in the ambient air exhibited very strong CN Violet bands and the lowest
C2 Swan bands. In contrast, the argon gas-streaming shows the strongest C2 Swan band
emissions with signiﬁcantly reduced CN Violet bands. The helium gas processing
condition shows the lowest CN Violet band emissions with higher C2 Swan bands than
those of ambient air. As compared to the molecular spectra, relatively weak emission
signals of the neutral carbon, and the singly ionized atom were identiﬁed. In the
observations on environmental gas breakdown, the atomic emission route of nitrogen and
oxygen is supported by the absence of molecular emission spectra, and the presence of
atomic emission spectra. The breakdown of argon gas was observed by the intense argon
neutral emission spectra, but no indication of helium gas breakdown was observed. The
mechanisms for the major spectral emissions are discussed, and most plausible
mechanisms are proposed in this study.

The excitation temperatures of the plasma are deduced by the Boltzmann-plot
method in which LTE of the plasma was assumed. The excitation temperatures are
calculated by emission intensity ratios from different upper energy levels of an element in

the same electronic state. The plasma in ambient air showed the highest excitation

196

temperature proﬁle, while the argon gas-streaming showed the lowest proﬁle. Electron
densities are calculated from the proportionality between the Stark effect on the line
broadening and the electron population. The calculated electron densities in various gas
processing conditions are presented as a function of the laser irradiance. In the given
range of the laser irradiance, all gas processing conditions exhibited an increase in the
electron densities as the laser irradiance increased. The densest population of electrons
was found in the density proﬁle of the ambient air. The argon gas-streaming showed the
lowest density proﬁle among the processing conditions.

Time-integrated images, in the ambient air showed the lowest longitudinal
expansion of the plasma. In contrast, the lateral expansion of the plasma is relatively
strong. The lateral expansion is prominent in ambient air, which showed the hottest and
densest plasma among the gas processing conditions. The plasma images for the helium
gas processing showed more spherical-type expansion than that for the other gas
processing conditions. The low density of helium, which creates lowest conﬁnement
among the processing environments, could explain the spherical expansion of the plasma.
The largest extent of the plasma, in both the lateral and longitudinal directions, was
observed in the argon gas-streaming. The largest extent of the plasma in the argon gas-
streaming is mainly due to the very intense spectral emissions from argon and the C2
Swan bands. The carbonitride formation in the ambient air is mainly responsible for the
smallest plasma formation.

The conventional machining and lithography-based patterning on the CVD
diamond ﬁlm are difﬁcult due to the high wear resistance and the chemical inertness.

The innovative maskless patterning technique, developed in this work, employs pulsed

197

irradiation of focused laser beam on a target material, which is translated to the
programmed positions by the micro-CNC. To produce micro patterns and structures
using laser ablation, the MP-I maskless patterning system has been constructed in the
High Energy Laser Processing Laboratory at MSU. The innovative maskless patterning
technique employs pulsed irradiation of a focused laser beam on a target material, which
is translated to the programmed positions by a micro computer numerical controlled
(micro-CNC) stage. The feasibility of the maskless patterning on the CVD diamond ﬁlm
was clearly demonstrated. The demonstration includes the fabrication of the isolated-cell
patterns, and the patterned engravings of MSU and its emblem on diamond ﬁlms. The
patterned cut for diamond windows, and the contour patterning shows extensive
capabilities of the MP—I system. The maskless patterning, developed in this study, has
great potential to introduce the CVD diamond ﬁlm to the various applications, such as
semiconductor devices, sensors, optical windows and microelectromechanical systems
(MEMS). This maskless patterning addresses the current process-intensive, lithography-
based patterning. Along with its advantages of a simple setup and a direct process, the
maskless process makes the rapid prototyping possible for patterns on the CVD diamond
ﬁlm. The maskless patterning introduces CVD diamond ﬁlms to new area of sensors,

optical windows, integrated circuits and MEMS, where extreme tolerance of a material is

required.

APPENDICES

198

199

APPENDIX A

Soﬁyare program [or the motion stage control, composed by the QuickBasic, Microsoﬂ.

- Isolated-cell pattern in Figure 88

'$INCLUDE: 'IS_BC.BI' 'enables instep library
'SINCLUDE: 'QB.BI'

'Main Body
CALL ischeckcard(592, checkcode%) 'checks to see it card is present
IF checkcode% = 0 THEN
PRINT “Card not found.”
END
END IF

CALL issetcardtype(1) 'sets the card type to QuickPhase half stepping mode
CALL issetcplane(1, 2) 'defines x and y axes for drawing arcs

st = 10 'sets size factor
CALL ispowerinit(10) 'sets power level (to 20%)
speed% = 50 'speed in steps per second

'delay% = 2000000 I speed% 'calculates delay between steps for speed setting
CALL issetspeed(32767) 'sets stepper motor speed to min. steps per second
CALL issetmode(0) 'sets motion stage to relative mode
PRINT “Starting Movement"
CALL issetspeed(2000) 'shutter speed
CALL ismover(0, 0, -365, 0, exitcode%)'open shutter
CALL issetspeed(32767) 'drawing speed
FOR c = 0 TO 4
CALL ismover(o, -(24 - 2 * c) ' st, 0, 0, exitcode%)
CALL ismover((22 - 2 * c) * st, 0, 0, 0, exitcode%)
CALL ismover(o, (24 - 2 * c) " sf, 0, 0, exitcode%)
CALL ismover(-(22 - 2 ' c) * st, 0, 0, 0, exitcode%)
IF c <> 4 THEN CALL ismover(1 " sf, -1 * sf, 0, 0, exitcode°/e)
NEXT c
CALL issetspeed(2000) 'shutter speed
CALL ismover(O, 0, 365, 0, exitcode%)‘closes shutter
PRINT "Block Drawn"
CALL issetspeed(20000) 'spacing speed
CALL ismover(-4 * sf, 4 * sf, 0, 0, exitcode°/e)
PRINT "Program Done"
END

200

APPENDIX B

Sommre program for the motion stage control, composed by the QuickBasic, Microsoﬂ.

- MSU and its emblem (Sparty helmet) in Figure 92

DECLARE SUB cap (sfl, delay°/e)

DECLARE SUB support (sﬂ, delay°/o)
DECLARE SUB plume (si!, delay°/e)

DECLARE SUB closeshutter (delay%)
DECLARE SUB openshutter (delay°/o)
'SINCLUDE: 'IS_BC.BI' 'enables instep library
'$lNCLUDE: 'QB.BI'

'Main Body
a = 1
b = 1
WHILE a = 1
CALL ischeckcard(592, checkcode%) 'checks to see if card is present
lF checkcode% = 0 THEN
PRINT "Card not found.“
INPUT 'Do you wish to try again (1=yes,0=no)"; b
ELSE a = 0
END IF
IFb=0THENa=0
WEND
IF b = 0 THEN END

CALL issetcardtype(1) 'sets the card type to QuickPhase half stepping mode
CALL issetcplane(1, 2) 'defines x and y axes for drawing arcs

sf = 12 'sets size factor

CALL ispowerinit(10) 'sets power level (to 20%)

'speed% is speed in steps per second

'delay% = 2000000 / speed% 'calculates delay between steps for speed setting
delay% = 32767

CALL issetspeed(delay%) 'sets stepper motor speed to speed steps per second
CALL issetmode(0) 'sets motion stage to relative mode

PRINT "Starting Movement“

CALL plume(sf, delay%)

CALL issetspeed(20000) 'sets to spacing speed
CALL ismover(13 " sf, -28 * st, 0, 0, exitcode%)
CALL support(st, delay°/o)

CALL ismover(1 ' st, 3 * sf, 0, 0, exitcode%)
CALL cap(sf, delay°/o)

PRINT "Returning to Original Position'

CALL ismover(-45 * st, 49 * sf, 0, 0, exitcode%)

SUB cap (sf, delay°/e)
CALL openshutter(delay°/o)
CALL ismover(1 " st, 0, 0, 0, exitcode%)

201

CALL ismover(0, 1 * 31,0, 0, exitcode%)

CALL ismover(s * sf, 0, 0, 0, exitcode%) 'to b
CALL ismover(4 " st, 1 * st, 0, 0, exitcode%)
CALL ismover(2 " st, 1 * sf, 0, 0, exitcode%)
CALL ismover(3 ' sf, 2 * st, 0, 0, exitcode%) 'to 0
CALL ismover(3 ' sf, 3 * sf, 0, 0, exitcode%)
CALL ismover(2 * sf, 3 * sf, 0, 0, exitcode%)
CALL ismover(3 " st, 6 ' sf, 0, 0, exitcode%)
CALL ismover(2 * sf, 6 " st, 0, 0, exitcode%)
CALL ismover(1 * st, 2 ' sf, 0, 0, exitcode%)

CALL ismover(1 * st, 3 * st, 0, 0, exitcode%)

CALL ismover(2 " sf, 4 ' st, 0. 0, exitcode%)

CALL ismover(3 " st, 4 ' sf, 0, 0, exitcode%)

CALL ismover(-4 ' st, -2 " st, 0, 0, exitcode%)

CALL ismover(-4 " st, 0, 0, 0, exitcode%)

CALL ismover(o, -8 ' st, 0, 0, exitcode%)

CALL ismover(-2 " st, -4 * st, 0, 0. exitcode%)

CALL ismover(-2 " st, -1 * sf, 0, 0, exitcode%) 'to d
CALL ismover(-1 ‘ st, -1 " sf, 0, 0, exitcode%)

CALL ismover(-2 ' st, 0, 0, 0. exitcode%)

CALL ismover(O, -1 * sf, 0, 0, exitcode%)

CALL ismover(-3 ' s1, 0, 0, 0, exitcode%) ‘to e
CALL ismover(O, 1 * sl, 0, 0, exitcode%)

CALL ismover(-3 ' st, 0, 0, 0, exitcode%)

CALL ismover(O, 1 ' st, 0, 0, exitcode%)

CALL ismover(-2 * sf, 0, 0. 0. exitcode%)

CALL ismover(O, 1 * sf, 0, 0, exitcode%)

CALL ismover(-1 ‘ sf, 0, 0, 0, exitcode%)

CALL ismover(0, 1 " 81.0, 0,exitcode%) 'tof

CALL ismover(o, 1 ' st, 0, 0. exitcode%)

CALL ismover(1 " st, 0, 0, 0, exitcode%)

CALL ismover(o, 1 " sf, 0, 0, exitcode%)

CALL ismover(1 * sf, 0, 0, 0, exitcode%)

CALL ismover(O, 1 ' st, 0, 0, exitcode%)

CALL ismover(2 ' st, 0, 0, 0, exitcode%)

CALL ismover(o, 1 " st, 0, 0, exitcode%)

CALL ismover(3 ‘ st, 0, 0, 0, exitcode%)

CALL ismover(O, 1 " sf, 0, 0, exitcode%)

CALL ismover(2 * st, 0, 0, 0, exitcode%) 'to 9

CALL ismover(0, -1 " sf, 0, 0, exitcode%)

CALL ismover(o, 1 ' sf, 0, 0, exitcode%)

CALL ismover(3 " st, 0, 0, 0, exitcode%)

CALL ismover(O, 2 "’ sf, 0, 0, exitcode%)

CALL ismover(-1 ' st, 1 * 51,0, 0, exitcode%)

CALL ismover(O, 10 ‘ sf, 0, 0, exitcode%) 'to (64.74)
CALL ismover(1 * sf, 0, 0, 0, exitcode%)

CALL ismover(O, 7 " sf, 0, 0, exitcode%)

CALL ismover(1 ’ st, 1 " sf, 0, 0, exitcode%)

CALL ismover(O, 4 * sf, 0, 0, exitcode%)

CALL ismover(1 " st. 1 * sf, 0, 0, exitcode%)

CALL ismover(O, 2 " sf, 0, 0, exitcode%) “to h

CALL closeshutter(20000)

CALL ismover(4 * st, -2 * sf, 0, 0, exitcode%)
trademark

CALL openshutter(delay%)

CALL ismover(1 ‘ sf, 0, 0, 0, exitcode%)

202

CALL ismover(O, 2 * sf, 0, 0, exitcode%)

CALL ismover(O, -2 ' sf, 0, 0, exitcode%)

CALL ismover(1 ' st, 0, 0, 0, exitcode%)

CALL closeshutter(20000)

CALL ismover(1 " sf, 2 * sf, 0, 0, exitcode%)
CALL openshutter(delay%)

CALL ismover(o, -2 ' sf, 0, 0, exitcode%)

CALL ismover(1 ' sf, 0, 0, 0, exitcode%)

CALL ismover(o, 1 ‘ sf, 0,0, exitcode%)

CALL ismover(o, -1 * sf, 0, 0, exitcode%)

CALL ismover(1 * sf, 0, 0, 0, exitcode%)

CALL ismover(O, 2 ‘ sf, 0, 0, exitcode%)

CALL closeshutter(20000)

'end of trademark

'back to cap at h

CALL ismover(-9 * sf, 0, 0, 0, exitcode%)

CALL openshutter(delay%)

CALL ismover(O, -1 " sf, 0, 0, exitcode%)

CALL ismover(-2 * sf, 0, 0, 0, exitcode%)

CALL ismover(-3 " st, -1 * st, 0, 0, exitcode%)
CALL ismover(-4 " s1, -2 * sf, 0, 0, exitcode%)
CALL ismover(-3 ' sf, -2 * sf, 0, 0, exitcode%) 'to i
CALL ismover(4 ' sf, -3 " st, 0, 0, exitcode%)
CALL ismover(-4 ' sf, -4 " sf, 0, 0. exitcode%) ‘toj
CALL ismover(4 ‘ sf, -1 * sf, 0, 0, exitcode%)
CALL ismover(-1 * sf, 0, 0, 0, exitcode%)

CALL ismover(4 * sf, 1 " sf, 0, 0, exitcode%) 'to k
CALL ismover(-6 " sf, 0, 0, 0, exitcode%)

CALL ismover(-6 * sf, 2 " sf, 0, 0, exitcode%)
CALL ismover(-2 * sf, 1 " st, 0, 0, exitcode%)
CALL ismover(-1 * sl, 0, 0, 0, exitcode%) 'tol
CALL ismover(1 " sf, -1 ' sf, 0, 0, exitcode%)
CALL ismover(1 " st, -3 * st, 0, 0, exitcode%)
CALL ismover(0, -9 " sf, 0, 0. exitcode%) 'to m
CALL ismover(-2 " st, -8 * sf, 0, 0, exitcode%)
CALL ismover(o, -9 * sf, 0, 0, exitcode%) ‘to n
CALL ismover(1 ' st, -3 ' sf, 0, 0, exitcode%)
CALL ismover(2 " sf, -4 " st, 0, 0, exitcode%) 'to 0
CALL ismover(S " st, -5 ' sf, 0, 0, exitcode%)
CALL ismover(4 * sf, -2 * sf, 0, 0, exitcode%)
CALL ismover(3 * sl, -1 ' st. 0, 0, exitcode%)
CALL ismover(5 " st, 0, 0, 0, exitcode%)

CALL ismover(O, -1 * st, 0, 0, exitcode%) “to (45.33)
CALL closeshutter(20000)

PRINT 'helmet done“

END SUB

SUB closeshutter (delay°/o)

CALL issetspeed(2000) 'sets shutter speed
CALL ismover(O, 0, 365, 0, exitcode%) 'closes shutter

CALL issetspeed(delay%) 'resets speed to previous value

END SUB

SUB openshutter (delay%)

CALL issetspeed(2000) 'set to shutter speed
CALL ismover(O, 0, -365, 0, exitcode%) 'open shutter

203

CALL issetspeed(delay%) 'retum speed to previous value
END SUB

SUB plume (sf, delay°/e)
CALL openshutter(delay%)
CALL ismover(4 ‘ sf, -4 ’ sf, 0, 0, exitcode%) 'to A
'CALL ismover(O, -1 " sf, 0, 0. exitcode%) '1
‘CALL ismover(1 * 31,0, 0, 0, exitcode%) '2
'CALL ismover(o, -2 * st, 0, 0, exitcode%) '3
'CALL ismover(1 * sf, 0, 0, 0, exitcode%) '4
'CALL ismover(o, -1 * sf, 0, 0, exitcode%) '5
'lines 1-5 could likely be replaced by
CALL ismover(2 " sf, --4 ‘ sf, 0, 0, exitcode%) 'was comment
CALL ismover(O, ~12 " sf, 0, 0, exitcode%) “to B
CALL ismover(O, -1 * sf, 0, 0, exitcode%)
'CALL ismover(-1 * sf, 0, 0, 0, exitcode%)
'CALL ismover(O, -4 * sf, 0, 0, exitcode%)
'CALL ismover(-1 * sf. 0, 0, 0, exitcode%)
'CALL ismover(o, -4 * st, 0, 0, exitcode%)
'CALL ismover(-1 * sf, 0, 0, 0, exitcode%)
'CALL ismover(O, -4 * sl, 0, 0, exitcode%)
'CALLismover(-1 ’ sf, 0, 0, 0, exitcode%)
CALL ismover(4 ' st, -12 ' sf, 0, O, exitcode%) 'was added...
CALL ismover(o, -12 * sf, 0, 0, exitcode%) ‘to C
'CALL ismover(O, -3 " sf, 0, 0, exitcode%)
'CALL ismover(1 * sf, 0, 0, 0, exitcode%)
'CALL ismover(O, 2 ' sf, 0, 0, exitcode%)
'CALL ismover(-1 * sf, 0,0, 0, exitcode%)
'CALL ismover(o, -1 * st, 0, 0, exitcode%)
'CALL ismover(1 " sf, 0, 0, 0, exitcode%)
'CALL ismover(o, -3 " sf, 0, 0, exitcode%) 'to D old
CALL ismover(1 ‘ sf, -5 * 81,0, 0, exitcode%) 'to D
'CALL ismover(o, -2 “ sf, 0, 0, exitcode%)
'CALL ismover(1 * sf, 0, 0, 0, exitcode%)
'CALL ismover(O, 1 * sf, 0, 0, exitcode%)
'CALL ismover(-1 ' st, 0, 0, 0, exitcode%)
'CALL ismover(1 " sf, -1 ' sf, 0, 0, exitcode%)
'CALL ismover(o, -3 " st, 0, 0, exitcode%)
'CALL ismover(1 ' sf, 0, 0, 0, exitcode%)
'CALL ismover(o, 1 * s1, 0, 0, exitcode%)
'CALL ismover(-1 " st, 0, 0, 0, exitcode%)
'CALL ismover(1 " st, -1 * sf, 0, 0, exitcode%)
'CALL ismover(O, -2 * sf, 0, 0, exitcode%) 'to E old
CALL ismover(1 * st, -4 * sf, 0, 0, exitcode%)
CALL ismover(1 ' sf, -3 * st, 0, 0, exitcode%) 'to E
'CALL ismover(1 " sf, 0, 0, 0, exitcode%)
'CALL ismover(0, -2 " st, 0, 0, exitcode%)
'CALL ismover(1 ' sf, 0, 0, 0, exitcode%)
'CALL ismover(O, -2 * st, 0, 0, exitcode%)
'CALL ismover(1 " sf, 0, 0. 0, exitcode%)
'CALL ismover(O, -1 " st, 0, 0, exitcode%)
'CALL ismover(1 * st, 0, 0, 0, exitcode%)
'CALL ismover(O, -1 ' sf, 0, 0, exitcode%)
'CALL ismover(1 * sf, 0, 0, 0, exitcode%)
'CALL ismover(o, -2 * st, 0, 0, exitcode%)
'FOR x = 1 TO 4

204

' CALL ismover(1 ' 81,0,0,0,BX1100dB°/o)
' CALL ismover(O, -1 ‘ $1.0, 0, exitcode%)
'NEXT

'CALL ismover(1 " st, 0, 0, 0, exitcode%)
'CALL ismover(o, 1 * st, 0, 0, exitcode%)
'CALL ismover(-1 " st, 0, 0, 0, exitcode%)
'CALL ismover(1 * st, -1 * 81.0.0, exitcode%)
'FOR x = 1 TO 3

' CALL ismover(1 " 31,0, 0,0, exitcode%)
' CALL ismover(O, -1 ' sf, 0, 0, exitcode%)
'NEXT x

'CALL ismover(2 " sf, 0, 0, 0, exitcode%)
'CALL ismover(O, -1 ' sl, 0, 0, exitcode%) 'to F old
CALL ismover(2 " st, -4 * s1, 0, 0, exitcode%)
CALL ismover(3 ‘ st, -4 " sl, 0, 0, exitcode%)
CALL ismover(3 "' sf, -3 * st, 0, 0, exitcode%)
CALL ismover(4 ‘ st, -3 ' sf, 0, 0, exitcode%)
CALL ismover(3 " st, -2 ' sf, 0, 0, exitcode%) “to F
'CALL ismover(1 * st, 0, 0, 0, exitcode%)
'CALL ismover(0, -1 " sf, 0, 0, exitcode%)
'CALL ismover(2 " s1, 0, 0, 0, exitcode%)
'CALL ismover(O, -1 " st, 0, 0, exitcode%)
'CALL ismover(1 " sf, 0, 0, 0, exitcode%)
'FOR x = 1 TO 3

' CALL ismover(O, -1 * st, 0, 0, exitcode%)
' CALL ismover(1 ‘ sf, 0, 0, 0, exitcode%)
' CALL ismover(0, 1 " s1, 0, 0, exitcode%)
' CALL ismover(-1 ' 51.0.0, 0,exitcode%)
' CALL ismover(1 " sf, -1 * st, 0, 0, exitcode%)
' CALL ismover(1 * sf, 0, 0, 0, exitcode%)
'NEXT x

'CALL ismover(1 " sf, 0, 0, 0, exitcode%)
'CALL ismover(o, -1 ‘ st, 0, 0, exitcode%)
'CALL ismover(3 * st, 0, 0, 0, exitcode%)
'CALL ismover(O, -1 ' sf, 0, 0, exitcode%)
'CALL ismover(4 " st, 0, 0, 0, exitcode%)
'CALL ismover(o, -1 * st, 0, 0, exitcode%) 'to G old
CALL ismover(3 ' sf, -2 * st, 0, 0, exitcode%)
CALL ismover(6 * sf, -3 * sl, 0, 0, exitcode%)
CALL ismover(9 * sf, -3 ' sf, 0, 0, exitcode%) 'to G
'CALL ismover(24 * sf, 0, 0, 0, exitcode%)
CALL ismover(23 " st, 0, 0, 0, exitcode%)
'CALL ismover(O, 1 ‘ sf, 0, 0, exitcode%)
'CALL ismover(-1 ‘ sf, 0, 0, 0, exitcode%)
'CALL ismover(0, -1 ' st, 0, 0, exitcode%)
'CALL ismover(1 " st, 0, 0, 0, exitcode%)
'CALL ismover(-1 * sf, 1 * sf, 0, 0, exitcode%)
'CALL ismover(4 ' st, 0, 0, 0, exitcode%)
'CALL ismover(o, 1 " sf, 0, 0, exitcode%)
'CALL ismover(3 * st, 0, 0, 0. exitcode%)
'CALL ismover(0, 1 * sf, 0, 0, exitcode%)
'CALL ismover(-1 * st. 0, 0, 0, exitcode%)
'CALL ismover(0, -1 " st, 0, 0, exitcode%)
'CALL ismover(1 " sf, 0. 0, 0, exitcode%)
'CALL ismover(-1 ‘ sf, 1 ' sf, 0, 0, exitcode%)
'CALL ismover(3 ' sf, 0, 0, 0, exitcode%)

205

'CALL ismover(O, 1 * sf, 0, 0, exitcode%)

'CALL ismover(2 * st, 0, 0, 0, exitcode%)

'CALL ismover(0, 1 ' sf, 0, 0, exitcode%)

'CALL ismover(-1 " st, . , , exitcode%)

'CALL ismover(O, -1 ' st, 0, 0, exitcode%)

'CALL ismover(1 ' sf, 0, 0, 0, exitcode%)

'CALL ismover(-1 * sf, 1 " sf, 0, 0, exitcode%)
'CALL ismover(2 " sf, 0, 0, 0, exitcode%) 'to H old
CALL ismover(9 * st, 3 * sf, 0, 0, exitcode%)

CALL ismover(3 " st, 2 " sf, 0, 0, exitcode%) 'to H
CALL ismover(-7 " st, 14 " st, 0, 0, exitcode%) ‘to I new
'CALL ismover(O, 1 " sf, 0, 0, exitcode%)

'CALL ismover(-1 * sf, 0, 0, 0. exitcode%)

'CALL ismover(0, -1 ‘ sf, 0, 0, exitcode%)

'CALL ismover(1 " sf, 0, 0, 0, exitcode%)

'CALL ismover(-1 " sl, 1 * 51,0,0, exitcode%)

'FOR x = 1 TO 2

' CALL ismover(O. 3 * st, 0, 0, exitcode%)

' CALL ismover(-1 * sf, 0, 0, 0, exitcode%)

' CALL ismover(0, -1 * sf, 0, 0, exitcode%)

' CALL ismover(1 ' sf, 0, 0, 0, exitcode%)

' CALL ismover(o, 1 * sf, 0, 0, exitcode%)

' CALL ismover(-1 ' sf, -1 " sf, 0. 0, exitcode%)
'NEXT x

'CALL ismover(o, 3 " sf, 0, 0, exitcode%)

'FOR x = 1 TO 3

' CALL ismover(4 " 31.0.0, 0, exitcode%)

' CALL ismover(O, 2 * st. 0, 0, exitcode%)
'NEXT x

'CALL ismover(-2 ' sf, 0, 0, 0, exitcode%) ‘to l old
CALL ismover(-2 ' sf, -1 * st, 0, 0, exitcode%)

CALL ismover(-3 " sf, -1 * sf, 0, 0, exitcode%)

'CALL ismover(O, -1 * sf, 0, 0, exitcode%)

'CALL ismover(-2 * 81,0, 0, 0, exitcode%)

'CALL ismover(O, -1 " sf, 0, 0, exitcode%)

'CALL ismover(-3 " sf, 0, 0, 0, exitcode%)

'CALL ismover(O, -1 " sf, 0, 0, exitcode%)

'CALL ismover(-3 " sf, 0, 0, 0, exitcode%)

'CALL ismover(O, -1 ‘ sf, 0, 0, exitcode%)

'CALL ismover(-7 ' st, 0, 0, 0, exitcode%)

'CALL ismover(O, -1 * sf, 0, 0, exitcode%)

'CALL ismover(1 * sf, 0, 0, 0, exitcode%)

'CALL ismover(O, 1 ' 81,0, 0, exitcode%)

'CALL ismover(-1 ‘ st, -1 * sf, 0, 0, exitcode%)
'CALL ismover(-5 * st, 0, 0, 0, exitcode%) “to J old
CALL ismover(-3 " sf, -1 * sf, 0, 0, exitcode%)
CALL ismover(-4 * st, -1 " sf, 0, 0, exitcode%)
CALL ismover(-5 " sf, -1 ' sf, 0, 0, exitcode%)
CALL ismover(-3 ' sf, 0, 0, 0, exitcode%) 'to J new
'CALL ismover(O, 1 * $1.0, 0, exitcode%)

'CALL ismover(-8 " sf, 0, 0, 0, exitcode%)

'CALL ismover(o, 1 " st, 0, 0, exitcode%)

'CALL ismover(-4 ' st, 0, 0, 0, exitcode%)

'CALL ismover(O, 1 * st, 0, 0, exitcode%)

'CALL ismover(1 ' st, 0, 0, 0, exitcode%)

'CALL ismover(o, -1 " st, 0. 0, exitcode%)

206

'CALLismover(-1 " sf, 1 * sf, 0, 0, exitcode%)

'FORX=1TO4

' CALL ismover(-2 * sf, 0, 0, 0, exitcode%)
' CALL ismover(o, 1 " st, 0, 0, exitcode%)

’NEXT x
'FOR x = 1 TO 2

' CALL ismover(-1 * st, 0, 0, 0, exitcode%)
' CALL ismover(O, 1 * sf, 0, 0, exitcode%)

'NEXT x

'CALL ismover(-2 ' sf, 0, 0, 0, exitcode%)
CALL ismover(-6 * sl, 1 * sf, 0, 0, exitcode%)
CALL ismover(-5 " sf, 1 * sf, 0, 0, exitcode%)
CALL ismover(-3 * sf, 1 " sf, 0, 0, exitcode%)
CALL ismover(-8 * s1, 4 ' st, 0, 0, exitcode%)
CALL ismover(-3 * st, 2 * st, 0, 0, exitcode%)
'FOR x = 1 TO 3

' CALL ismover(O, 1 ' st, 0, 0, exitcode%)
' CALL ismover(-1 * st, 0, 0, 0, exitcode%)

'NEXT x

'CALL ismover(O, 2 "’ sf, 0, 0, exitcode%)
'CALL ismover(-1 * st, 0, 0, 0, exitcode%)
'FOR x = 1 TO 2

' CALL ismover(o, 1 ' sf, 0, 0, exitcode%)
' CALL ismover(-1 * sf, 0, 0, 0, exitcode%)

'NEXT x
'FOR x = 1 TO 3

‘ CALL ismover(o, 2 * sf, 0, 0, exitcode%)
' CALL ismover(-1 * st, 0, 0, 0, exitcode%)

'NEXT x

'CALL ismover(O, 3 * st, 0, 0, exitcode%)
'CALL ismover(-1 * st, 0, 0, 0, exitcode%)
CALL ismover(-3 * st, 3 * sf, 0, 0, exitcode%)
CALL ismover(-3 ’ sf, 4 ' sf, 0, 0, exitcode%)
CALL ismover(-3 * st, 6 " sf, 0, 0, exitcode%)
CALL ismover(-1 ' sf, 3 * sf, 0, 0, exitcode%)
'CALL ismover(O, 4 " sf, 0, 0, exitcode%)

'CALL ismover(-1 * sf, 1 * sf, 0, 0, exitcode%)

'CALL ismover(0, 5 * sf, 0, 0, exitcode%)

'CALL ismover(1 ' st, 1 * sf, 0, 0, exitcode%)

'CALL ismover(o, -1 * sf, 0, 0, exitcode%)
'FOR x = 1 T0 3

' CALL ismover(-1 " sf, 0, 0, 0, exitcode%)
CALL ismover(O, -1 * $1.0, 0, exitcode%)
' CALL ismover(1 * sf, 0, 0, 0, exitcode%)

' CALL ismover(O, -1 * st, 0, 0, exitcode%)

'NEXT x

'CALL ismover(O, 12 * sf, 0, 0, exitcode%)
CALL ismover(-1 * sf, 6 * sf, 0, 0, exitcode%)
CALL ismover(0, 3 * sf, 0, 0, exitcode%)
CALL ismover(1 " sf, 7 ’ sf, 0, 0, exitcode%)
'CALL ismover(O, 3 * sf, 0, 0, exitcode%)
'CALL ismover(1 * sf, 0, 0, 0. exitcode%)
'CALL ismover(O, 5 * sf, 0, 0, exitcode%)
'CALL ismover(-1 * sf, 0, 0, 0, exitcode%)
‘CALL ismover(O, 7 * sf, 0, 0, exitcode%)
'CALL ismover(-1 " st, 0, 0,0, exitcode%)

'to K old

'toK

'to L old

‘toL

'to M old

'to M

207

'CALL ismover(o, -1 * sf, 0, 0, exitcode%)
'CALL ismover(1 " st, 0, 0, 0, exitcode%)
'CALLismover(-1 * sf, 1 " st, 0, 0, exitcode%)
'CALL ismover(o, 2 * st, 0, 0, exitcode%)
'CALL ismover(-1 ' sf, 0, 0, 0, exitcode%)
'CALL ismover(O, 2 " sf, 0, 0, exitcode%)
'CALL ismover(-1 ‘ sf, 0, 0, 0, exitcode%)
'CALL ismover(O, 1 " st, 0, 0, exitcode%)
'CALL ismover(1 * sf, 0, 0, 0, exitcode%)
'CALL ismover(0, 2 " st, 0, 0, exitcode%)
'CALL ismover(-1 ' sf, 0. 0, 0, exitcode%)
'CALL ismover(O, 1 " st, 0, 0, exitcode%)
'CALL ismover(-2 * st, 0, 0, 0, exitcode%)
'CALL ismover(O, 1 " sf, 0, 0, exitcode%)
'CALL ismover(-1 " st, 0, 0, 0, exitcode%)
'CALL ismover(O, 1 " st, 0, 0, exitcode%)
'CALL ismover(-2 * st, 0, 0, 0, exitcode%) 'to (1,81) old
CALL ismover(1 * st, 4 " sf, 0, 0, exitcode%)
CALL ismover(o, 3 ' st, 0, 0, exitcode%)
CALL ismover(-1 " sf, 7 " st, 0, 0, exitcode%)
CALL ismover(-1 * sf, 3 * st, 0, 0, exitcode%)
CALL ismover(-1 * sf, 2 ' sf, 0, 0, exitcode%)
CALL ismover(-2 ' sf, 3 " sf, 0, 0, exitcode%)
CALL ismover(-3 " sf, 2 * st, 0, 0, exitcode%)
CALL ismover(-3 * sf, 1 ' st, 0, 0, exitcode%) 'to (1,81)
CALL closeshutter(delay°/e)
PRINT “plume done'

END SUB

SUB support (sf, delay°/e)
'support 1
CALL openshutter(delay%)
'CALL ismover(0, -3 " sf, 0, 0, exitcode%)
'CALL ismover(-1 * st, 0, 0, 0, exitcode%)
'CALL ismover(o, -5 " sf, 0. 0, exitcode%)
'CALL ismover(1 " sl, -1 ‘ sf, 0, 0, exitcode%)
'CALL ismover(o, -1 * sf, 0, 0. exitcode%)
'CALL ismover(6 * sf, 0, 0, 0, exitcode%)
'CALL ismover(0, 1 " sf, 0, 0, exitcode%)
'CALL ismover(2 * sf, 0, 0, 0, exitcode%)
'CALL ismover(O, 1 * sf, 0, 0, exitcode%)
'CALL ismover(-4 * sf, 0, 0, 0, exitcode%)
' FOR x = 1 TO 3
' CALL ismover(o, 1 ‘ sf, 0, 0, exitcode%)
' CALL ismover(-1 ‘ st, 0, 0, 0, exitcode%)
'NEXT x
'CALL ismover(o, 2 * st, 0, 0, exitcode%)
'CALL ismover(-1 " sf, 0, 0, 0, exitcode%) '10 (14,50) old
CALL ismover(-1 * sf, -5 * st, 0, 0, exitcode%)
CALL ismover(O, -1 ‘ sf, 0, 0, exitcode%)
CALL ismover(1 " st, -4 " sf, 0, 0, exitcode%)
CALL ismover(8 "’ sf. 1 * sf, 0, 0, exitcode%)
CALL ismover(o, 1 ‘ st, 0,0, exitcode%)
CALL ismover(-3 " sf, 0, 0, 0, exitcode%)
CALL ismover(2 * sl, 1 ‘ st, 0, 0, exitcode%)
CALL ismover(4 " sf, 1 " st, 0, 0, exitcode%)

208

CALL ismover(-2 " st, 4 ' sf, 0, 0, exitcode%)
CALL ismover(O, 2 * sf, 0, 0, exitcode%)
CALL closeshutter(20000)
CALL ismover(o, -3 * sf, 0, 0, exitcode%)‘to original and pt. (14,50)
CALL ismover(10 " sf, -8 * sf, 0, 0, exitcode%)
CALL ismover(O, -1 "‘ sf, 0, 0, exitcode%) 'moved from below
'support 2
CALL openshutter(delay%)
'CALL ismover(o, -1 ' s1, 0, 0, exitcode%) 'moved to above
CALL ismover(-9 ‘ sf, -1 * sf, 0, 0, exitcode%)
CALL ismover(1 " sf, -3 ‘ sf, 0, 0, exitcode%)
CALL ismover(8 ' sf, 4 * sf, 0, 0, exitcode%)
CALL closeshutter(20000)
CALL ismover(3 " sf, -3 ' sl, 0, 0, exitcode%)
'support 3
CALL openshutter(delay%)
CALL ismover(-2 * st, 0, 0, 0, exitcode%)
CALL ismover(-7 * st, -3 * st, 0, 0, exitcode%)
CALL ismover(0, -1 ‘ st, 0, 0, exitcode%)
CALL ismover(2 * sf, -2 * st, 0, 0, exitcode%)
CALL ismover(1 " sf, 0, 0, 0, exitcode%)
CALL ismover(5 " sf, 5 " sf, 0, 0, exitcode%)
CALL ismover(1 ‘ sf, 0, 0, 0, exitcode%)
CALL ismover(o, 1 " sf, 0, 0, exitcode%)
CALL closeshutter(20000)
CALL ismover(2 " sf, -2 " sf, 0, 0, exitcode%)
'support 4
CALL openshutter(delay%)
CALL ismover(-4 " sf, -4 ’ st, 0. 0, exitcode%)
CALL ismover(-3 ' st, -2 * sf, 0, 0, exitcode%)
CALL ismover(-1 ' st, 0, 0, 0, exitcode%)
CALL ismover(o, -1 * st, 0, 0, exitcode%)
CALL ismover(2 * st, -2 * st, 0, 0, exitcode%)
CALL ismover(1 " sf, 0, 0, 0, exitcode%)
CALL ismover(2 * sf, 3 ' sf, 0, 0, exitcode%)
CALL ismover(4 " st. 4 ' sf, 0, 0, exitcode%)
CALL ismover(-1 * sf, 2 ‘ sf, 0, 0, exitcode%)
CALL closeshutter(20000)
CALL ismover(4 " sf, -3 ' st, 0, 0, exitcode%)
CALL ismover(-1 * st, 0, 0, 0, exitcode%) 'tor smoothness
'support 5
CALL openshutter(delay%)
'CALL ismover(-2 * sf, 0, 0, 0, exitcode%)
CALL ismover(-1 * sf, 0, 0, 0, exitcode%) 'replaces last to smooth
CALL ismover(-5 * sf, -7 * sf, 0, 0, exitcode%)
CALL ismover(O, -1 ‘ sf, 0, 0, exitcode%)
CALL ismover(2 " sf, -2 " st, 0, 0, exitcode%)
CALL ismover(5 ’ sf, 8 ' st, 0, 0, exitcode%)
'CALL ismover(O, 2 * st, 0, 0, exitcode%)
CALL ismover(O, 1 * st, 0, 0, exitcode%) ‘these two replace previous
CALL ismover(-1 ‘ sf, 1 " sf, 0, 0, exitcode%) 'line - to smooth
CALL closeshutter(20000)
CALL ismover(2 * sf, -2 " st, 0, 0, exitcode%)
'support 6
CALL openshutter(delay%)
CALL ismover(-3 * sf, -9 * st, 0, 0, exitcode%)

209

'CALL ismover(-1 " s1. 0, 0, 0, exitcode%)
'CALL ismover(3 " st, -1 " sf, 0, 0, exitcode%)
CALL ismover(2 ‘ st, -1 " sf, 0, 0, exitcode%) 'replaces last two
CALL ismover(1 ' sf, 1 * $1.0, 0, exitcode%)
CALL ismover(2 ' sf, 8 " st, 0, 0, exitcode%)
'CALL ismover(0, 1 * st, 0, 0, exitcode%)
'CALL ismover(-2 * 31,0, 0, 0, exitcode%)
CALL ismover(-2 * st, 1 * sf, 0, 0, exitcode%) 'combines last two
CALL closeshutter(20000)
CALL ismover(6 * s1, -1 " sf, 0, 0, exitcode%)
'support 7
CALL openshutter(delay%)
CALL ismover(-1 * sf, 0, 0, 0, exitcode%)
'CALL ismover(-1 * 51.-1 " sf, 0, 0, exitcode%)
CALL ismover(4 " st, 0, 0, 0, exitcode%) 'previous line as two
CALL ismover(0, -1 * sf, 0, 0, exitcode%) 'lines instead of one
CALL ismover(-2 ' sf, -8 * sf, 0, 0, exitcode%)
CALL ismover(0, -1 ' sf, 0, 0, exitcode%)
CALL ismover(4 " sf, -1 * sf, 0, 0, exitcode%)
CALL ismover(0, 11 " sf, 0, 0, exitcode%)
CALL closeshutter(20000)
CALL ismover(3 * sf, 0, 0, 0, exitcode%)
'support 8
CALL openshutter(delay%)
CALL ismover(0, -11 ' st, 0, 0, exitcode%)
CALL ismover(7 ‘ sf, 0, 0, 0, exitcode%)
CALL ismover(4 " st, 1 * st, 0, 0, exitcode%)
CALL ismover(2 " sf, 0. 0, 0, exitcode%)
CALL ismover(-2 * st, 0, 0,0, exitcode%)
CALL ismover(-3 " sf, 1 * st, 0, 0, exitcode%)
CALL ismover(4 " st, 2 " sf, 0, 0, exitcode%)
CALL ismover(-1 * sf, 1 " sf, 0, 0, exitcode%)
CALL ismover(4 * sf, 2 ‘ sf, 0, 0, exitcode%)
CALL ismover(-2 " sf, 4 * sf, 0, 0, exitcode%) 'to (44.30)
CALL closeshutter(20000)
PRINT 'supports done'
END SUB

210

DECLARE SUB checkexit (exitcode%)

DECLARE SUB drawM (sf!) 'draws the letter M by moving surface
DECLARE SUB spaceletter (sf!) 'switches from M to S or S to U
DECLARE SUB drawS (sf!) 'draws the letter S by moving surface
DECLARE SUB drawU (sf!) 'draws the letter U by moving surface
'SINCLUDE: 'lS_BC.BI' 'enables instep library

'SINCLUDE: 'QB.BI'

'Main Body
a = 1
b = 1
WHILE a = 1
CALL ischeckcard(592, checkcode%) 'checks to see if card is present
IF checkcode% = 0 THEN
PRINT 'Card not found."
INPUT 'Do you wish to try again (1 =yes,0=no)"; b
ELSE a = 0
END IF
lFb=0THENa=0
WEND
IF b = 0 THEN END

'INPUT 'Do you wish to end on movement errors (1=yes, 0=no)? ', eoe%

'I may eventually put in this option, but eoe% must then be passed to each
'Ietter‘s subroutine.

CALL issetcardtype(1) 'sets the card type to QuickPhase half stepping mode
CALL issetcplane(1, 2) 'defines x and y axes for drawing arcs

sf = 50 'sets size factor

CALL ispowerinit(10) 'sets power level (to 20%)

speed% is speed in steps per second

'delay% = 2000000 / speed% 'calculates delay between steps for speed setting
CALL issetspeed(32767) 'sets stepper motor speed to speed steps per second
CALL issetmode(0) 'sets motion stage to relative mode

PRINT “Starting Movement"

CALL drawM(sf)

CALL spaceletter(sf)

CALL drawS(sf)

CALL spaceletter(sf)

CALL drawU (sf)

INPUT 'Retum to Starting Position (1=yes, 0=no)? ', origin

CALL issetspeed(20000) 'sets speed to 100 steps/sec

IF origin = 1 THEN CALL ismover(-26 * sf, 0, 0, 0, exitcode%)

END

SUB checkexit (exitcode%) 'Add parameter eoe% for End On Error option
IF NOT exitcode% = 0 THEN
SELECT CASE exitcode%
CASE exitcode°/o = 1 TO 2
PRINT “Limit Switch Encountered - M1 "
CASE exitcode% = 3 T0 4
PRINT “Limit Switch Encountered - M2“
CASE exitcode°/e = 5 TO 6
PRINT "Limit Switch Encountered - M3“
CASE exitcode°/e = 7 TO 8

211

PRINT “Limit Switch Encountered - M4“
CASE exitcode% = 32
PRINT “Encoder Error on M1“
CASE exitcode% = 33
PRINT “Encoder Error on M2“
CASE exitcode% = 34
PRINT “Encoder Error on M3“
CASE exitcode% = 35
PRINT “Encoder Error on M4“
CASE exitcode% = 51
PRINT “Shield Open“
CASE exitcode% = 129
PRINT “Keyboard Abort (ESC)“
CASE exitcode% = 185
PRINT “Keyboard Pause (spacebar)“
CASE ELSE
PRINT “Move Unsuccessful - Reason Unknown“
END SELECT
'lF eoe% = 1 THEN END
END IF
END SUB

SUB drawM (sf)
CALL issetspeed(2000000 / 1000) 'sets speed to 1000 steps/sec
CALL ismover(0, 0, -365, 0, exitcode%) 'unblocks laser
lF exitcode% THEN CALL checkexit(exitcode%) 'error check
CALL issetspeed(32767) 'retums to writing speed
CALL ismover(0, -8 “ sf, 0, 0, exitcode%) ’first leg of M
lF exitcode THEN CALL checkexit(exitcode%) 'error check
CALL ismover(3 * sf, 4 “ sf, 0, 0, exitcode%) 'down to middle of M
IF exitcode THEN CALL checkexit(exitcode%) 'error check
CALL ismover(3 “ sf, -4 “ sf, 0, 0, exitcode%) 'up from middle of M
IF exitcode THEN CALL checkexit(exitcode%) 'error check
CALL ismover(0, 8 “ sf, 0, 0, exitcode%) 'last leg of M
IF exitcode THEN CALL checkexit(exitcode%) 'error check
CALL issetspeed(2000) 'sets speed to 1000 steps/sec
CALL ismover(0, 0, 365, 0, exitcode%) 'blocks laser

IF exitcode THEN CALL checkexit(exitcode%) 'error check
END SUB

SUB draws (sf)
CALL issetspeed(2000) 'sets speed to 1000 steps/sec
CALL ismover(0, 0, -365, 0, exitcode%) 'unblocks laser
IF exitcode% THEN CALL checkexit(exitcode%) 'error check
CALL issetspeed(32767) 'resets to writing speed
CALL isarc(2 ' sf, 0, 2 “ sf, -2 “ sf, 1, exitcode%) 'bottom of S
IF exitcode% THEN CALL checkexit(exitcode%) 'error check
CALL isarc(0, -2 “ sf, 2 “ sf, -2 “ sf, -1, exitcode%) 'top of S
IF exitcode% THEN CALL checkexit(exitcode%) 'error check
CALL issetspeed(2000) 'sets speed to 1000 steps/sec
CALL ismover(0, 0, 365, 0, exitcode%) 'blocks laser

IF exitcode% THEN CALL checkexit(exitcode%) 'error check
END SUB

SUB drawU (sf)
CALL issetspeed(2000) 'sets speed to 1000 steps/sec

212

CALL ismover(0, 0, -365, 0, exitcode%) 'unblocks laser

IF exitcode% THEN CALL checkexit(exitcode%) 'error check
CALL issetspeed(32767) 'resets to writing speed

CALL ismover(0, 6 “ sf, 0, 0, exitcode%) 'Ieft line of U

IF exitcode% THEN CALL checkexit(exitcode%) 'error check
CALL isarc(2 * sf, 0, 4 “ sf, 0, 1, exitcode%) 'bottom of U

lF exitcode% THEN CALL checkexit(exitcode%) 'error check

CALL ismover(0, -6 “ sf, 0, 0, exitcode%) 'right line of U
IF exitcode% THEN CALL checkexit(exitcode°/o) 'error check
CALL ismover(0, 6 “ sf, 0, 0, exitcode%) 'positioning step

lF exitcode% THEN CALL checkexit(exitcode%) 'error check
CALL isarc(2 “ sf, 0, 2 * sf, 2 “ sf, 1, exitcode%) 'tail of U

IF exitcode% THEN CALL checkexit(exitcode%) 'error check
CALL issetspeed(2000) 'sets speed to shutter speed
CALL ismover(0, 0, 365, 0, exitcode%) 'blocks laser

IF exitcode% THEN CALL checkexit(exitcode%) 'error check
END SUB

SUB spaceletter (sf)
CALL issetspeed(20000) 'sets speed to 100 steps/sec
CALL ismover(5 * sf, -2 * sf, 0, 0, exitcode%) 'move to next letter
IF exitcode% THEN checkexit (exitcode%) 'error check
END SUB

213

APPENDIX C

Sampare program for the motion stage control, composed by the QuickBasic, Microsoft.

0 Three isolated-cell pattern in Figure 93

DECLARE SUB checkexit (exitcode%)
DECLARE SUB outerblock (sf!)

DECLARE SUB innerblocks (sf!)

'$|NCLUDE: 'lS_BC.Bl' 'enables instep library
'$lNCLUDE: 'QB.BI'

'Main Body
CALL ischeckcard(592, checkcode°/e) 'checks to see if card is present
lF checkcode% = 0 THEN

PRINT “Card not found.“

END
END IF
'INPUT “Do you wish to end on movement errors (1 =yes, 0=no)? “, eoe%
'I may eventually put in this option, but eoe% must then be passed to each
'Ietter's subroutine.
CALL issetcardtype(1) 'sets the card type to QuickPhase half stepping mode
CALL issetcplane(1, 2) 'defines x and y axes for drawing arcs

sf = 50 'sets size factor
CALL ispowerinit(10) 'sets power level (to 20%)
speed% = 50 'speed in steps per second

'delay% = 2000000 I speed% 'calculates delay between steps for speed setting
CALL issetspeed(32767) 'sets stepper motor speed to speed steps per second
CALL issetmode(0) 'sets motion stage to relative mode

PRINT “Starting Movement“

CALL outerblock(sf)

CALL innerblocks(sf)

PRINT “Test Pattern Drawn.“

PRINT “Returning to original position“

CALL issetspeed(20000) 'sets to spacing speed

CALL ismover(-18 “ sf, 2 “ sf, 0, 0, exitcode%)‘retums to original position

END

SUB checkexit (exitcode%) 'Add parameter eoe% for End On Error option
IF NOT exitcode% = 0 THEN
SELECT CASE exitcode%

CASE exitcode% = 1 TO 2

PRINT “Limit Switch Encountered - M1“
CASE exitcode% = 3 TO 4

PRINT “Limit Switch Encountered - M2“
CASE exitcode% = 5 TO 6

PRINT “Limit Switch Encountered - M3“
CASE exitcode% = 7 TO 8

PRINT “Limit Switch Encountered - M4“
CASE exitcode% = 32

PRINT “Encoder Error on M1“

214

CASE exitcode% = 33
PRINT “Encoder Error on M2“
CASE exitcode% = 34
PRINT “Encoder Error on M3“
CASE exitcode% = 35
PRINT “Encoder Error on M4“
CASE exitcode% = 51
PRINT “Shield Open“
CASE exitcode% = 129
PRINT “Keyboard Abort (ESC)“
CASE exitcode% = 185
PRINT “Keyboard Pause (spacebar)“
CASE ELSE
PRINT “Move Unsuccessful - Reason Unknown“
END SELECT
'IF eoe% = 1 THEN END
END IF
END SUB

SUB innerblocks (sf)
CALL issetspeed(20000) 'set speed to spacing speed
CALL ismover(6 * sf, 0, 0, 0, exitcode%)
CALL issetspeed(2000) 'sets to shutter speed
CALL ismover(0, 0, -365, 0, exitcode%)bpens shutter
CALL issetspeed(32767) 'sets speed to drawing speed
CALL ismover(0, -9 “ sf, 0, 0, exitcode%)
CALL ismover(1 “ sf, 0. 0, 0, exitcode%)
CALL ismover(0, 10 “ sf, 0, 0, exitcode%)
CALL ismover(1 “ sf. 0, 0, 0, exitcode%)
CALL ismover(0, -9 “ sf, 0. 0, exitcode%)
CALL issetspeed(2000) 'set to shutter speed
CALL ismover(0, 0, 365, 0, exitcode%) 'closes shutter
CALL issetspeed(20000) 'set to spacing speed
CALL ismover(6 “ sf, 0, 0, 0, exitcode%)
CALL issetspeed(2000) 'set to shutter speed
CALL ismover(0, 0, -365, 0, exitcode%) ’opens shutter
CALL issetspeed(32767) 'set to drawing speed
CALL ismover(0, 9 “ sf, 0, 0, exitcode%)
CALL ismover(1 “ sf, 0, 0, 0, exitcode%)
CALL ismover(0, -10 “ sf, 0, 0, exitcode%)
CALL ismover(1 “ sf, 0, 0, 0, exitcode%)
CALL ismover(0, 9 “ sf, 0, 0, exitcode%)
'inner blocks done
CALL issetspeed(2000) 'set to shutter speed

CALL ismover(0, 0, 365, 0, exitcode%) 'closes shutter
END SUB

SUB outerblock (sf)
CALL issetspeed(2000) 'sets speed to 1000 steps/sec
CALL ismover(0, 0, -365, 0, exitcode%) 'opens shutter
CALL issetspeed(32767) 'sets speed to drawing speed
CALL ismover(0, -12 “ sf, 0, 0, exitcode%)
CALL ismover(26 “ sf, 0, 0, 0, exitcode%)
CALL ismover(0, 12 “ sf, 0, 0, exitcode%)
CALL ismover(-26 “ sf, 0, 0, 0, exitcode%)
'if we want to change the spot size or the size of the pattern,

215

'a for next loop will need to be included for this next part
CALL ismover(1 “ sf, -1 “ st, 0, 0, exitcode%)

CALL ismover(0, -10 “ sl, 0, 0, exitcode%)

CALL ismover(24 " sf, 0, 0, 0. exitcode%)

CALL ismover(0, 10 “ sf, 0, 0, exitcode%)

CALL ismover(-24 “ sf, 0. 0. 0, exitcode%)

CALL ismover(1 “ sf, -1 “ sf. 0, 0, exitcode%)

CALL ismover(0, -8 “ st, 0, 0, exitcode%)

CALL ismover(22 “ sf, 0, 0, 0, exitcode%)

CALL ismover(0, 8 “ sf, 0, 0, exitcode%)

CALL ismover(-22 “ sf, 0, 0, 0, exitcode%)

'outer block drawn

CALL issetspeed(2000) 'sets speed to shutter speed

CALL ismover(0, 0, 365, 0, exitcode%) 'closes shutter
END SUB

216

APPENDIX D

So are ro mm or the motion sta e control com osed b the uickBasic Microso .

- Patterned cut for the circular lens in Figure 94

DECLARE SUB checkexit (exitcode%)

DECLARE SUB drawO (sfl) 'draws the circle moving surface
'$INCLUDE: 'IS_BC.BI' 'enables instep library

'$INCLUDE: 'QB.BI'

'Main Body
a = 1
b = 1
WHILE a = 1
CALL ischeckcard(592, checkcode%) 'checks to see it card is present
IF checkcode°/o = 0 THEN
PRINT “Card not found.“
INPUT “Do you wish to try again (1 =yes,0=no)“; b
ELSE a = 0
END IF
IFb=0THENa=0
WEND
IF b = 0 THEN END
CALL issetcardtype(1) 'sets the card type to QuickPhase half stepping mode
CALL issetcplane(1. 2) 'defines x and y axes for drawing arcs
sf = 150 'sets size factor
CALL ispowerinit(10) 'sets power level (to 20°/o)
speed% is speed in steps per second
'delay% = 2000000 / speed% 'calculates delay between steps for speed setting
CALL issetspeed(32767) 'sets stepper motor speed to speed steps per second
CALL issetmode(0) 'sets motion stage to relative mode
PRINT “Starting Movement“

CALL issetspeed(2000000 / 1000) 'sets speed to 1000 steps/sec
CALL ismover(0, 0, -365, 0, exitcode%) 'unblocks laser
IF exitcode% THEN CALL checkexit(exitcode%) 'error check

CALL issetspeed(32767) 'retums to writing speed
INPUT “How many repetitions do you want?“, x
FOR N = 1 TO x
CALL drawO(sf)
NEXT N

CALL issetspeed(2000000/ 1000) 'sets speed to 1000 steps/sec
CALL ismover(0, 0, 365, 0, exitcode%) 'blocks laser
IF exitcode THEN CALL checkexit(exitcode%) 'error check

217

INPUT “Return to Starting Position (1 =yes, 0=no)? “, origin
CALL issetspeed(20000) 'sets speed to 100 steps/sec

IF origin = 1 THEN CALL ismover(0, 0, 0, 0, exitcode%)
END

SUB checkexit (exitcode%) 'Add parameter eoe% for End On Error option
IF NOT exitcode% = 0 THEN
SELECT CASE exitcode%
CASE exitcode% = 1 TO 2
PRINT “Limit Switch Encountered - M1“
CASE exitcode% = 3 TO 4
PRINT “Limit Switch Encountered - M2“
CASE exitcode% = 5 TO 6
PRINT “Limit Switch Encountered - M3“
CASE exitcode% = 7 TO 8
PRINT “Limit Switch Encountered - M4“
CASE exitcode% = 32
PRINT “Encoder Error on M1“
CASE exitcode% = 33
PRINT “Encoder Error on M2“
CASE exitcode% = 34
PRINT “Encoder Error on M3“
CASE exitcode% = 35
PRINT “Encoder Error on M4“
CASE exitcode% = 51
PRINT “Shield Open“
CASE exitcode% = 129
PRINT “Keyboard Abort (ESC)“
CASE exitcode% = 185
PRINT “Keyboard Pause (spacebar)“
CASE ELSE
PRINT “Move Unsuccessful - Reason Unknown“
END SELECT
'IF eoe% = 1 THEN END
END IF
END SUB

SUB drawO (sf!)
centerx& = -3 “ sf: centery& a 0 'select a start point
Xdest& = 0: Ydest& = 0 'full circle
dir°/o = 1 “clockwise rotation

CALL isarc(centerx&, centery&, Xdest&, Ydest&, dir%, exitcode%)
END SUB

218

APPENDIX E

Somme program for phi motion stage controlI composed by the QuickBasic, Microsoﬂ.

o Patterned cut for the square lens in Figure 95

DECLARE SUB checkexit (exitcode%)

DECLARE SUB drawSQ (sfl) 'draws the letter M by moving surface
'$INCLUDE: 'IS_BC.BI' 'enables instep library

'$INCLUDE: 'QB.BI'

'Main Body
a = 1
b = 1
WHILE a = 1
CALL ischeckcard(592, checkcode%) 'checks to see if card is present
IF checkcode% = 0 THEN
PRINT “Card not found.“
INPUT “Do you wish to try again (1=yes,0=no)"; b
ELSE a = 0
END IF
IFb=0THENa=0
WEND
IF b = 0 THEN END

'lNPUT “Do you wish to end on movement errors (1 =yes, 0=no)? “, eoe%

'I may eventually put in this option, but eoe% must then be passed to each
'letter‘s subroutine.

CALL issetcardtype(1) 'sets the card type to QuickPhase half stepping mode
CALL issetcplane(1, 2) 'defines x and y axes for drawing arcs

sf = 100 'sets size factor

CALL ispowerinit(10) 'sets power level (to 20%)

speed% is speed in steps per second

'delay% = 2000000 / speed% 'calculates delay between steps for speed setting
CALL issetspeed(32767) 'sets stepper motor speed to speed steps per second
CALL issetmode(0) 'sets motion stage to relative mode

PRINT “Starting Movement“

CALL drawSO(sf)

INPUT “Return to Starting Position (1=yes, 0=no)? “, origin
CALL issetspeed(20000) 'sets speed to 100 steps/sec

IF origin = 1 THEN CALL ismover(0, 0, 0, 0, exitcode%)
END

SUB checkexit (exitcode%) 'Add parameter eoe% for End On Error option
IF NOT exitcode% = 0 THEN
SELECT CASE exitcode%
CASE exitcode% = 1 TO 2
PRINT “Limit Switch Encountered - M1“
CASE exitcode% = 3 TO 4

219

PRINT “Limit Switch Encountered - M2“
CASE exitcode% = 5 TO 6
PRINT “Limit Switch Encountered - M3“
CASE exitcode% = 7 TO 8
PRINT “Limit Switch Encountered - M4“
CASE exitcode% = 32
PRINT “Encoder Error on M1“
CASE exitcode% = 33
PRINT “Encoder Error on M2“
CASE exitcode% = 34
PRINT “Encoder Error on M3“
CASE exitcode% = 35
PRINT “Encoder Error on M4“
CASE exitcode% = 51
PRINT “Shield Open“
CASE exitcode% = 129
PRINT “Keyboard Abort (ESC)“
CASE exitcode% = 185
PRINT “Keyboard Pause (spacebar)“
CASE ELSE
PRINT “Move Unsuccessful - Reason Unknown“
END SELECT
'IF eoe% = 1 THEN END
END IF
END SUB

SUB drawSQ (sf)
CALL issetspeed(2000000 I 1000) 'sets speed to 1000 steps/sec
CALL ismover(0, 0, -365, 0, exitcode%) 'unblocks laser
IF exitcode% THEN CALL checkexit(exitcode%) 'error check
CALL issetspeed(32767) 'retums to writing speed

CALL ismover(8 “ sf, 0, 0, 0, exitcode%) “first leg

IF exitcode THEN CALL checkexit(exitcode%) 'error check
CALL ismover(0, 8 “ sf, 0, 0, exitcode%) 'last leg

IF exitcode THEN CALL checkexit(exitcode%) 'error check
CALL ismover(-8 “ sf, 0, 0, 0, exitcode%) 'first leg

IF exitcode THEN CALL checkexit(exitcode%) 'error check
CALL Ismover(0, -8 “ sf, 0, 0. exitcode%) 'last leg

IF exitcode THEN CALL checkexit(exitcode%) 'error check

CALL issetspeed(2000) 'sets speed to 1000 steps/sec
CALL ismover(0, 0, 365. 0, exitcode%) “blocks laser

IF exitcode THEN CALL checkexit(exitcode%) 'error check
END SUB

220

APPENDIX F

Software program [or the motion stage controlI composed by the QuickBasic, Microsoft.

 

- Patterning for the circular contour track in Figure 96

DECLARE SUB draw1 (sfl)

DECLARE SUB checkexit (exitcode%)

DECLARE SUB drawO (sfl) 'draws the circle moving surface
'$lNCLUDE: 'IS_BC.BI' 'enables instep library

'$lNCLUDE: 'QB.BI'

“Main Body
a = 1
b = 1
WHILE a = 1
CALL ischeckcard(592, checkcode%) 'checks to see if card is present
IF checkcode% = 0 THEN
PRINT “Card not found.“
INPUT “Do you wish to try again (1=yes,0=no)“; b
ELSE a = 0
END IF
IFb=0THENa=0
WEND
IF b = 0 THEN END
CALL issetcardtype(1) 'sets the card type to QuickPhase half stepping mode
CALL issetcplane(1, 2) 'defines x and y axes for drawing arcs
sf = 150 'sets size factor
CALL ispowerinit(10) 'sets power level (to 20%)
speed% is speed in steps per second
'delay% = 2000000 / speed% 'calculates delay between steps for speed setting
CALL issetspeed(32767) 'sets stepper motor speed to speed steps per second
CALL issetmode(0) 'sets motion stage to relative mode
PRINT “Starting Movement“

CALL issetspeed(2000000 / 1000) 'sets speed to 1000 steps/sec
CALL ismover(0, 0, -365, 0. exitcode%) 'unblocks laser
IF exitcode% THEN CALL checkexit(exitcode%) 'error check

CALL issetspeed(32767) 'retums to writing speed
INPUT “How many repetitions do you want?“, x
FOR N = 1 TO x
CALL draw1 (sf)
NEXT N

CALL issetspeed(2000000 / 1000) 'sets speed to 1000 steps/sec
CALL ismover(0, 0, 365, 0, exitcode%) 'blocks laser
IF exitcode THEN CALL checkexit(exitcode%) 'error check

221

INPUT “Return to Starting Position (1=yes, 0=no)? “, origin
CALL issetspeed(20000) 'sets speed to 100 steps/sec

IF origin = 1 THEN CALL ismover(0, 0. 0, 0, exitcode%)
END

SUB checkexit (exitcode%) 'Add parameter eoe% for End On Error option
IF NOT exitcode% = 0 THEN
SELECT CASE exitcode%
CASE exitcode% = 1 TO 2
PRINT “Limit Switch Encountered - M1“
CASE exitcode% = 3 TO 4
PRINT “Limit Switch Encountered - M2“
CASE exitcode% = 5 TO 6
PRINT “Limit Switch Encountered - M3“
CASE exitcode% = 7 TO 8
PRINT “Limit Switch Encountered - M4“
CASE exitcode% = 32
PRINT “Encoder Error on M1“
CASE exitcode% = 33
PRINT “Encoder Error on M2“
CASE exitcode% = 34
PRINT “Encoder Error on M3“
CASE exitcode% = 35
PRINT “Encoder Error on M4“
CASE exitcode% = 51
PRINT “Shield Open“
CASE exitcode% = 129
PRINT “Keyboard Abort (ESC)“
CASE exitcode% = 185
PRINT “Keyboard Pause (spacebar)“

CASE ELSE
PRINT “Move Unsuccessful - Reason Unknown“
END SELECT
'IF eoe% = 1 THEN END
END IF
END SUB

SUB draw1 (sfl)
CALL issetspeed(32767) 'retums to writing speed
CALL ismover(0, -10.7 “ sf, 0, 0, exitcode%) 'first leg
IF exitcode THEN CALL checkexit(exitcode%) 'error check
END SUB

BIBLIOGRAPHY

222

10.

223

BIBLIOGRAPHY

H. Liu and D.S. dandy, Diamond Chemical Vapor Deposition: Nucleation and
Early Growth Stages. Park Ridge, NJ: Noyes Publications, 1995.

J .E. Butler and R.L. Woodin, “Thin Film Diamond Growth Mechanisms,” Phil.
Trans. R. Soc. Land. A, vol. 342, pp. 209-224, 1993.

RE Davis, Diamond Films and Coatings. Park Ridge, NJ: Noyes Publications,
1992.

A. Lettington and J .W. Steeds, Thin Film Diamond. New York, NY: Chapman &
Hall, 1994.

KB Spear, Synthetic Diamond: Emerging CVD Science and Technology. New
York, NY: Willy-Interscience Publication, 1994.

P.K. Bachmann, D. Leers, and H. Lydtin, “Toward a General Concept of General

Diamond Chemical Vapor Deposition,” Diamond and Related Materials, vol. 1,
pp. 1-12, 1992.

P.W. Green, R.R.A. Syms, and EM. Yeatman, “Demonstration of Three-
Dimensional Microstructure Self-Assembly,” Journal of Microelectromechanical
Systems, vol. 4, no. 4, pp. 170-176, 1995.

Y. Fukuta, D. Collard, T. Akiyama, E.H. Yang, and H. Fujita, “Microactuated
Self-Assembling of 3D Polysilicon Structures with Reshaping Technology,” The
10th Annual International Workshop on Micro Electro Mechanical Systems, pp.
477-481, Nagoya, Japan: IEEE, 1997.

H. Miyajima and M. Mehregany, “High-Aspect-Ratio Photolithography for
MEMS Applications,” Journal of Microelectromechanical Systems, vol. 4, no. 4,
pp. 220-229, 1995.

CR. Friedrich and M.J. Vasile, “Development of the Micromilling Process for
High-Aspect-Ratio Microstructures,” Journal of Microelectromechanical
Systems, vol. 5, no. 1, pp. 33-38, 1996.

ll.

12.

13.

14.

15.

16.

17.

18.

19.

224

GB. Wolbold, C.L. Tessler, and BL. Tudryn, “Application of Excimer Lasers in
Electronic Packaging and Manufacturing,” Lambda Physik: Industrial Repot, no.
10, pp. 1-6, May, 1996.

RS. Patel, T.F. Redmond, C. Tessler, D. Tudryn, and D. Pulaki, “Via Production
Beneﬁts from Excimer-Laser Tools,” Laser Focus World, vol. 32, no. 1, pp. 71-
75, 1996.

U. Brinkmann and S. Ishizaka, “Laser LIGA - Excimer Laser Micro-Structuring
and Replication,” Lambda Physik: Highlights, no. 45, pp. 1-3, August 1994.

V.N. Tokarev, J .I.B. Wilson, M.G. Jubber, P. John, and D.K. Milne, “Modeling of
Self-Lirniting Laser Ablation of Rough Surfaces: Application to the Polishing of
Diamond Films,” Diamond and Related Materials, vol. 4, pp. 169-176, 1995.

A. Boudina, E. Fitzer, G. Wahl, and H. Esrom, “Improvement in IR Properties of
Chemically Vapor-Deposited Diamond Films by Smoothing with KrF Excimer
Radiation,” Diamond and Related Materials, vol. 2, pp. 678-682, 1993.

C. Johnston, P.R. Chalker, I.M. Buckley-Golder, P.J. Marsden, and SW.
Williams, “Diamond Device Delineation via Excimer Laser Patterning,” Diamond
and Related Materials, vol. 2, pp. 829-834, 1993.

S.M. Pimenov, A.A. Smolin, V.G. Ralchenko, V.I. Konov, S.V. Likhanski, I.A.
Veselovski, G.A. Sokolina, S.V. Bantsekov, and B.V. Spitsyn, “UV Laser
Processing of Diamond Films: Effects of Irradiation Conditions on the Properties
of Laser-Treated Diamond Film Surfaces,” Diamond Related Materials, vol. 2,
pp. 291-297, 1993.

V.G. Ralchenko, S.M. Pimenov, T.V. Kononenko, K.G. Korotoushenko, A.A.
Smolin, E.D. Obraztsova, and V.I. Konov, “Processing of CVD Diamond with
UV and Green Lasers,” Application of Diamond Films and Related Materials:
Third International Conference, (A. Feldman, Y. Tzeng, W.A. Yarbrough, M.
Yoshikawa, and M. Murakawa, Eds.), pp. 225-232, Gaithersburg, MD: National
Institute of Standard and Technology, 1995.

T. Chein, C. Cutshaw, C. Tanger, and Y. Tzeng, “Polishing of Thick CVD
Diamond by an Excimer Laser and a Cast Iron Wheel,” Application of Diamond
Films and Related Materials: Third International Conference, (A. Feldman, Y.
Tzeng, W.A. Yarbrough, M. Yoshikawa, and M. Murakawa, Eds.), pp. 257-260,
Gaithersburg, MD: National Institute of Standard and Technology, 1995.

20.

21.

22.

23.

24.

25.

26.

27.

225

P. Tosin, W. Liithy, and HP. Weber, “Laser Polishing of Diamond Films,”
Application of Diamond Films and Related Materials: Third International
Conference, (A. Feldman, Y. Tzeng, W.A. Yarbrough, M. Yoshikawa, and M.
Murakawa, Eds.), pp. 271-274, Gaithersburg, MD: National Institute of Standard
and Technology, 1995.

MD. Shirk, P.A. Molian, and AP. Malshe, “Ultrashort Pulsed Laser Ablation of
Diamond,” Journal of Laser Applications, vol. 10, no. 2, pp. 64-70, 1998.

M.A. Molian, R. Windholz, A.P. Malshe, G.J. Salamo, H.A. Naseem, W.D.
Brown, and U. Stamm, “Femtosecond Laser Processing of CVD-Diamond,”
Proceedings of the Second International Conference on Beam Processing of
Advanced Materials, (J. Singh, S.M. Copley, and J. Mazumder, Eds.), pp. 275-
278, Cleveland, Ohio: ASM International, 1995.

P.A. Molian, R. Windholz, A.P. Malshe, S. Jamil, and W.D. Brown,
“Femtosecond Laser-Diamond Interactions for Laser Machining Applications,”
Proceedings of the Second International Conference on Beam Processing of
Advanced Materials, (J. Singh, S.M. Copley, and J. Mazumder, Eds.), pp. 199-
206, Cleveland, Ohio: ASM International, 1995.

AP. Malshe, T.A. Railkar, A.M. Ozkan, P.A. Molian, A. Muyshondt, and W.D.
Brown, “Femtosecond Lasers: A Next Generation Tool for Processing of
Semiconductors and Metals,” The Third Paciﬁc Rim International Conference on
Advanced Materials and Processing, (M.A. Imam, R. DeNale, S. Hanada, Z.

Ziong, and D.N. Lee, Eds.), pp. 2195-2201, Honolulu, HA: The Minerals, Metals
& Materials Society, 1998.

RE. Dyer and R. Srinivasan, “Nanosecond Photoacoustic Studies on Ultraviolet

Laser Ablation of Organic Polymers,” Applied Physics Letters, vol. 48, pp. 445-
447, 1986.

U. Brinkmann, “Ultrafast Imaging of UV-Photon Ablation,” Lambda Physik:
Highlights, no. 21, pp. 1-4, February, 1994.

R. Srinivasan, B. Braren, K.G. Casey, and M. Yeh, “Ultrafast Imaging of
Ultraviolet Laser Ablation and Etching of Polymethylmethacrylate,” Applied
Physics Letters, vol. 26, pp. 2790-2791, 1989.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

40.

226

R. Srinivasan, K.G. Casey, B. Braren, and M. Yeh, “The Signiﬁcance of a
Fluence Thereshold for Ultraviolet Laser Ablation and Etching of Polymers,”
Journal of Applied Physics, vol. 67, pp. 1604-1606, 1990.

W.T. Silfvast, Laser Fundamentals. New York, NY: Cambridge University Press,
1996.

BA. Lengyel, Introduction to Laser Physics. New York, NY: John Wiley & Sons,
1967.

J .T. Luxon, D.E. Parker, and PD. Plotkowski, Lasers in Manufacturing. New
York, NY: IFS, 1987.

J. Wilson and J.F.B. Hawkes, Lasers: Principles and Applications. Hertfordshire,
UK: Prentice Hall, 1987.

K. Chang, Handbook of Microwave and Optical Components: Optical
Components, vol. 3. New York, NY: John Willey & Sons, 1990.

L. Allen and D.G.C. Jones, Principles of Gas Lasers. New York, NY: Plenum
Press, 1967.

M.J. Beesley, Lasers and Their Applications. New York, NY: Barnes & Noble,
1971.

J .F. Ready, Industrial Applications of Lasers. New York, NY: Academic Press,
1978.

GE. Wolbold, C.L. Tessler, and DJ. Tudryn, “Application of Excimer Lasers in
Electronic Packaging and Manufacturing,” Lambda Physik: Industrial Report, no.
10, PP. 1-6, 1996.

N. Bloembergen, Laser-Material Interactions; Fundamentals and Applications.
College Park, MD: American Institute of Physics, 1994.

U. Brackmann, Laser Dyes. Gottingen, Germany: Lambda Physik, 1992.

H. Rieck, Semiconductor Lasers. London, UK: MacDonald, 1970.

41.

42.

43.

45.

46.

47.

48.

49.

50.

227

J .E. Field, The Properties of Diamond. New York, NY: Academic, 1979.

S. Bohr, R. Haubner, and B. Lux, “Inﬂuence of Nitrogen Additions on Hot-
Filament Chemical Vapor Deposition of Diamond,” Applied Physics Letters, vol.
68, no. 8, pp. 1075-1077, 1996.

S. Khatami, “Controlled Synthesis of Diamond Films Using a Microwave
Discharge (Non—equilibrium Plasma),” Doctoral Dissertation, Dept. of Electrical
and Computer Engineering, Michigan State University, East Lansing, 1997.

K.P. Kuo, “Microwave Assisted Plasma CVD of Diamond Films Using Thermal-
Like Plasma Discharge,” Doctoral Dissertation, Dept. of Electrical and Computer
Engineering, Michigan State University, East Lansing, 1997.

C. Wild, R. Kohl, N. Herres, W. Muller-Sebert, and P. Koidl, “Oriented CVD
Diamond Films: Twin Formation, Structure and Morphology,” Diamond and
Related Materials, vol. 3, pp. 373-381, 1994.

CC. Battaile, D.J. Srolovitz, and J .E. Buttler, “Morphologies of Diamond Films
from Atomic-Scale Simulations of Chemical Vapor Deposition,” Diamond and
Related Materials, vol. 6, pp. 1198-1206, 1997.

F. Fuchs, C. Wild, K. Schwarz, W. Miiller-Sebert, and P. Koidl, “Hydrogen
Induced Vibrational and Electronic Transitions in Cmical Vapor Deposited

Diamond, Identiﬁed by Isotopic Substitution,” Applied Physics Letters, vol. 66,
no. 2, pp. 177-179, 1995.

R. Locher, C. Wild, N. Herres, D. Behr, and P. Koidl, “Nitrogen Stabilized (100)
Texture in Chemical Vapor Deposited Diamond Films,” Applied Physics Letters,
vol. 65, no. 1, pp. 34-36, 1994.

W. Mﬁller-Sebert, E. deer, F. Fuchs, C. Wild, and P. Koidl, “Nitrogen Induced
Increase of Growth Rate in Chemical Vapor Deposition of Diamond,” Applied
Physics Letters, vol. 68, no. 6, pp. 759-760, 1996.

R. Samlenski, C. Hang, and R. Brenn, “Incorporation of Nitrogen in Chemical

Vapor Deposition Diamond,” Applied Physics Letters, vol. 67, no. 19, pp. 2798-
2800, 1995.

51.

52.

53.

54.

55.

56.

57.

58.

59.

60.

61.

228

J. Butler and H. Windischmann, “Developments in CVD-Diamond Synthesis
During the Past Decade,” MRS Bulletin, vol. 23, no. 9, pp. 22-27, 1998.

PD. Ownby and R.W. Steward, “Engineering Properties of Diamond and
Graphite,” in Metals Handbook, vol. 4, pp. 821-834. Washington, DC: ASM,
1989,.

S. Shitata, “The Road to Commercialization of Vapor-Phase-Grown Diamond,”
MRS Bulletin, vol. 23, no. 9, pp. 61-65, 1998.

GS. Yang, “Technology of CVD Diamond Thermister and Thin Film Heater,”
Doctoral Dissertation, Dept. of Electrical and Computer Engineering, Michigan
State University, East Lansing, 1996.

A. Masood, “Technology and Electronic Properties of Diamond Film
Microsensors for Thermal Signals,” Doctoral Dissertation, Dept. of Electrical and
Computer Engineering, Michigan State University, East Lansing, 1991.

K. Hirabayashi, Y. Taniguchi, O. Takamatsu, T. Ikeda, K. Ikoma, and N. Iwasaki-
Kurihara, “Selective Deposition of Diamond Crystals by Chemical Vapor

Deposition Using a Tungsten-Filament Method,” Applied Physics Letters, vol. 53,
no. 19, pp. 1815-1817, 1988.

A. Masood, M. Aslam, M.A. Tamer, and TJ. Potter, “Techniques for Patterning
CVD Diamond Films on Non-diamond Substrates,” Journal of Electrochemical
Society, vol. 138, no. 11, pp. L67-L68, 1991.

J. McCluskey and F. Doherty, Engineering Materials Handbook, vol. 4. Metals
Park, OH: ASM, 1990.

B. Wright, “Processing Parameters for MPCVD Diamond Films,” Data Base,

Dept. of Electrical and Computer Engineering, Michigan State University, East
Lansing, 1999.

U. Brinkmann, “Long-Term Stability of the 248-nm Beam Proﬁle,” Lambda
Physik: Highlights, no. 23, pp. 6-7, 1990.

D. Halliday and R. Resnick, Fundamentals of Physics, 3 ed. New York, NY: John
Wiley & Sons, 1988.

62.

63.

65.

66.

67.

68.

69.

70.

71.

229

D.W. Jones, Control of Stepping Motors, a tutorial.
httpzllwww.cs.uiowa.edu/%7Ejoneslstep/: University of Iowa, Department of
Computer Science, 1998.

D. Devaux, R. Fabbro, L. Tollier, and E. Bartnicki, “Generation of Shock Waves
by Laser-Induced Plasma in Conﬁned Geometry,” Journal of Applied Physics,
vol. 74, no. 4, pp. 2268-2273, 1993.

P. Peyre, R. Fabbro, L. Berthe, and C. Dubouchet, “Laser Shock Processing of
Materials, Physical Processes Involved and Examples of Applications,” Journal
of Laser Applications, vol. 8, pp. 135-141, 1996.

R. Srinivasan and V. Mayne-Banton, “Self-Developing Photoetching of
Polymthylene Terephthalate) Films by Far-Ultraviolet Excimer Laser Radiation,”
Applied Physics Letter, vol. 41, no. 6, pp. 576-578, 1982.

K. Mukherjee, T.H. Kim, and W.T. Walter, “Shock Deformation and
Microstructural Effects Associated with Pulse Laser-Induced Damage in Metals,”
Lasers in Metallurgy, (K. Mukherjee and J. Mazumder, Eds.), pp. 137-150,
Chicago, IL: The Metallurgical Society of AIME, 1981.

CG. Wakade, N.B. Dahotre, and K. Mukherjee, “Damage in Aluminum, Zinic
and Tin from a Nanosecond Electric Pulse Discharge,” Materials Science and
Engineering, vol. 64, pp. 247-254, 1984.

Y. Iida and ES. Yeung, “Optical Monitoring of Laser-Induced Plasma Derived
from Graphite and Characterization of the Deposited Carbon Film,” Applied
Spectroscopy, vol. 48, no. 8, pp. 945-950, 1994.

X. Chen and J. Mazumder, “Emission Spectroscopy During Excimer Laser

Ablation of Graphite,” Applied Physics Letters, vol. 57, no. 2178-2180, p. 431,
1990.

J.E. Mental] and R.W. Nicholls, “Spectroscopic Temperature Measurements on
Laser-Produced Flames,” Journal of Chemical Physics, vol. 46, no. 8, pp. 2881-
2885, 1967.

B. Holzapfel, K. Kammer, and L. Schultz, “PLD Plume Diagnostics by High-
Speed ICCD Photography,” Lambda Physik: Science Report, no. 7, pp. 1-3, 1996.

72.

73.

74.

75.

76.

77.

78.

79.

80.

81.

82.

83.

230
DJ. Rawlins, Light Microscopy. Oxford, UK: BIOS Scientiﬁc, 1992.
CL. Mantel], Carbon and Graphite Handbook. Huntington, NY: Krieger, 1979.

J. Sneddon, T.L. Thiem, and Y. Lee, Lasers in Analytical Atomic Spectroscopy.
New York, NY: VCH Publishers, 1997.

M.W. Geis, M. Rothschild, R.R. Kunz, R.L. Aggarwa], K.F. Wall, C.D. Parker,
K.A. McIntosh, N.N. Efremow, J .J . Zayhowski, D.J. Ehrlich, and J.E. Butler,
“Electrical, crystallographic, and optical properties of ArF laser modiﬁed
diamond surfaces,” Applied Physics Letters, vol. 55, no. 22, pp. 2295-2297, 1989.

AR. Date and AL. Gary, Applications of Inductively Coupled Plasma Mass
Spectrometry. New York, NY: Chapman and Hall, 1989.

R.K. Winge, V.A. Fassel, V.J. Peterson, and M.A. Floyd, Inductively Coupled
Plasma-Atomic Emission Spectroscopy. New York, NY: Elsevier Science, 1985.

L.J. Radziemski and DA. Cremers, Laser-Induced Plasmas and Applications,
vol. Marcel Dekker. New York, NY, 1989.

B.W. Shore and DH. Menzel, Principles of Atomic Spectra. New York, NY: John
Wiley & Sons, 1968.

D.L. Andrews, Applied Laser Spectroscopy: Techniques, Instrumentation, and
Applications. New York, NY: VCH Publishers, 1992.

D. Papousek and MR. Aliev, Molecular Vibrational-Rotational Spcetra. New
York, NY: Elsevier Scientiﬁc, 1982.

J. Sneddon, T.L. Thiem, and Y.-I. Lee, “Analytical Atomic Spectroscopy,” in
Lasers in Analytical Atomic Spectroscopy, (J. Sneddon, T.L. Thiem, and Y.-I.
Lee, Eds.), pp. 13-14. New York, NY: VCH Publisher, 1997,.

L.J. Radziemski, “Review of Selected Analytical Applications of Laser Plasmas

and Laser Ablation, 1987-1994,” Microchemical Journal, vol. 50, no. 3, pp. 218-
234, 1994.

84.

85.

86.

87.

88.

89.

90.

91.

92.

93.

94.

95.

231

RA. Cairns, Plasma Physics. Philadelphia, PA: Heyden & Son, 1985.
HR. Griem, Plasma Spectroscopy. New York, NY: McGraw-Hill, 1964.

HR. Griem, Spectral Line Broadening by Plasmas. New York, NY: Academic
Press, 1974.

J .H. Eberly and P. Lambropoulous, Multiphoton Processes. New York, NY:
Wiley, 197 8.

X. Xu and K.H. Song, “Radiative Transfer in Pulsed-Laser-Induced Plasma,”
Journal of Heat Transfer, vol. 119, pp. 502-508, 1997.

EA. Rohlﬁng, “Optical Emission Studies of Atomic, Molecular, and Particulate
Carbon Produced from a Laser Vaporization Cluster Source,” Journal of
Chemical Physics, vol. 89, no. 10, pp. 6103-6112, 1988.

HQ Liu, X.L. Mao, J.H. Y00, and RE. Russo, “Nonlinear Changes in Plasma
and Crater Properties During Laser Ablation of Si,” Applied Physics Letters, vol.
75, no. 9, pp. 1216-1218, 1999.

V. Detalle, J.L. Lacour, P. Mauchien, and A. Semerok, “Investigation of Laser
Plasma of Solid Element Composition Microanalysis,” Applied Surface Science,
vol. 138, no. 139, pp. 299-301, 1999.

PH. Heckmann and E. Trabert, Introduction to the Spectroscopy of Atoms. New
York, NY: Elsevier Science, 1989.

W.G. Richards, Structure and Spectra of Molecules. New York, NY: John Wiley
& Sons, 1985.

AR. West, Molecular Spectroscopy. London: Heyden and Son, 1977.

WC. Martin, J. Sugar, A. Musgrove, W.L. Wiese, J .R. Fuhr, D.E. Kelleher, K.
Olsen, and R]. Mohr, “NIST Atomic Spectra Database, NIST Standard Reference

Database #78, version 2.0,” http://physics.nist.gov/cgi-bin/AtData/main_asd,
1999.

96.

97.

98.

99.

100.

101.

102.

103.

104.

105.

106.

232

R.W. Pearse and A.G. Gaydon, The Identiﬁcation of Molecular Spectra, 3rd ed.
New York, NY: John Wiley & Sons, 1963.

W. Weltner and R.J.V. Zee, “Carbon Molecules, Ions, and Clusters,” Chemical
Review, vol. 89, pp. 1713-1747, 1989.

SS. Harilal, R.C. Issac, C.V. Bindhu, V.P.N. Nampoori, and C.P.G. Vallabhan,
“Temporal and spatial evolution of C2 in laser induced plasma from graphite
target,” Journal of Applied Physics, vol. 80, no. 6, pp. 3561-3565, 1996.

EA. Rohlﬁng, D.M. Cox, and A. Kaldor, “Production and characterization of

supersonic carbon cluster beams,” Journal of Chemical Physics, vol. 81, no. 7, pp.
3322-3330, 1984.

M. Anselment, R.S. Smith, E. Daykin, and F. Dimauro, “Optical Emission Studies
on Graphite in a Laser/Vaporization Supersonic Jet Cluster Source,” Chemical
Physics Letters, vol. 134, no. 5, pp. 444-449, 1987.

J. Robertson and ER O'Reilly, “Electronic and Atomic Structure of Amorphous
Carbon,” Physical Review B, vol. 35, no. 6, pp. 2946-2957, 1987.

D. Beeman, J. Silverrnan, R. Lynds, and MR. Anderson, “Modeling Studies of
Amorphous Carbon,” Physical Review B, vol. 30, no. 2, pp. 870-875, 1984.

C. Champeaux, D. Damiani, J. Aubreton, and A. Catherinot, “Mass Spectrometric
Investigation of the KrF Laser-Induced Plasma Plume Created above an YBaCuO
Superconducting Target: Correlation with Thickness Distribution of Deposited
Thin Films,” Applied Surface Science, vol. 69, pp. 169-173, 1993.

M. Kuzuya, H. Matsumoto, H. Takechi, and O. Mikami, “Effect of Laser Energy
and Atmosphere on the Emission Characteristics of Laser-Induced Plasma,”
Applied Spectroscopy, vol. 47, no. 10, pp. 1659-1664, 1993.

L. Pauling and S. Goudsmit, The Structure of Line Spectra. New York, NY:
McGraw-Hill, 1930.

Y.-i. Lee and J. Sneddon, “Ambient Gas Breakdown Behavior in an Excimer
Laser-Ablated Plasma,” Microchemical Journal, vol. 50, pp. 235-243, 1994.

107.

108.

109.

110.

111.

112.

113.

114.

115.

116.

233

RJ. Nordstrom, “Study of Laser-Induced Plasma Emission Spectra of N2, 02 and
Ambient Air in the Region 350 nm to 950 nm,” Applied Spectroscopy, vol. 49, no.
10, pp. 1490-1499, 1995.

G. Herzberg, Molecular Spectra and Molecular Structure. Princeton, NJ: D. Van
Nostrand, 1950.

J .R. Ridge, “Investigation of a Carbon Rod Atomization System for Laser
Induced Breakdown Spectroscopy,” Dept. of Chemistry, Michigan State
University, East Lansing, MI, 1993.

DJ. Kalnicky, V.A. Fassel, and RN. Kniseley, “Excitation Temperature and
Electron Number Densities Experimented by Analyte Species in Inductively
Coupled Plasmas with and without the Presence of an Easily Ionized Element,”
Applied Spectroscopy, vol. 31, no. 2, pp. 137-150, 1977.

C. N aulin, M. Costes, and G. Dorthe, “C2 Radicals in a Supersonic Molecular
Beam,” Chemical Physics Letters, vol. 143, no. 5, pp. 496-500, 1988.

T.P. Duffey, T.G. McNeela, and J. Mazumder, “Absorption Spectroscopic
Measurement of Atomic Density in Laser-Induced Vapor Plume,” Laser
Materials Processing, (P. Denney, I. Miyamoto, and BL. Mordike, Eds.), pp.
127-133, Orlando, FL: ICALEO, 1993.

J .M. Green, W.T. Silfvast, and O.R.W. 11, “Evolution of a CO2-1aser-produced

cadmium plasma,” Journal of Applied Physics, vol. 48, no. 7, pp. 2753-2761,
1977.

G. Koren and J .T.C. Yeh, “Emission spectra and etching of polymers and graphite

irradiated by excimer lasers,” Journal of Applied Physics, vol. 56, no. 7, pp. 2120-
2126, 1984.

DE. Powers, S.G. Hansen, M.E. Geusic, D.L. Michalopoulos, and R.E. Smalley,

“Supersonic Copper Clusters,” Journal of Chemical Physics, vol. 78, no. 6, pp.
2866-2881, 1983.

B. Holzapfel, B. Roas, L. Schultz, P. Bauer, and G. Saemann-Ischenko, “Off-axis
laser deposition of YBazCu3O7 - 5 thin ﬁlms,” Applied Physics Letters, vol. 61,
no. 26, pp. 3178-3180, 1992.

117.

118.

119.

120.

121.

122.

234

W.D. Callister, Materials Science and Engineering an Introduction, 4th ed. New
York, NY: John Wiley & Sons, 1997.

J .K. Park, J .D. Howard, C.W. Chen, and K. Mukherjee, “Laser Processing of
Polymer Composites for Adhesive Bonding,” Proceeding of the American Society
for Composites 14th Technical Conference, (J .M. Whitney and J .E. Saliba, Eds.),
pp. 661-667, Dayton, OH: Technomic Publishing Inc., September 1999.

S. Gloor, S.M. Pimenov, E.D. Obraztsova, W. Luthy, and HP. Weber, “Laser
Ablation of Diamond Films in Various Atmospheres,” Diamond and Related
Materials, vol. 7, pp. 607-611, 1998.

J .K. Park, V.M. Ayres, J. Asmussen, and K. Mukherjee, “Maskless Patterning on
Ultra-Hard Film Materials,” presented in MRS 99 fall meeting, accepted for
publication in Materials Research Society, 1999.

J .K. Park, V. Ayres, J. Asmussen, and K. Mukherjee, “Precision Micromachining
on CVD Diamond Films,” accepted for publication in Diamond and Related
Materials, 1999.

J.-F. Lei, L.C. Martin, and HA. Will, Advances in Thin Film Sensor Technologies
for Engine Applications. Washington, DC: National Aeronautics and Space
Administration, 1997.