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6/01 c:/CIRC/DatoDue.p65—p. I 5

POLY-C TECHNOLOGIES FOR FIELD EMISSION
ELECTROLUMINESCENCE

BY

Ungsik Kim

A DISSERTATION
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY
Department of Electrical and Computer Engineering

2002

ABSTRACT
POLY-C TECHNOLOGIES FOR FIELD EMISSION ELECTROLUMINESCENCE
By

Ungsik Kim

Poly-crystalline diamond and carbon nanotube, with their unique
mechanical, thermal, chemical and electrical properties, are attractive
materials for field emission display applications. The research reported in
this thesis concerns the investigation of electron emission and electro-
luminescence during electron emission from diamond and carbon
nanotube.

Diamond and carbon nanotube emitters were fabricated under
various growth conditions using microwave plasma chemical vapor
deposition system. Methane concentration in hydrogen and extrinsic
doping of boron were used to vary the defect density in diamond films.

Various shapes of multi-wall carbon nanotubes with diameters ranging

from 20 - 400 nm and densities in the range of 108- 109 cm"2 were grown on

iron and nickel coated substrates.

The spatial mapping of electron emission over the sample surface
was achieved by computer controlled x-y-z stages with 1 pm resolution in a
vacuum chamber. The mapping study revealed that secondary nucleation
on the diamond film surface which resulted in an increase of density of

grain boundaries played an important role in improving the electron

emission. Vertically aligned carbon nanotubes improved dramatically the
site density and uniformity of electron emission. Carbon nanotubes were
grown on a pointed metal tip with a radius of a few microns. It was
demonstrated that the tube on a tip could be used as single electron
source.

We have reported for the first time field emission electro-
luminescence (FEEL) from poly-crystalline diamond although light
emission during field emission from carbon nanotube was observed by
other researchers. The analysis of spectral data indicated that the defects
present in the film served as luminescent centers. The quantitative models
for FEEL and hysteresis behavior of emission current were discussed.
FEEL is potentially attractive for display devices without the need for

phosphor-coated screens.

ACKNOWLEDGEMENTS

The author wishes to thank his advisor, Dr. Dean Aslam, for his
encouragement, guidance and support throughout this research.
Additional thanks are extended to Dr. Donnie K. Reinhard, Dr. Timothy A.
Grotjohn and Dr. David Tomanek for their valuable discussions and
academic advices. The author is also thankful to Dr. Steve Rand of
University of Michigan for help in developing the qualitative model.

The author would like to thank all the members of Dr. Aslam’s
research group for their assistance and helpful discussions.

Last but not least, the author would like to thank his family in Korea
and his wife, Dayoung Kim, for their patience, understanding and sacrifice
during the course of this study.

This work was supported in part by the Engineering Research
Centers Program of the National Science Foundation under Award Number

EEC-9986866.

TABLE OF CONTENTS

LIST OF TABLES .............................................................................. vii
LIST OF FIGURES .............................................................................. viii
1. RESEARCH MOTIVATION AND GOALS
1.1 Introduction .......................................................................... 1
1.2 Objective of This Work ............................................................ 2
1.3 Dissertation Organization ....................................................... 5

2. DIAMOND AND CARBON NANOTUBES: A REVIEW

2.1 Introduction ......................................................................... 7
2.2 A Review of Diamond ............................................................ 7
2.2.1 Properties of Diamond ................................................ 7
2.2.2 Field Emission from Diamond ..................................... 10
2.2.3 Luminescence from Diamond ..................................... 17
2.3 A Review of Carbon Nanotubes ............................................ 23
2.3.1 Properties of Carbon Nanotubes ............................... 23
2.3.2 Fabrication of Carbon Nanotubes .............................. 29
2.3.3 Field Emission from Carbon Nanotubes ...................... 35
2.3.4 Luminescence from Carbon Nanotubes ....................... 39

3. POLY-C TECHNOLOGY

3.1 Introduction ........................................................................ 43
3.2 Fabrication System .............................................................. 43
3.3 CVD Diamond Technology .................................................... 50
3.3.1 Nucleation .............................................................. 50
3.3.2 Patterning ............................................................... 55
3.3.2.1 Photolithographic Method ............................. 56

3.3.2.2 Direct Patterning Method .............................. 58

3.3.3 Doping ................................................................... 72
3.3.4 Characterization ...................................................... 76

3.4 Carbon Nanotube Technology ................................................ 78
3.4.1 Catalyst/Patterning ................................................... 78
3.4.2 Growth Study .......................................................... 79
3.4.2.1 Growth ........................................................ 79

3.4.2.2 Purification ................................................ 96

3.4.3 Characterization ...................................................... 96

3.5 Summary ........................................................................... 97

4. FIELD EMISSION CHARACTERIZATION

4.1 Introduction ........................................................................ 99
4.2 Field Emission Characterization System .................................. 99

4.3 Field Emission/Mapping Study ............................................. 104
4.3.1 CVD Diamond .......................................................... 104
4.3.1.1 Field Emission .......................................... 104
4.3.1.2 Field Emission Mapping ............................. 112
4.3.2 Carbon Nanotubes ................................................... 122
4.3.2.1 Carbon Nanotube Film ............................... 123
4.3.2.2 Nanotubes on a pointed tip ......................... 127
4.4 Summary ............................................................................ 140

5. FIELD EMISSION ELECTRO-LUMINESCENCE (FEEL) IN POLY-C
5.1 Introduction ...................................................................... 142
5.2 Field Emission Electro-luminescence Characterization Setup..142
5.3 Field Emission Electro-luminescence .................................. 144
5.3.1 CVD Diamond .......................................................... 144
5.3.2 Carbon Nanotubes ................................................... 153
5.4 Qualitative Model ............................................................... 155
5.4.1 Field Emission Electra-luminescence ....................... 155
5.4.2 Hysteresis Loop ..................................................... 157
5.5 Summary ......................................................................... 163

6. CONCLUSIONS AND FUTURE RESEARCH

6.1 Summary and Conclusions ................................................. 164
6.2 Future Research ............................................................... 165
BIBLIOGRAPHY ................................................................................ 166

vi

2-1 :
2-2:
2-3:

2-4:

3-2:

4-1:

4-3:

LIST OF TABLES

Properties of diamond ................................................................ 9
Diamond field emitters .............................................................. 12
Luminescence spectra in diamond .............................................. 18
Carbon nanotube field emitters ................................................... 36
Details of diamond powder loaded fluid ..................................... 51
Summary of carbon nanotube growth conditions ......................... 80

Grain densities and electric fields to achieve 1IIIA/cm2 for diamond
grown at 6000 ....................................................................... 108

Summary of deposition conditions and field emission current
density ................................................................................... 113

Etchant for electrolytic etching of nickel and iron wires ............. 129

vii

1-1:

2-5:

2-6:
2-7:
2-8:
2-9:

2-10:

3-1:

3—3:

3-4:

3-5:

LIST OF FIGURES

Overview of poly-C field emission electro-luminescence ................. 3
(a) Unit cell of diamond structure and (b) band structure of
diamond .................................................................................... 8

EL and CL spectra of boron-doped poly-diamond. (a) 8/0 = 200ppm.

(b) B/C = 1000ppm .................................................................... 21
(i) Schematic diagram of experimental setup and (ii)
electroluminescence spectra at different voltages ........................ 22
Construction of the unit cell for (2,3) nanotube ............................ 25

Raman Spectra of (a) highly oriented pyrolytic graphite, (b) inner
core of the cathodic deposit, (0) outer shell of the cathodic deposit,

and (d) glassy carbon ........................................................... 26
Schematic diagram of arc discharge .......................................... 30
Schematic diagram of laser ablation .......................................... 31
Schematic diagram of catalytic growth ......................................... 32
Model of the tip of a multiwalled nanotube ................................. 41

Luminescence spectra. (a) Variation of emitted current for MWNT and

(b) Different MWNTs with different emitted currents ....................... 42
An overview of poly-C technology ............................................. 44
Schematic diagram of MPCVD system ......................................... 46
The side view of the microwave cavity, the baseplate, and the
deposition chamber of the system ............................................... 47
Diamond nucleated by brush-coating of N10 .............................. 52

DW Spin coating; (a) spin/growth, (b) spin/growth/spin/growth, and
(c,d) spin/growth/spin/growth/spin/growth. The sample is spun at
2500 rpm for 20 sec, followed by 5 min growth ............................. 53

viii

3-6:
3-7:

3-8:

3-10:

3-11:
3-12:

3-13:

3-14:
3-15:
3-16:
3-17:
3-18:
3-19:
3-20:

3-21 :

3-22:

3-23:

3-24:

3-25:

DW coated Si structures ............................................................ 54

Schematic diagram of DPR patterning process ........................... 57
Schematic diagram of the direct patterning system ....................... 59
Substrate stage and nozzle ........................................................ 60

Block diagrams of (a) flow controller unit and (b) temperature

controller unit ........................................................................... 63
Detail specification of needle valve .............................................. 64
Detail specification of spray valve ............................................. 65

Diamond patterns on 4 inch substrate using direct patterning

system ..................................................................................... 67
Diamond patterns by needle valve ............................................... 68
Diamond coated by spray nozzle ................................................. 69
Line patterns by spray nozzle .................................................... 70
Diamond patterns generated by printer ........................................ 71
Resistivity versus TMB flow ..... A ................................................. 74
The growth temperature dependence of resistivity ....................... 75
Carbon nanotubes grown for 15 min at (a) 650 C and (b) 7500 ........ 82

Energy dispersive spectroscopy of clusters deposited on carbon
nanotubes .............................................................................. 83

(a) Schematic diagram of growth setup and (b,c,d,e) spiral growth of
carbon nanotubes ..................................................................... 84

Carbon nanotubes grown for (a) 30 sec and (b) 120 min ............... 85

Carbon nanotubes grown for 10 min with (a) 2% and (b) 8% CH4 in H2
and N2 ...................................................................................... 86

(a,b) Lateral growth and (c,d) vertical growth of Carbon nanotube..87

ix

L“

3-26:

3-27:
3-28:
3-29:
3-30:

3-31 :

4-1 :
4-2:

4-3:

4-4:

4-5:

4—6:

4-7:

Carbon nanotubes grown for 15 min at 650 C on (a) Fe and (b) Ni

coated substrates ..................................................................... 88
Macaroni shape of carbon nanotubes ........................................... 91
TEM micrographs Of carbon nanotubes ..................................... 92
Gear Patterned carbon nanotubes ............................................... 93
Square patterned carbon nanotubes ............................................ 94

(a) As-grown carbon nanotubes and (b) carbon nanotubes subjected

to ultrasonic treatment ............................................................... 95
Setup of field emission characterization system .......................... 100
Electrical setup for field emission measurement .......................... 102

SEM micrographs of DPR deposited at (a) 500 C, (b) 550 C, and (c)
600 C for two hours ................................................................ 106

Setup for field emission measurement using flat anode ............... 107

(a) I-V characteristics of diamond grown at 600 C with different
seeding methods and (b) Fowler-Nordheim plot of N10 film grown at
600 C ...................................................................................... 109

(a) l-V characteristics of DPR film grown at 500, 550, and 600 C and
(b) Fowler-Nordheim plot of DPR film grown at 600 C ................... 110

(a) SEM micrograph, (b) Raman spectra, and (c) field emission
mapping for diamond film deposited at 700 C with 1% CH4 in
H2 ........................................................................................ 114

(a) SEM micrograph, (b) Raman spectra, and (c) field emission
mapping for diamond film deposited at 700 C with 4% CH4 in
H2 .......................................................................................... 115

(a) SEM micrograph, (b) Raman spectra, and (0) field emission
mapping for diamond film deposited at 700 C with 7% CH4 in
H2 ........................................................................................ 116

4-13:

4-14:

4-15:

4-16:

4-17:

4-18:

4-19:

4-20:

4-21 :

4-22:

4-23:

4-24:

: (a) SEM micrograph, (b) Raman spectra, and (0) field emission

mapping for diamond film deposited at 600 C with 4% CH4 in
H2 ........................................................................................ 118

: (a) Raman spectra and (b) field emission mapping for free-standing

diamond film ........................................................................... 120

: (a) SEM micrograph, (b) Raman spectra, and (c) field emission

mapping for free-standing diamond film deposited at 700 C with 4%
CH4 in H ................................................................................. 121

(a) SEM micrograph and (b) field emission mapping for carbon
nanotube film grown at 650 C .................................................... 124

(a,b) SEM micrographs and (c) field emission mapping for carbon
nanotube film of Figure 4-13 after cleaning ................................ 125

(a) SEM micrograph, (b) l-V characteristics, and (c) field emission
mapping for highly oriented carbon nanotube film ..................... 126

Diagram of electrolytic etching setup ....................................... 129

SEM micrographs of nickel wires after electrolytic etching. (a) 100
pm, (b) 200 pm, (0) 500 pm, and (d) 1000 um ............................... 130

Diagrams of wire placement in MPCVD. (a) side view and (b) top view
of configuration 1, (b) side view and (0) top view of configuration

2 ........................................................................................... 132
(a—d) SEM micrographs of nanotubes grown on Fe tips ............... 133
(a,b) SEM micrographs of nanotubes grown on Ni tips ................ 134

Measurement setup of field emission from carbon nanotubes on a
pointed tip .............................................................................. 135

(a) SEM micrograph and (D) W characteristics of nanotubes grown
on Fe tip. The inset is Fowler-Nordheim plot ............................. 136

(a) SEM micrograph and (b) l-V characteristics of nanotubes grown
on Ni tip. The inset is Fowler-Nordheim plot ................................ 137

SEM images of nanotubes on Fe tip: (a,b) as grown and (c,d) after
field emission measurement at 6.7 ILA ....................................... 138

xi

5-3:

5-4:

5-5:

5-6:

5-7:
5-8:
5-9:

5-10:

5-11:

Schematic diagram of field emission electro-luminescence
characterization setup ............................................................ 143

I-V characteristics with and without FEEL for undoped
polycrystalline diamond film ..................................................... 145

IN characteristics with FEEL from B-doped free-standing diamond

film ...................................................................................... 146
l-V characteristics with FEEL from undoped poly-diamond ........... 147
Luminescence spectra from B-doped free-standing diamond
film ........................................................................................ 150
Field emission mapping for B-doped poly-diamond ................... 151

(a) Luminescence spectra with variation of emission current and (b)
luminescence intensity as a function of emission current ............ 154

(a) Luminescence spectra of different FEEL Sites from carbon
nanotube film and (b) Spectra from MWNTs in literature [2.148]...151

Quantitative model of field emission electro-Iuminescence from poly-

diamond film ......................................................................... 156
Dependence of current on temperature. The straight lines are plots of
é-T— for different values of E ..................................................... 159

Replot of Figure 5-10; Dependence of current on electric field....160

xii

CHAPTER 1

RESEARCH MOTIVATION AND GOALS

1.1 Introduction

Devices based on microfabricated field emission sources were
proposed in the early 19603 [1]. The concept of molybdenum microtip
emitters was first developed by Spindt [2]. A variety of materials and
structures have been attempted thereafter to improve the performance Of
the devices [3,4,5]. The development of a new generation of flat panel
displays can be regarded as a strong driving force for stimulating the
research effort in the field of carbon cold cathodes. Various forms of
carbon based materials, such as CVD diamond film, amorphous carbon,
graphite, and carbon nanotubes, are being studied concerning both
fundamental and applied purposes in flat panel displays, microwave tubes
and point electron guns [6,7,8,9,10,11]. The ideal emitter has a high carrier
concentration and high mobility that results in good electrical conductivity
to keep up stable emission and to enable high speed applications. A high
electric field breakdown strength is also important to avoid destruction by
arching. The thermal conductivity should be sufficient that the heat
generated by the high current densities can be quickly dissipated. The

emitter medium should be chemically inert to avoid an emission decay

during ion bombardment or surface diffusion on the cathode surface. The
resistance to chemical attacks would make it possible to use a lower
vacuum without running into emission deterioration. High tensile strength
and low vapor pressure minimize mechanical surface damage due to high
electric field forces, and emission noise.

Diamond and carbon nanotubes have proven themselves as
excellent candidates for the next generation of electron-emission devices
[12,13]. Parallel investigations of both the physics of emission and
attempts for devices have taken places [6,14]. The original interest in
investigating emission properties of diamond stems from the fact that
certain orientations of diamond exhibit negative electron affinity [15,16].
This means that the vacuum level lies below the conduction band edge so
that electrons present in the conduction band can readily escape the
surface. The potential use of carbon nanotubes as a material for electron
emitter originates from the small diameter and elongated shape of the tube
that lead to a high geometrical field enhancement [17]. Another strong
point of carbon nanotube emitters is the relatively simple production in

large quantities [18.19].

1.2 Objective of This Work
The scope of the present work is to understand the electron
emissions of poly-diamond and carbon nanotubes and to gain a detailed

understanding of electro-luminescence during field emission.

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Figure 1.1 illustrates an overview of the present study. Infrastructure
technologies for diamond and carbon nanotubes are required to
successfully fabricate the emitter structures and related systems. The
deposition parameters, such as temperature, doping, gas mixture ratio and
pre/post-growth treatment, influence the film morphology and defect
contents. Although nanotube geometric structures appear to be ideally
suited as field emission, the orientation and density of the tubes are critical
for emission properties. The electron emission characteristics with respect
to the density of nanotubes were reported [20]. The low density nanotube
film showed inhomogeneous emission with very few sites emitting a low
current. A much more homogeneous emission image was Obtained for a
medium density film. A very dense film yielded a result similar to the low
density film. The length of the tubes and the distance between neighboring
emitters are important to reach a high field enhancement along with an
emitter density that is high enough to ensure homogeneous emission at
low fields. To best utilize the characteristics of nanotubes for field
emission, the tubes should have highly oriented and well-distributed. The
electron emission from the surface of diamond and nanotubes is non-
uniform which arises from non-uniformity of emission sites. It is, however,
not clear whether this non-uniformity is related to variation of electron
affinity, surface roughness, defects or grain size for diamond films and
orientation, defects or non-uniform distribution of nanotubes. l-V

characteristics and spectral data are expected to be helpful for

understanding the field emission electro-luminescence mechanism. A
model that can be used to explain the observed field emission induced

electro-luminescence will be made.

The present research mainly focuses on the following issues:

(1) The development of fabrication techniques for diamond and

carbon nanotube field emitters.

(2) Characterization of field emission/mapping and electro-

luminescence properties from fabricated emitters.

(3) Qualitative explanation of field emission electro-Iuminescence.

1.3 Dissertation Organization

Chapter 2 presents a brief overview of the current technologies of
diamond and carbon nanotubes. Unique properties of diamond and
nanotubes are reviewed. It considers the various methods for synthesizing
nanotubes, including arc evaporation and catalytic growth. Field emission
studies from various types of diamond and nanotubes are summarized.
Defects in diamond investigated by luminescence techniques are
discussed. Luminescence researches on diamond and carbon nanotubes

are also given. In chapter 3, poly-C technologies used in this study are

outlined. The detail description of the film deposition system, MPCVD, is
given. Nucleation, patterning, doping, and characterization of diamond film
are investigated. Nanotube growth procedure and method of purifying
tubes are also covered. Chapter 4 focuses on the characterization of field
emission from diamond and carbon nanotube films as well as nanotubes
on a pointed metal tip. The computer controlled system iS used to study a
spatial mapping Of electron emission over the sample surface. In chapter 5,
experimental observations of electroluminescence during field emission
are described. The qualitative models for field emission
electroluminescence and hysteresis behavior Of emission current are
proposed. Chapter 6 presents conclusions of this study and considers

possible future directions.

CHAPTER 2

DIAMOND AND CARBON NANOTUBES:

A REVIEW

2.1 Introduction

An overview of diamond and carbon nanotube films is presented.
The properties of the films are discussed. The fabrication of carbon
nanotubes (CNT) using different methods is described. Various types of
poly-diamond (poly-C) and CNT field emitters are summarized.

Luminescence studies are reported in detail.

2.2 A Review of Diamond

The unique electrical, chemical, thermal and mechanical properties
of poly-diamond as a field emitter are reported. Comprehensive field

emission and luminescence studies from diamond are discussed.

2.2.1 Properties of Diamond

Diamond is comprised of covalently bonded carbon atoms in a

diamond cubic crystal structure, shown in Figure 2-1(a).

       

(b)

 

 

 

Energv (eV)

 

 

 

 

 

 

 

T Conduction
band minimum

Valence band

maximum

Figure 2-1: (a) Unit cell of dlamond structure and
(b) band structure of diamond.

Table 2-1:

Properties of diamond.

 

Lattice constant

0.356725 nm

 

Atom density

1.77 x 1027 cm'3

 

2

 

 

 

 

 

 

 

 

 

 

 

 

Hardness 5700-10,400 kg/mm
Young’s modulus 10,5 x 1011 N/m2
Density 3.515 g/cm3
3:53:22? of thermal 0.8 x 10-6 C
Thermal conductivity 20 W/cm'K
Specific heat 6.195 J/K'mol
Melting point 4000 C
Refractive index 2.42

Band gap 5.45 eV
Resistivity (Ila) >1014 Q'cm
Dielectric constant 5.7

Hole mobility 1600 cm2N's
Electron mobility 2000 cmzN's

 

Electron saturated current
velocity

2.7 x 107 cm/s

 

Hole saturated current velocity

1 x107 cm/s

 

Electric breakdown field

1 x107 V/cm

 

Johnson figure of merit

73856 x 1023 w-O/s.2

 

 

Keyes figure Of merit

 

444 x 102 W'C/cm's

 

 

The diamond lattice can be thought of as a face centered cubic (FCC)
structure with an extra atom placed at a/4 + b/4 + 0/4 from each Of the FCC
atoms with a, b, c being the basis vectors of the lattice. Therefore, four

additional points within every unit cell are occupied by atoms resulting

from two interpenetrating FCC sublattices. In diamond covalent spa-

bonding is found, which distinguishes it from other carbonaceous

structures with different hybridization. Diamond with its low dielectric

constant 5, = 5.7 has a high electrical breakdown field strength of 107 V/cm

for undoped diamond, and a high electron saturation velocity at 2.7x107

cm/s which is favorable for high speed applications [21]. It is not very
reactive so that surface contaminations are of lesser concern. A thermal
conductivity of 20 W/cm'K enables a quick dissipation of heat induced by
high emission current [22]. In addition, diamond has a low coefficient of
thermal expansion at room temperature. In the [111] direction, electron
affinity is very small or even negative [15] whereas defect density and
stress are high. Diamond has an indirect band gap of 5.45 eV, as depicted
in Figure 2-1(b). Due to its large band gap, diamond is an insulator, in the

absence of dopants, at room temperature with a resistivity on the order of

>1014 Sicm [23]. The properties of diamond are summarized in Table 1.

2.2.2 Field Emission from Diamond

10

The wide bandgap of diamond produces interesting effect. The
conduction band approaches the vacuum level. The energy difference
between the vacuum level and conduction band is known as the electron
affinity, while the work function is the energy difference between the Fermi
level and the vacuum level. The work function of most metals is 4 eV to 5
eV. In diamond, there is some evidence that the conduction band may
exceed the vacuum level, yielding a negative electron affinity [15,24].
Therefore, there is no potential barrier for the electron emission from the
conduction band. The electron emission current density is a function of not
only the barrier height, but also of the electron supply which in turn
depends on the electron concentration in the conduction band. Because of
the wide bandgap of diamond, to Obtain significant electron emission one
needs to populate the conduction band by doping or by injection of
carriers from a metal contact. While p-type doing of diamond has been
demonstrated, effective n-type doping is still unsuccessful. Nitrogen is an
n-type dopant in diamond but its energy level is significantly below the
bottom of the conduction band. Consequently, the increase of
concentration of electrons due to the nitrogen doping is insignificant.
Exact mechanisms of the electron injection from the metal contacts, as well
as of the electron transport through the diamond film remain subjects of
theoretical modeling and discussions [1225.26.27]. Diamond may promise

as a cold cathode electron source for use in flat panel displays [6,28].

11

 

 

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15

Theoretical considerations of electron emitters suggest that the desired
material would be one with a low work function. In addition to low
temperature emission, there are numerous benefits to an emission source
with a low work function. Emission sources often have a small radius Of
curvature to enhance the electric field. The emission is sensitive to
changes in the radius of curvature, but a low work function device would
be less sensitive to geometrical effects. The turn-on voltage to initiate
electron emission is reduced in a low work function material and is more
abrupt. Therefore, voltage variations do not alter the emission current as
significantly as in higher work function emitters with a more gradual turn-
on. Another benefit of a low work function material is that the saturation
emission current is higher in low work function devices. Based on these
benefits, the low work function of diamond may make it ideally suited for
field emission applications.

Several structures have been investigated for electron emission from
diamond. A diamond junction device [29], homoepitaxial diamond [30],
amorphous diamond [31], nano-crystalline diamond [32.33.34.35], and
polycrystalline diamond [36.87.38] have been demonstrated. Field emission
was studied from diamond films implanted [39,40,41] or doped by boron
[42,43,44,45], nitrogen [46,47,48,49], or phosphorous [50,51]. Diamond was
used as a tip for electron emission and these tips were made into an array
[7,52]. Diamond was also used as a coating on Si [53,54,55,56] and metal

tips [57,58]. Patterned diamond was investigated for electron emission

16

[59,60]. The resilience of diamond emission when exposed to oxygen at 10'

2 Torr was demonstrated [61]. In addition to a negative or low work function,

field enhanced electron emission may be generated by the formation of a
diamond tip with a small radius of curvature [62]. Field emission from

various types of diamond is summarized in Table 2-2.

2.2.3 Luminescence from Diamond

The luminescence spectra observed when excited states relax is
beneficial in assessing the properties of diamond. Cathodo-luminescence,
where states are excited with an electron beam, is probably the most
commonly used luminescence technique. Photo-luminescence is
generated when the sample is exposed to photons and electro-
luminescence is investigated when the excitation caused by an applied
voltage is sufficient to generate light. The peak position and description for

several common defects in diamond are summarized in Table 2-3.

. Cathode-luminescence (CL)

The wavelength of the emitted photon is related to the energy
difference of the transition that generated the light. Therefore. CL provides
information about the defect levels within a material. The CL spectrum
typically consists of sharp peaks and broad bands. The sharp peaks are
indicative of discrete transitions between energy levels whereas broad

bands indicate variable transition energies [72,73,74].

l7

Table 2-3:

Luminescence spectra In diamond.

 

 

Peak Peak
position position Name Description Reference
(eV) (nm)

5.15 240.7 Boron related acceptors [85]

4.97 249.4

4.65 266.6

4.582 270 Carbon interstitial [79]

3.188 388.8 Carbon interstitial and [78]
single nitrogen atom

2.85 435 Blue Broad band — dislocations [76]

band A

2.8 442 Growth induced [86]
dislocation

2.33 532 Doublet line - nitrogen [76]
related

2.355 526.3 Nitrogen-carbon [87]
interstitial complex

2.284 543

2.2 563 Green Broad band - thought to [76]

band A be related to boron

2.156 574.9 Single N and V [77]

1 .945 638 Vacancy [88]

1.9 652.4 Related to phosphorous [89]

1 .682 737 Silicon [80]

1.673 741 GRI Neutral vacancy [80]

 

18

CL is a near-surface technique. Typical acceleration voltages are 10 to 50
keV and correspond to emission depths of 0.5 to 17.7 pm. The CL spectrum
typically consists of broad bands and sharp zero phonon lines and their
sidebands. Two broad peaks are often observed and are referred to as
green and blue band A because they occur in the green and blue
wavelengths, respectively. The broad band was thought to be associated
with dislocations [75]. A comparison of the CL spectra and x-ray
topographic images revealed a strong correlation of the 2.85 eV band to the
dislocation density. The 2.2 eV band was thought to be attributed to a
boron related center [76]. The sharp peaks were often associated with
impurity atoms or aggregates. Nitrogen containing defects generated
numerous CL peaks. The most common nitrogen peaks occurred at 2.156,
2.33, 2.807. and 3.188 eV. The 2.156 eV defect was thought to consist of
nitrogen and a vacancy [77]. Near 2.33 eV, a doublet line occurred which
was thought to be related to nitrogen [76]. Separate lines at 2.807 and 3.188
eV were thought to be caused by a single nitrogen atom and a carbon
interstitial [78]. Another defect that was believed to be related to a carbon
interstitial occurred at 4.582 eV [79]. The 1.681 eV defect near neutral
vacancy defect was attributed to silicon [80]. The emission intensity of one
defect may vary with the concentration of other defects and the efficiency
of individual defects differs. Therefore, CL does not provide a quantitative

determination of the defect density.

19

. Photo-luminescence (PL)

Laser light is Often used for PL [81.82.83]. The luminescence occurs
from defects with lower energy than the incident photons. This feature
allows selective excitation of a defect by controlling the incident laser
energy. The intense beam can excite lower concentration of defects. The

PL spectra are similar to the CL spectra for most defects.

. Electra-luminescence (EL)

Although not as heavily investigated, EL generated by an applied
voltage is also used to characterize diamond. Yellow-green luminescence
was observed for Schottky barrier point contact probed at 300 C to 750 C
[84]. EL from Schottky diode of boron-doped poly-diamond was observed
[75]. Figure 2-2 shows EL spectra of the lightly doped and heavily doped
diamond films. respectively. EL was observable when the forward bias
across the diode exceeded 25 V or the reverse bias exceeded 20 V. The EL
spectra were similar in forward and reverse biases. The luminescent center
of EL was equal to that of CL.

Blue-green EL from free-standing diamond has been observed [90].

The ln203 transparent conductor and conducting epoxy were used for the

front and back contacts on the 15 pm thick free-standing diamond. EL was
observed with the unaided eyes from the individual 5-10 pm grains of the

diamond film. The peak position of EL occurred at 485 nm.

20

Photon Energy (eVl Photon Energy (WI
1.8 2'0 2.2 25 3:0 15 _ 1.8 2.0 2.2 2.5 3.0 3.5

(a) (b)

 

 

, Intensity 1cm.)
Intensity (o.u.)

 

 

 

 

 

 

100 560‘ 560 450 300 700 soo 500 1.00 ‘300
Wavelength. (nm) _ WOVOIM (nth)

Figure 2-2: EL and CL spectra of boron-doped poly-dlamond.
(a) BIC = 200ppm. (b) BIC = 1000ppm.

21

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  
  
 
 
    
   

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E 100 - -
53 l
50
l

 

 

.5 2.0 2.5— 3.0 35 4.0 I 4.5
Photon Energy (eV)

Figure 23: (i) Schematic diagram of experimental
setup and (ii) electroluminescence
spectra at different voltages.

22

It was proposed that the recombination of donor-acceptor pairs was
responsible for the emission of the Observed light. The donor was believed
to be nitrogen and the acceptor was probably boron. Nitrogen
contamination was likely from the wall of the reactor or from the relatively
poor vacuum during deposition. The trace of boron was likely to have been
carried over from deposition to deposition.

Blue-violet EL from 400 pm thick free-standing diamond has been
reported [91]. The electrical contacts were provided by Ti/Pt/Au. The EL
was Observed at voltages above 800 V which was a field Of 2 V/pm. Figure
2-3 shows schematics of experimental setup and EL spectra at different
voltages. The main luminescence band was centered at 3.0 eV. Additional
peaks at about 3.65 and 3.85 eV appeared at voltages above 1850 V. The
subgap photocurrent spectrum in the photon energy range from 1.7 to 5.0
eV revealed that there was a 3.0 eV transition of electrons or holes between

the conduction or valence band and the gap states.

2.3 A Review of Carbon Nanotubes

In this chapter, properties and fabrication methods of carbon
nanotubes are discussed. Electron emission research works from a variety
of nanotubes are summarized. A discussion is given of luminescence from

nanotubes.

2.3.1 Property of Carbon Nanotubes

23

A carbon nanotube is a graphene sheet. a simple planar assembly of
carbon atoms disposed in a honeycomb lattice. rolled into a cylinder. The
primary classification of a carbon nanotube consists of either one
cylindrical graphene sheet (single-wall nanotube, SWNT) or Of several
nested cylinders with an interlayer spacing of 0.34 — 0.36 nm (multi-wall
carbon nanotube, MWNT). The nanotube diameter varies from ~1 nm (for
SWNTs) to 400 nm (for MWNTs) and its lengths are usually well over 1 pm.
One of the most significant quantum properties of carbon nanotube is its
electronic structure which depends only on its geometry. The helical
geometry of the honeycomb lattice is called chirality of SWNT which is
unique to solid state physics [92]. The electronic structure of SWNT is
either metallic or semiconducting, depending on tube diameter and chiral
angle and does not require any doping. The diameter and chirality is

determined by a chiral vector.
0,, = na + mb = (n,m) (2.1)

where a and b are the unit vectors of graphene sheet as shown in Figure 2-
4. The chiral vector specifies the equator of SWNT. Any other geometry and
properties are defined by the two indices (n,m). Only armchair (n,n) and
zigzag (n,0) nanotubes have a mirror symmetry and that the other (n,m)
nanotube has a chiral symmetry. Metallic conduction occurs when

n — m = 30 (2.2)

where n and m are the integers which specify the tube’s structure and q is

an integer [93.94.95].

24

 

Figure 24: Construction of the unit cell for (2,3) nanotube.

25

 

(6‘)”; 1580
(b) 1574
(c)
1350
,- ‘v-f _ — “ “ .~
W

L l J J

 

 

 

 

1800 1400 1000 600
Wavenumber Shift (1/cm)

Figure 2-5: Raman Spectra of (a) highly oriented pyrolytic
graphite, (b) inner core of the cathodic deposit,
(0) outer shell of the cathodic deposit. and (d)

glassy carbon.

26

All armchair tubes and one out of three zigzag and chiral tubes are metallic.
The band structure of the nanotube shows a gap leading to
semiconducting behavior. with a bandgap that scales approximately with

the inverse of the tube radius.

Resistivity measurements on MWNT showed wide variations (5x10.6

— 0.8 Q‘cm). Since samples of MWNT are known to be structurally
heterogeneous, these results provide clear evidence that the electronic
properties of carbon nanotubes can vary greatly according to their
structure [18.96.97.98]. Raw cathodic soot had a resistivity of
approximately 0.01 Qcm [18]. The catalytically grown straight tubes of 8.5
nm and 13.9 nm in diameter had resistivity of 0.00195 and 0.00078 9cm,
respectively [97]. Nanotubes were annealed at 2850 C before carrying out
electrical measurements. Four metal leads were deposited with 1 pm of
distance between contacts to enable four-probe measurements. The
resistivity values were in the range of 0.0000051 and 0.8 9cm. A slight
increase in resistivity was observed with decreasing temperature [98]. The
resistivities of bundles of SWNTS were measured in the range of 0.000034
and 0.0001 £20m using MWNTS as voltage probes [99]. The resistivity of the
bundles increased with the temperature above 200 K.

Figure 2-5 shows the Raman spectra of material from nanotubes and
nanoparticles taken from the core of the cathode, with those from the outer

Shell of the cathodic deposit produced by arc evaporation process, and

27

with the spectra of highly oriented pyrolytic graphite and of glassy carbon

[100,101]. The strong peak which occurs in the region of 1580 cm'1 can be

assigned to Raman vibrations of graphite. while the band at around 1350

cm.1 can be attributed to disorder. However, the spectra do not give

detailed information about nanotube structure since the core deposit
contains nanotubes with a variety of different sizes and structures. There is
little difference between Raman spectra from purified and unpurified
nanotube samples [102].

The theoretical work predicted the Young’s modulus for nanotubes
close to that for a graphene sheet (1060 GPa) [103,104,105]. The
quantitative measurements of the mechanical properties of nanotubes were
carried out in the transmission electron microscopy (TEM) and atomic
force microscopy (AFM). The Young’s modulus ranged from 400 GPa to
4100 GPa [106.107.108.109]. Clusters of nanotubes were deposited on TEM
grids such that isolated tubes were extended for a considerable distance
into empty space. The Young’s modulus was estimated from 410 to 4150
GPa, with an average of 1800 GPa. The large spread in values resulted from
uncertainties in estimating the lengths Of the anchored tubes, and from the
presence of defects in the tube structures [106]. Scanning probe
microscopy enabled individual tubes to be manipulated directly. One end
of the tube was fixed, and then the bending force of the tube was
determined as a function of displacement. A linear curve for lateral force

versus displacement was observed from MWNTS. The results implied a

28

value of ~1.28 TPa for the Young’s modulus [110]. Carbon nanotubes were
subjected to large bending stresses using atomic force microscopy. The
tubes were not fixed at one end, but were supported on mica. It was found
that the tubes can be bent repeatedly through large angles without

fracturing [111].

2.3.2 Fabrication of Carbon Nanotubes

A description of arc evaporation method of nanotube synthesis is
given. This is a classic method of preparing MWNTS, and produces good
quality tubes. Carbon vapor condensation, pyrolysis, and electrochemical
methods are summarized. Catalytic method for producing MWNTS is

discussed.

. Arc evaporation

The arc discharge technique [112] has been in use for the production
of carbon fibers as depicted in Figure 2-6. The graphite electrodes are held
a short distance apart during arching. Some of the carbon which
evaporated from the anode re-condensed as a hard cylindrical deposit on
the cathodic rod. The deposit on the cathode contains both nanotubes and
nano—particles. A number of factors have been shown to be important in
producing a good yield of high quality nanotubes. The most important is

the pressure of the helium in the evaporation chamber [18].

29

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Helium Atmosphere
Graphite Anode
Plasma
/ I .............. Graphite Cathode
\\\
F Pump
DC Voltage Supply

 

 

Figure 2-6: Schematic diagram of arc discharge.

30

 

 

l l l l l l C/Ollector

Laser fl > 5575 I \

Pulse

 

 

 

    
 

 

 

 

 

 

 

 

 

 

 

 

 

Gas inlet
/ ‘ Gas
. T T I T T T QuartzTube
N2 Oven 11000

Figure 2-7: Schematic diagram of laser ablation.

31

 

Hill] I ] fem...

// Sample
Gas inlet
Gas
Outlet

 

 

 

 

 

 

 

:llllllll

Oven 720C

 

 

 

09H2 N,

Figure 2-8: Schematic diagram of catalytic growth-

32

Another important factor is the current flowing through the two electrodes.
The current is usually in the range of 50 - 100 A. TOO high a current will
result in a hard, sintered material with few free nanotubes. The current
should be kept as low as possible, consistent with maintaining a stable
plasma [113,114]. Efficient cooling of electrodes and the chamber has been
shown to be essential in producing good quality nanotube samples and
avoiding excessive sintering [115]. lijima et al. and Bethune et al. reported
that an arc discharge with a cathode containing metal catalysts (such as
cobalt. iron or nickel) mixed to graphite powder resulted in a deposit
containing SWNTs [17,116]. The yield of the method has been significantly
increased by optimizing the catalyst mixture and the deposition conditions

[19,117].

0 Carbon vapor condensation
Another method to grow nanotubes using condensation of carbon

vapor was demonstrated. An electron beam was used to evaporate graphite

in a high vacuum (10'6 Torr), and collected the material which condensed

on quartz [118]. Carbon vapor was produced by resistively heating a

carbon foil, and the vapor was condensed onto highly oriented pyrolytic

graphite, under a vacuum of 10'8 Torr [119]. The synthesis can be carried

out in a horizontal flow tube under a flow of inert gas. The flow tube was
heated to ~1200 C by a tube furnace as displayed in Figure 27. Laser

pulses entered the tube and struck a target consisting of a mixture of

33

graphite and a metal catalyst such as CO or Ni. SWNTS condensed from the
laser vaporization and were deposited on a collector outside the furnace

zone[120]

. Pyrolysis

MWNTS can be produced by the pyrolysis of benzene in the presence
of hydrogen. Benzene vapor and hydrogen were introduced into a ceramic
reaction tube in which a graphite rod was positioned to act as a substrate.
Microscope examination showed the presence Of MWNTS similar in
structure and quality to those produced by arc-evaporation, although the

yield appeared to be low [121].

o Electrochemical synthesis

An electrochemical synthesis of MWNTS involved the electrolysis of
molten lithium chloride using a graphite cell in which the anode was a
graphite crucible and the cathode was a graphite rod. The cathode was
immersed in the melt. A current was passed through the cell and then
water was added to dissolve the lithium chloride and reacted with the
lithium metal. Toluene was added to the aqueous suspension. The solid
material resulted through the treatment contain large numbers of rather
imperfect MWNTS. Both tubes and nanoparticles contained encapsulated

lithium chloride or oxide [122].

34

. Catalytic growth

The catalytic growth of nanotubes is based on the decomposition of
a hydrocarbon gas over a transition metal to grow nanotubes in a chemical
vapor deposition (CVD) reactor. as in Figure 2-8. In general, the catalytic
growth yields nanotubes of larger diameter as compared to the arc
discharge. along with a crystalline structure that is not perfectly
graphitized. The ends of the tubes are mostly open. For the production of
MWNTS acetylene is usually used as source of carbon atoms at
temperatures typically between 600 and 800 C. To grow SWNTs the
temperature has to be significantly higher (900 — 1200 C) due to the fact
that they have a higher energy of formation. Yield and average diameter of
tubes were varied by controlling the process parameters [123]. The type of
catalyst was found to control the formation of individual bundled tubes
[124]. The catalytic method is ideally suited to grow films of nanotubes on

planar substrates.

2.3.3 Field Emission from Carbon Nanotubes

Carbon nanotubes have attracted considerable attention as electron
sources. Their high conductivity, sharp tip and long, narrow shape make
useful field emitters, and some promising results have been achieved. The
intrinsic structural and chemical properties of the individual tube play a
role. The field emission behaviors for SWNTs [125,126,127] and MWNTS

[13,128,129] were studied.

35

 

 

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38

Differences in field emission were found depending on the geometry [8],
fabrication methods [9,130], and surface treatment [131] as well as between
closed and open tubes [8]. The density and orientation of the tubes on the film
influenced also the emission [8,129]. Field emission was investigated on
patterned films with different densities [132]. The low density film showed a
rather inhomogeneous emission pattern with very few sites emitting. A much
more homogeneous emission with a large number of emission sites was
obtained for a medium density. A film of high density yields a result similar to the
low density film. In addition to the work on arrays of nanotubes, field emission
was carried out on an individual tube [8,133]. This enabled to determine the field
emission characteristics of an individual tube. It was found that field emission
was dramatically enhanced when the tube was opened by laser vaporization or
oxidation [134]. A flat panel display was demonstrated employing a nanotube-
epoxy composite as the source [135]. A summary of field emission from different

types of nanotubes is given in Table 2-4.

2.3.4 Luminescence from Carbon Nanotubes

Rinzler et al. detected a very faint luminescence at the tip of individual
opened nanotube [134]. Individual nanotube was attached to graphite fiber

electrodes. The tip of tube was opened either by laser heating in high vacuum to

near sublimation temperature (~3000 C) or by exposure to several militorr of 02

while laser-heating the tip to 1000 to 1500 C. The field emission ranged from 0.5

to 1.5 uA at -100 to —110 V bias with 1 mm separation. The nanotube

39

incandesced dimly at the tip. The structures responsible for the incandescence
were individual linear carbon chains that had pulled out from the open edges of
the graphene sheets of the nanotube as shown in Figure 2-9. The dim
incandescence was due to the carbon chains heated by the emission current.
The tube was biased substantially above —1 10 V and field emitting more than 2
M suffered catastrophic bum-back events. This produced a single bright streak.
The incandescent flash that illuminated the side of the nanotube was caused by
resistive heating of the outermost layer unraveling down the side of the tube.
Bonard et al. observed light emission during electron field emission on SWNT
and MWNT films [155]. The light was emitted from the vicinity of the apex of the
tip. The light intensity was increased with emitted current. Luminescence was not
homogenous on the emitting surface as the intensity variations were detected.
Figure 2-10 showed the spectra acquired at different emitted currents. The peak
intensity and widths were varying between 1.73 and 1.83 eV and between 0.3
and 1 eV, respectively. For SWNT films, light was emitted at higher energies as
compared with MWNTS, but their behavior was comparable to those of MWNTs.
Theoretical calculations showed that the local density of states at the tip
presented sharp localized states with well-defined energy bands. It was thus
suggested that the luminescence was due to electronic transitions between

energy levels at the tip that are participating in the field emission.

4O

 

Figure 2-9: Model of the tip of a multiwalled nanotube.

41

 

 

m [‘43-]

 

 

 

 

 

 

MIMI-l

 

 

 

 

151.051.71.75 1.81.85 1.91.95 2
MW)

Figure 2-10: Luminescence spectra. (a) Variation of emitted current
for MWNT. (b) Different MWNTs with different emitted
currents.

42

CHAPTER 3

POLY-C TECHNOLOGY

3.1 Introduction

The fundamental technologies such as nucleation, patterning,
deposition, doping, post-growth treatment, and characterization used in the

study are discussed, as shown in Figure 3-1.

3.2 Fabrication System

Both poly-diamond and carbon nanotube films were synthesized
using microwave plasma chemical vapor deposition (Model MPDR 313EHP,
Wavemat, Inc.) with 2.45 GHz microwave generator up to 6 kilowatts. The
schematic diagram is shown in Figure 3-2. The main parts of the system
consist of;

(1) Cylindrical microwave cavity

(2) Process chamber

(3) Substrate holder

(4) Pressure

(5) Microwave source unit

(6) Gas supply unit

43

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(1) Microwave cavity
The side view of the microwave cavity, the base plate, the substrate
holder and the deposition chamber is shown in Figure 3-3. The diameter of

the aluminum cylindrical microwave cavity was fixed at 17.78 cm and its

height defined by Ls in Figure 3-3 was changeable to tune the microwave

cavity. The cylindrical quartz dome inside the microwave cavity had
dimensions of 5 inch diameter and 3.5 inch height. The microwave cavity
was essentially a termination to the microwave transmission waveguide.
The intensified microwave energy produced the plasma of the feed gases

in a quartz dome inside the cavity. The cavity was designed to operate in

the electromagnetic mode designated TM013. This mode was found to

provide optimum film deposition uniformity. The resonant condition of the
cavity was mainly determined by the position of the cavity short and the
microwave coupling probe. The short was the electrical top of the cavity

and determined the overall length of the cavity, which in turn controlled the

operating mode of the cavity. The position of the probe, defined by Lp in

Figure 3-3, determined the electromagnetic fields near the cavity wall and
hence the coupling of the energy into the cavity. By tuning the positions of
the short and probe, the impedance of the plasma discharge/microwave
cavity was matched to that of the transmission waveguide, producing a
resonant condition. A well tuned cavity would show little or no reflected

microwave power.

45

 

- _ Ca'
l Pyrometer F—_ V'ty

Probe

T Waveguide

 

 

 

 

 

 

 

Microwave

 

 

Base Plate l

 

 

Pressure
Gauge

 

I—

 

 

 

Valve

 

Roughing Pump J

 

 

Microwave
Generator

 

 

 

DC Power
Supply

 

 

"1 Gas inlet

Deposition Chamber

Figure 3-2: Schematic diagram of MPCVD system.

46

 

 

   
    
 
    
 

Sliding Short

Quartz Belljar
Plasma

Base Plate

Substrate
Holder

  

Cooling Water

  

Figure 3-3: The side view of the microwave cavity, the baseplate,
and the deposition chamber of the system.

47

The power supplied to the cavity should be increased to the desired power
level only after the cavity operation in the desired mode has been verified.
Water was used to cool the cavity walls, sliding short, coupling probe, and
base plate. The jet pump (Model 9K862A, Dayton motors) was used to
increase the inlet pressure. The thermocouples (Type K, Omega
Engineering, Inc.) were used to monitor the temperature of the microwave

cavity, base plate, quartz dome, short, and probe.

(2) Process chamber

The process reactor consisted of a 17 inch high, 18 inch O.D.
stainless steel chamber. The sample can be loaded and unloaded through a
10 inch front door. The sample stage attached to the base plate by sliding
through two guiding rods. Cooling water of the sample stage, vacuum
gauges, and electrical feedthrough were assembled through 2.75 inch Del-

Seal ports.

(3) Substrate Holder

Graphite or molybdenum was used as a substrate holder and
accommodates 4 inch substrate. The substrate holder had active cooling,
so the temperature of the substrate was decreasing with cooling. The
substrate temperature was observed by the infrared thermometer (Model

083707, Omega Engineering, Inc.).

48

(4) Pressure

Three capacitance manometers (Type 622A, MKS Instruments, Inc.)
were used to measure the pressure in the chamber. The pressure controller
(Type 651, MKS Instruments, Inc.) read the pressure transducer and
controls the throttle valve (Type 653, MKS Instruments, Inc.) to achieve the

desired deposition pressure. A base pressure of 10 mTorr was achieved

with the mechanical pump (Model SD-300, Varian Inc.). N2 was used to

purge and backfill the chamber.

(5) Microwave source unit

The microwave source unit consisted of a DC power supply (Model
GMP60KSM, Sairem), a microwave power controller (Model PIL408, Sairem)
and a magnetron (Model GMP60KSM, Sairem). A DC power supply drove a
magnetron source producing waves with frequency 2.45 GHz. The power
supply was able to deliver power between 0.6 to 6 kW. The microwave
power circulated from the magnetron source to the plasma, but diverted
the reflected power to the matched load where it was absorbed. Hence, the
magnetron head was protected against any reflected power on the

transmission line.

(6) Gas supply unit

49

The reacting gases were ultra high pure grades (99.999% purity). The
gas supply unit consisted of four mass flow controllers (Type 1159B, MKS
Instruments, Inc.) and a flow readout unit (Model 2470, MKS Instruments,
Inc.) to control the flow of the processing gases. Source gases were mixed

before reaching the inlet on the baseplate.

3.3 CVD Diamond Technology

The fabrication of CVD diamond is categorized into nucleation,
patterning, and doping. The technologies used and developed for the study

are investigated in detail.

3.3.1 Nucleation

Diamond has been shown to nucleate on a wide variety of materials.
Due to the low nucleation density on non-diamond materials, the
substrates are treated to enhance the nucleation density. The commonly
used pro-treatment techniques are abrading [156,157], ultrasonic
nucleation [158,159], bias enhanced nucleation (BEN) [160,161], and
electrophoresis [162]. Diamond powder loaded fluids with different carrier
fluids, diamond particle sizes, and densities are used to enhance the
nucleation density for this study. The details of diamond particle loaded
fluids are summarized in Table 3-1. N10 and DW (DuPont industrial
diamond) are diamond particles dispersed in mainly water and suspending

agent

50

Table 3-1:

Details of diamond powder loaded fluid

 

 

N10 DW DPR
Carrier Fluid Water Water Photoresist
Mean Powder 10 nm 38 nm 100 nm

Size

Density 250 carats/liter 40 carats/liter 12 carats/liter
Nucleation 11 -2 10 -2 8 -2
Density ~10 cm ~10 cm ~10 cm
Application . Spray, spin or .

Method B'usmng brushing 39'"

 

51

 

Figure 3-4: Diamond nucleated by brush-coating of N10.

52

 

Figure 3-5: DW spin coating; (a) spin/growth,
(b) spin/growth/spinlgrowth, Iandl
(c, d) 'r-l-ylvii .. v" w -3 VIIIII-
The sample is spun at 2500 rpm rfor 20 sec,
followed by 5 min growth.

53

 

Figure 3-6: DW coated SI structures.

54

N10 and DW provided high nucleation densities resulting continuous film
in a short growth time. Although the nucleation density was high, diamond
film seeded by brush-coating of N10 exhibited diamond particle
constellations as shown in Figure 3-4. This may be due to the applying
method and the ultra high density of diamond particles in the fluid. DW was
spin-coated in order to reduce the agglomeration of particles. Figure 3-5(a)
shows diamond film after growth for 5 min at 800 C. No pinholes were
observed after the seeding and growth sequence was repeated three times
as seen in Figures 3-5(c) and (d). DPR was prepared by suspending fine

diamond particles with a mean size of 0.1 pm into photoresist [163]. The
uniform nucleation density of 108 cm.2 was achieved. The advantages of

DPR method include simplicity of application, compatibility with standard

IC fabrication process, and reproducibility.

3.3.2 Patterning

Various patterning techniques have been developed to fulfill the
need of desirable structures in microelectronics and microsensor
applications. Patterning of diamond is obtained through either selective
deposition or selective etching.

The selective deposition is achieved by pre-deposition nucleation on
the desired area, or by masking the undesirable area during the diamond

deposition. Ar sputtering in undesired regions was used to suppress

55

nucleation after the substrate was pretreated by ultrasonic method [164].

ZnO, amorphorous silicon, SiOg, and Si3N4 were used as a sacrificial layer

for lift-off process to generate diamond patterns [165,166].

Reactive ion etching (RIE) [167], ion-beam-assisted diamond etching
[168], bias-assisted etching [169,170], electron cyclotron resonance (ECR)
plasma etching [171], and plasma enhanced etching [172,173,174] of
chemical vapor deposition (CVD) diamond films in various gas mixture and
different temperatures has been investigated. The etch rates varied widely
from 6 to 300 nm per minute, depending on the process conditions.
Excimer-Iaser etching and patterning of diamond was performed in the
direct writing mode [175]. Graphitic layer was generated in the process of
etching. Etch rate of 0.2 urn/pulse was achieved. Diamond etching was
observed by exposing to oxygen plasma at the substrate temperature of
less than 100 C using a Ni mask [176].

Most of the techniques either caused damages on the substrate
surfaces or produced undesirable byproducts. Non-destructive and IC
compatible patterning process has been developed at Michigan State
University. DPFi patterning technique and direct patterning system are

descfibed.

3.3.2.1 Photolithographic Method

The standard photolithography process can be employed in DPR

patterning since DPR is photoresist mixed with diamond particles.

56

 

Si

 

 

 

* DPFi spin-coating

   

"25.45551 5535221: '45" 7513135 58
Si

 

* Patterning by lithography

ml

* Evaporation of PR

~11

* Diamond deposition

 

 

 

Si

1 “E ‘3

 

 

Figure 3-7: Schematic diagram of DPR patterning process.

57

The schematic diagram of DPR patterning procedure is shown in Figure 3-7.
DPR was spin-coated on Si wafer at a spin speed of 3000 rpm for 30 sec,
which gave 1pm thick layer, and patterned by photolithography (Model
MJB3, Karl Suss). A 200 W mercury short-arc lamp was used. Primary
exposure wavelengths were 350 — 500 nm. The aligner performed
exposures in a soft contact mode. The carrier fluid was evaporated at the
initial stage leaving behind diamond particles which acted as seeds for

diamond growth.

3.3.2.2 Direct Patterning Method

Two methods are explored; a locally built direct patterning system

and a commercially available printer modified to print seeding patterns.

1:0 Direct patterning system

The direct patterning system was constructed and evaluated its
performance. The block diagram of the system and the picture of substrate
stages and nozzle are depicted in Figures 3-8 and 3-9. The system
consisted of a computer controlled stage, flow controller unit, temperature
controller unit, and a nozzle in a stainless steel vacuum chamber. The
components that placed in the vacuum chamber were prepared to be

vacuum compatible to minimize the contamination.

(1) Motion stage

58

 

Compressed

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

air
* Vacuum
chamber
Fluid Flow
reservoir I controller
Nozzle
Computer _> Temperature §’
controller \ v 7,
\l.’ fx'l
Substrate __
holder XY-stage
Stage
‘ controller .—
Rotary
pump

 

 

 

Figure 3-8: Schematic diagram of the direct patterning system.

59

Diamond Fluid Actuating air input

       
   

Nozzle Nozzle air input

Thermocouple Substrate

Substrate Holder Thermal
insulator

Figure 3-9: Substrate stage and nozzle.

60

Three manipulating stages (Model ATS-100, Aerotech, Inc.) with a linear
resolution of 1 pm and a travel length of 100 mm for substrate and 50 mm
for nozzle along with motion controller (Model U12R, Aerotech, Inc.) were
used to control the positions of the substrate and the nozzle. The motion
controller was interfaced with a computer via lEEE-488 interface. The
cables coming from each of the three motion stages were connected to the
motion controller via the 20-pin feedthroughs (Model lF20-275, MDC
Vacuum, Inc.) with in-vacuum ribbon socket (Model DGCD-10, MDC
Vacuum, Inc.). A ceramic disk spacer (Model 0820-2, MDC Vacuum, Inc.)

was attached to the feedthrough to avoid accidental shorting of the pins.

(2) Flow controller unit

Compressed nitrogen was regulated into three different pressure
regimes. The nozzle was triggered by an input gas with an optimal
operation pressure of 70 - 90 psi. The pressure of atomizing gas for a spray
nozzle was in the range of 15 - 20 psi. The nitrogen pressure of 4 psi was
used to pressurize the diamond fluid. A solenoid valve (Honeywell)
controlled the on/off of compressed nitrogen, thus determined the open
time of the nozzle. The solenoid valve was interfaced with a computer via
an electrical solid state relay through RS-232. The fluid from reservoir
flowed to the nozzle via fluid feedthrough (Model LF—275, MDC Vacuum,
Inc.). The schematic diagram of flow controller unit is shown in Figure 3-

10(a).

61

(3) Temperature controller unit
Four round tubular heaters with single end terminals (Omega Engineering,
Inc.) were inserted into the stainless steel substrate holder to achieve
uniform heating over the sample area. The temperature controller (Model
CN371-KCZ, Omega Engineering, Inc.) was utilized to maintain a constant
substrate temperature during seeding. A thermocouple (Type K, Omega
Engineering, Inc.) connected to the temperature controller monitored the
substrate temperature. A 0.5 inch thick thermal insulating material was
inserted between the heating plate and the motion stages. The schematic

diagram of temperature controller unit is given in Figure 3—10(b).

(4) Nozzle

Two different nozzles, needle valve (Model 740V-SS, EFD)and spray
valve (Model 7808-88, EFD), were evaluated to study diamond nucleation
and patterning. The detail specifications of the nozzles were shown in
Figures 3-11 and 3-12. The amount of fluid that flows was determined by
the valve open time, fluid pressure, flow control adjustment, dispense tip
output size, and fluid viscosity. During operation of a needle valve,
controlled pulsed air acted on the position to withdraw the needle a preset
distance from the needle seat providing fluid flow. The stainless steel shut
off needle seat in the hub of dispensing tip so that fluid cutoff is as close

as possible to the dispensing orifice.

62

(a)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Regulators .
Compressed ' FlUId
air reservoir
Actuating l
Solenoid all‘lnput’ Nozzle
valve Y Atomizing
Solenoid air input
I valve *
Relay I
Relay
Computer
(b)
Temperature ‘— Thermocouple
controller
t Heater
Relay ,_> Powersupply /

 

 

 

 

 

 

Figure 3-10: Block diagrams of (a) flow controller unit and (b)

temperature controller unit.

63

 

 

 

Stroke Control
Stroke Reference

Piston Spring

    

Cylinder Body
Actuat’ng

Air Input Piston and Needle

Mounting Hole
114-28 UNF

Packing Spring
Needle Packings
Fluid Chamber

Fluid inlet
1/8 NPT

 

Needle Seat

lip Adapter

Figure 3-11: Detail specification of needle valve.

Stroke Control
Stroke Reference

Piston Spring

     
     
 

A ctuating CylinderBody

Air Input

10-32 UNF Piston and Neede
Mounting Hole
III-28 UNF
Packing Spring
Needle Packi s
Nozzle "9
Air Input

ill-32 UNF Fluid Chamber

Fluid Inlet
1/8 NPT

 

Air Cap Retainer
Nozzle

Air Cap

Figure 3-12: Detail specification of spray valve.

65

A spray valve provided round patterns with diameters ranging from 3/16 to
3 inches (4.8 to 76.2 mm). The combination of adjustable fluid flow,
adjustable nozzle air, and post-air cutoff provided spray control. Actuating
input air pressure acted on the piston that retracted the stainless steel
precision needle from the nozzle, allowing liquid to flow. Simultaneously,
atomizing air flowed around the nozzle, dispersing the liquid into fine

droplets.

0:0 Direct patterning

The substrate was heated at 75 C so that the carrier fluid
evaporated when it landed on the substrate surface. Figure 3-13 shows
diamond patterns on 4 inch wafers by the direct patterning system. There
was about a fraction of second of delay on the response of solid state relay
and solenoid valve, which resulted of dispensing more fluids than
programmed. The dot size was determined by the amount of the fluid. 330
pm wide line was achieved by DW using a 125 pm opening needle tip as
shown in Figure 3-14. The line width could be controlled by the speed of
the motion stage. The faster the stage moves, the thinner the line gets. The
circles of diameter of 1 cm were drawn by DPR with the same size needle
tip. DPR patterns expanded on the Si surface. DW coating by spray nozzle
did not cover uniformly over the substrate as seen in Figure 3-15(a). The

size of droplets was in the range of less than a micron to 30 microns.

66

 

Figure 3-13: Diamond patterns on 4 Inch substrate using direct
patterning system.

67

.4... , 410.1%: «suave»?

 

Figure 3-14: Diamond patterns by needle valve.

68

 

Figure 3-15: Diamond coated by spray nozzle.

69

 

(b)

 

Figure 3-16: Line patterns by spray nozzle.

70

 

Figure 3-17: Diamond patterns generated by printer.

71

Big droplets exhibited circular shape with more particles along the
perimeter. This was caused by the surface tension of carrier fluid. The
atomizing air controlled the size of the liquid droplets. Figure 3-15(b) shows
the diamond film coated by spray nozzle with optimized conditions. The
roughness of the film still needs to be improved. Figure 3-16(a) shows a 5
mm line obtained by spray nozzle. The line is not well defined. The 400 and
600 pm lines in Figure 3-16(b) were obtained by spraying fluid through a
shadow mask that was in contact with a substrate. The edges of the lines
were not straight because the fluid was able to penetrate under the mask

by the high atomizing air pressure.

0:0 Printed Seeding Pattern

The ink jet printer (Model Stylus 060, Epson) was investigated to
produce diamond seeding patterns. A cartridge was filled with DW. The
patterns on the Si substrate shrank because of the surface tension of the
fluid, and left small dots along side of the main patterns as shown in Figure

3-17. Patterns can be enhanced by a printer with better resolution.

3.3.3 Doping

Boron has shown to be an acceptor in diamond. Boron acceptor
level lies 0.37 eV above the valence band. Although doping in diamond may
be accomplished during deposition, diffusion, or ion implantation, there are

some difficulties with diffusion doping and ion implantation. Diffusion

72

doping of diamond is difficult because of the low diffusivity in diamond
[177]. The diffusion of boron into diamond was achieved [178]. However,
the penetration depth of boron was only 50 nm. The boron diffusion
coefficient in diamond is 100 times smaller than the one in Si. Ion
implantation is also difficult because of residual damage to the diamond
[179]. If the damage exceeds a critical threshold, then a subsequent anneal
will produce graphite. Reliable boron doping in diamond has been
successfully accomplished through in situ doping during deposition
[180,181].

The resistivity of diamond decreased as the average grain size of the
diamond films decreased [182,183]. It was found that heavy doping was

deleterious in the early stage of diamond growth, but did not degrade

growth on an existing high quality diamond [184]. Trimethylboron [B(CH3)3,

TMB] was used as boron doping source of diamond films, which was less

toxic than B2H5. TMB is in the vapor state at room temperature, and is

easily diluted by argon, helium, hydrogen, nitrogen, and silane gases.

In this study, doping of diamond was carried out by 0.1% TMB

diluted in H2 by MPCVD. The resistivity was measured from four point
probes (Model S-301, Signatone) with a probe separation of 62.5 mils. The
resistivity values were averaged over a number of measurements. All

measurements were performed at room temperature. Figure 3-18 illustrates

the change of resistivity as a function of TMB flow.

73

 

 

Resistivity (Ohm-cm)

100 —

10

0.1

0.01

0.001

I

 

 

l i i

0 0.2 0.4 0.6
TMB flow (sccm)

l

0.8

 

Figure 3-18: Resistivity versus TMB flow.

74

 

 

 

Resistivity (Ohm-cm)

1000 *

 

 

 

 

 

 

 

 

 

100 ‘ +4000
+600C
1O — +800C
1 l
0.1 ~
0.01 - :0
0.001 I l 1
0 5 10 15
TMB flow (sccm)

 

Figure 3-19: The growth temperature dependence of resistivity.

75

 

B-doped diamond was deposited on undoped diamond at 800 C for 2 hours

with 1.5% CH4. The resistivity decreased as TMB flow increased and

reached about 0.01 52cm. The resistivity changes by nearly four orders of
magnitude. Although the conduction is mainly due to the boron doping, the
segregation of boron and graphitic phase formed in grain boundaries may
also attribute to the reduction of resistivity. The resistivity of the films
measured as a function of deposition temperature for various doping level
is shown in Figure 3-19. As expected, the resistivity was higher with
decreasing of growth temperature. The impurities and defects incorporated
in the films deposited at low temperature may contribute in the conduction
as the quality of CVD diamond degrades with decreasing substrate

temperatures.

3.3.4 Characterization

A careful characterization is necessary to control and enhance the
quality and properties of the diamond films deposited by CVD. Raman
spectroscopy, scanning electron microscopy, and atomic force microscopy

as characterization tools are described in detail.

. Raman spectroscopy
The Raman spectroscopy is widely used in the analysis of materials,

and the identification of trace elements [192,193]. The wavenumber shift of

1332 corresponds to sp3 diamond peak. The Raman system (R-2001, Ocean

76

Optics, Inc.) consists of a diode laser, a focused probe, a CCD-array
spectrometer, an analog-to-digital converter, and operating software. The

532 nm green laser with a power of 50 mW is used. The optical resolution is

~15 cm'1. The focused probe consists of 90 um excitation fiber and 200 pm

collection fiber. The focal length of the probe is 5 mm.

. Scanning electron microscopy (SEM)

The SEM consists of an electron gun (LaBe) in a vacuum chamber

column and images by collecting the secondary electrons emitted from
samples due to the incident electron beam [194]. It has a large depth of
field which can be up to four hundred times greater than that of a light
microscope. It is widely utilized to inspect the surface morphology, crystal
orientation, the grain sizes, nucleation density, and film thickness. The
need for a conducting specimen somewhat limits its utility for undoped
films. The environmental SEM (ESEM) is developed to overcome the
disadvantage. ESEM maintains the sample chamber in a near-atmospheric
environment more conductive to examination of wet samples and non-
conducting samples, and has a completely different environment, high

vacuum, in the remainder of the column.

0 Atomic force microscopy (AFM)
The AFM is another useful tool for studying the nucleation density,

crystal structure, and surface morphology of films. A very fine tip, mounted

77

on a cantilever, is scanned through the sample to obtain the surface profile.
The advantages of AFM are high resolution and great sensitivity to define
profile differences of vertical variations in the sample [196]. In addition, no
vacuum is needed for the operation of AFM, and it can be used on non-

conducting surfaces.

3.4 Carbon Nanotube Technology

In the present study, we make use of the many control parameters
accessible in an MPCVD reactor to selectively grow nanotubes with
particular morphologies and orientations. Similar to all other nanotube
synthesis techniques, incorporation of defects cannot be avoided during
the growth. A post-growth cleaning process is usually required before

using the nanotubes in device structures.

3.4.1 Catalyst/Patterning

Iron, nickel, and cobalt were commonly used as catalysts for carbon
nanotube growth [185,186,187]. For this study, iron (Fe) or nickel (Ni) was
used as transition metal catalysts on titanium (30 nm) coated Si substrates.

A thin film of Ni or Fe (100 nm) was sputter deposited. Ferric nitrate

(Fe(N03)3) as iron source was dissolved in methanol, Fe coating was

applied by dipping the substrate into the Fe solution. The patterning of

carbon nanotubes was achieved by growing tubes on patterned catalyst.

78

3.4.2 Growth Study

Various shapes of carbon nanotube growth were obtained by varying

synthesis conditions. Purification process is discussed.

3.4.2.1 Growth

The flexibility of the MPCVD system, which permits a modification of
plasma shape through tuning of the cavity, allows synthesizing a wide
variety of carbon allotropes, ranging from nano-diamond [188] to
nanotubes. Nanotubes were fabricated by MPCVD. Typical parameters

varied in this study were growth temperature (450 - 900 C), growth time (0.5
- 120 min), atmosphere (N2/H2/CH4), and pre- (NZ/H2) and post-growth

treatment. An overview of nanotube structures grown under varying
deposition parameters is summarized in Table 3-2. There was no
appreciable nanotube growth below 600 C. For growth temperatures in the
range of 800 - 900 C, etching of carbon nanotubes was observed. A very
uniform growth was achieved at temperatures between 650 C and 750 C. As
shown in Figure 3-20(a), clusters were formed on top of the nanotubes
during deposition at 650 C. The diameters of tubes grown under these
conditions were in the range of 20—100 nm, implying multi-wall nanotubes.
Energy-dispersive spectroscopy (EDS) indicated the presence of carbon in
these clusters, as shown in Figure 3-21. A gold peak was due to the thin Au

coating on the sample to improve the resolution of the image in SEM.

79

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- ‘x. ‘ ’ _ ' ‘ . ~-
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- ,\ .
a ‘ - ~
( - . -
.. .

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| i O

(b)

 

Figure 3-20: Carbon nanotubes grown for 15 min at (a) 650 C
and (b) 7500.

82

UJd’JF—‘Cif‘i

9L1

 

 

 

O . 000 ke‘u’

Figure 3-21: Energy dispersive spectroscopy of clusters
deposited on carbon nanotubes.

83

 
   
 
  

(a) .-:-:3:123:3:37"""""""3:3:3:- -----
.:.:.:.:.:.:.:.:. Plasma :.:.:.:.:.:.-

..................... Si Wafer
Fe layer

................................
................................
................................

HHHlIHIEHH

100 pm
thick metal
wire

 

Figure 3-22: (0) Schematic diagram of growth setup and
(b,c,d,e) spiral growth of carbon nanotubes.

 

Figure 3-23: Carbon nanotubes grown for (a) 30 sec and (b)
120 min.

85

 

Figure 3-24: Carbon nanotubes grown for 10 min with (a) 2%
and (b) 8% CH4 In H2 and N2.

86

 

(a,b) Lateral growth and (c,d) vertical growth of

Carbon nanotubes.

Figure 3-25

87

 

Figure 3-26: Carbon nanotubes grown for 15 min at 650 C on
(a) Fe and (b) Ni coated substrates.

88

Increasing the deposition temperature to 750 C reduced the size of these
clusters, but increased the diameter of the tubes to 100—400 nm as shown
in Figure 3-20(b). We interpreted this diameter increase by improved
growth kinetics at higher temperatures, in agreement with other study
[189]. The build-up of clusters was strongly suppressed if nanotubes were
grown by placing the Fe-coated substrate upside down, leaving a gap
between the growing surface and the substrate holder. In this case, tubes
were grown downward and the plasma has to reach the growing surface.
The processing pressure and applied microwave power were 32 Torr and
1650 Watts, respectively. Spiral growth of nanotubes was observed with
100 um separation as shown in Figure 3-22. At the growth temperature of
650 C, the tube lengths were found to increase from approximately 1 pm to
over 100 pm if the growth time was increased from 30 sec to 120 min, as
seen in Figure 3-23. The tube diameter was not affected by the growth time.
Also in this case, terminating clusters can be clearly seen. Figure 3-24
shows that methane concentration certainly affects the growth rate. Both
vertical and horizontal growth of nanotubes was observed. A pro-growth
treatment of Fe catalyst in nitrogen plasma enhanced vertical growth as
shown in Figure 3-25. The effect of Fe and Ni as a catalyst was
investigated, while keeping the growth parameters the same. Although the
growth on Fe or Ni yielded similar ranges of diameters, density and

orientation (vertical or horizontal), the growth rate was faster for Fe than

89

that for Ni, consistent with the higher catalytic activity of Fe. Morphology of
nanotube films grown on Fe and Ni is shown in Figure 3-26.

Different nanotube shapes were obtained when the substrate was
etched by a mixture of sulfuric acid (1 part) and hydrogen peroxide (1part)
for a minute before applying the Fe coating. This treatment lead to
“macaroni” shapes with a hollow core, which appeared to be woven out of
very fine nanotubes, as seen in Figure 3-27. This technique has the
potential of creating different types of "fibers“ made of nanotubes.

Transmission electron microscopy (T EM) was used for accurate
measurements of the tube diameter. As seen in Figure 3-28, TEM images of
nanotubes grown at 650 C showed two distinct features, namely a straight
hollow and a repeating arrowhead shape. For straight hollow tubes, the
width of hollow region was in the range of 11—55 nm, with a wall thickness
in the range of 20-38 nm depending on the tube diameter. The tip of the
arrowhead was in the range of 8-12 nm, while the wide side of arrowhead
was in the range of 15-30 nm. It is interesting to know that the average tube
diameter was different from the hollow structures. The tubes with a straight
hollow core were about 20 nm larger in diameter than the ones with an
arrowhead shape. The tip of the tubes was tapered and closed. The black
spots on the walls seemed to be the structural defects generated during

growth. As shown in Figure 3-29 and Figure 3-30, patterned substrates

such as a gear and 250 x 250 um2 square were used to deposit nanotubes

selectively.

9O

 

Figure 3-27: Macaroni shape of carbon nanotubes.

91

 

Figure 3-28: TEM micrographs of carbon nanotubes.

92

 

Gear patterned carbon nanotubes.

Figure 3-29

93

‘A.

é: ,
<-
1,:

J
1
p
k‘
I

 

Figure 3-30: Square patterned carbon nanotubes.

94

 

Figure 3-31: (a) As-grown carbon nanotubes and (b) carbon
nanotubes subjected to ultrasonic treatment.

95

The substrate was treated in H2/N2 plasma at 650 C for 5 minutes, followed

by exposure to CH4. The growth lasted for 15 min. SEM observations

indicated that carbon nanotubes were also grown outside of the patterned
area, as seen in Figure 3-29. This might be caused by that titanium on the
substrate, which enhanced the adhesion of iron particles, was not
completely etched away. The alignment and orientation of nanotubes in

Figure 3-30 were uniform across the deposited area.

3.4.2.2 Purification

Previously reported purification methods [190,191], designed to
remove clusters and other undesirable structures from the nanotube
material, involved laborious steps such as refluxing, centrifugation,
sedimentation and filtration, or boiling in an acid bath. An alternate, less
laborious way to purify CVD grown nanotubes was demonstrated in this
study. It involves treatment of as-grown nanotubes in methanol in an ultra-
sonic bath for 15 min. Tubes cleaned in this way, shown in Figure 3-31,
became free of the cluster residue. CVD grown nanotubes adhered well to

the substrate, thus suggesting their application as field electron emitters.

3.4.3 Characterization
Carbon nanotubes exhibited two Raman peaks at 1350 and 1580 cm'1.

The growth orientation, diameter, length, and density of tubes were

96

inspected by SEM. In addition to Raman spectroscopy and SEM as
described in section 3.3.4, TEM was utilized to characterize the carbon

nanotubes.

. Transmission electron microscopy (T EM)

The TEM produces a transmitted electron image of a thin specimen,
magnified from 100 to approximately 500000 times, and with a resolving
power of approximately 0.2 nm [195]. To produce the standard bright-field
TEM image, the electron beam must be able to penetrate the sample. A TEM
is used to obtain high-resolution images of fine internal structures of

carbon nanotubes.

3.5 Summary

MPCVD was employed to fabricate poly-diamond and carbon
nanotube films. Diamond was nucleated by different particle densities and
particle sizes. The patterning of diamond was performed by
photolithography and direct patterning system. The direct patterning
system was constructed and evaluated its capability. The uniform coating
and 330 um line was obtained. The conventional printer was tested for
diamond patterning. The resistivity was achieved in the range of 0.001 —
450 52cm using TMB as boron doping source. High density of carbon
nanotubes with different morphologies was synthesized by varying the

deposition conditions in a MPCVD reactor. A cleaning procedure,

97

consisting of ultrasonic treatment of nanotubes in methanol, was found to

efficiently remove any amorphous residue formed during the synthesis.

98

CHAPTER 4

FIELD EMISSION CHARACTERIZATION

4.1 Introduction

The detail of the field emission characterization system is described.
The field emission and field emission mapping studies from poly-diamond

and carbon nanotube are discussed.

4.2 Field Emission Characterization System

The field emission characterization system was designed and built
locally. It consists of vacuum chamber, pumps, pressure gauges and
readouts, power supply, measurement instruments, and computer
controlled xyz-stages. The schematic of the system is shown in Figure 4-1.

The system can be categorized into the following subsystems.

(1) Chamber

(2) Vacuum system
(3) Pressure

(4) Motion stage

(5) Measurement setup

99

Viewport Microscope
/ / Illuminator

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

::|
Microscope N ,
holder —/ r 1 Baratron vacuum
' ’ ‘ gauges (1000
Hot cathode - g Torr, 2Torr) 7
ion gauge H: ~ Rough vacuum
gauge
xyz-stage .
& probe ‘ .
assembly L /— Illummator holder
Chamber :
support _/ Substage .
frame
% —
Vacuum chamber Data acquisition
via IEEE488
[ ] _- Voltage supply
Turbo pump ""— Multimeter
Foreline trap
Controller I Mechanical
pump

 

 

 

 

Figure 4-1: Setup of field emission characterization system.

100

(1) Chamber

The height and inner diameter of the vacuum chamber were 26
inches and 15 inches, respectively. There was a glass view port attached to
the top plate which allows monitoring of the sample setup inside the
chamber from above. This was accomplished by an optical microscope
(Model Stereo Zoom 5, Bausch & Lomb) with a magnification of 10x
attached to a custom built microscope holder. Sample illumination through
the viewport was accomplished via a fiberoptic illuminator (Model 1177E,

Reichert Jung).

(2) Vacuum system

The chamber was connected to a turbopump (T PU33O with TCP300
controller, Balzers) with a rotary vane backing pump (Model 5KC49ZG1412,
General Electrics). The mechanical pump can be shut off by means of an

inline valve in the forevacuum connection.

(3) Pressure

The pressure inside the system was monitored by a Baratron gauge
(Type 122A, MKS) from atmospheric pressure down to 1 Torr, and a
thermocouple gauge (Type DC-3M, MDC) for rough vacuum pressures from
1000 mTorr to 1 mTorr. Then a hot cathode ion gauge was switched on

(IMR132 gauge head and IMG07O ion gauge controller, Balzers).

101

 

 

J Probe (anode)
I Sample contact (cathode)

 

 
 

 

Power supply

 

 

xyz-stage

vacuum chamber R1 ‘ ...... .

 

 

 

 

R2

 

Stand alone
xyz-stage
controller

 

 

 

 

 

——‘

| l

 

 

 

 

 

 

 

 

l |

- Host computer with IEEE488 interface
- Data acquisition and graphic/file output
- Measurement process control

Figure 4-2: Electrical setup for field emission measurement.

102

The desired final pressure was below 10’7 Torr. The Baratron gauge, the

thermocouple gauge, and the nitrogen venting valve could be shut off from

the rest of the system by means of an inline valve (IV-150M, MDC).

(4) Motion stage

Inside the chamber a computer controlled xyz-stage (CTC-290-3,
DynaOptic motion) made of AI with a travel range of 50 mm in each
direction and a precision of 1 um was mounted onto a custom built
substage which allowed coarse and find adjustment. The 6-line flat cables
coming from each of the three stage motors were connected to the inside
contacts of the 20-pin feedthrough with screw-on inline barrels. The z-stage
was mounted separately from the xy-stage. The probe tip (Signatone) was
screwed to a brass probe holder with insulating Teflon intermediate layer.
The insulation was required because the xyz-stage, the substage, and the
chamber walls were all connected electrically conductive. The probe holder
fitted into a manufactured stainless steel adapter that was screwed into
threaded holes in the z-stage. It protruded horizontally over the xy-stage
where the sample was mounted on an insulating ceramic plate and
clamped to the stage surface by means of Teflon clamps. Several holes
spread over the xy-stage allowed samples of different size or even multiple

samples to be mounted.

(5) Measurement setup

103

The setup for the electrical measurements performed is given in
Figure 4-2. The emission current was measured indirectly by measuring the
voltage drop across the resistor R1 by nano-voltmeter (Model 181, Keithley).
The resistor R2 which was at least ten times higher in value serves as
security resistor for the case of arc breakdown. The voltage supply (Model
248 High Voltage Supply, Keithley) allowed for do voltages from 20 V to

5000 V.

4.3 Field Emission/Mapping Study

The field emission and field emission mapping from CVD diamond
and carbon nanotube films are studied using the computer controlled

system described in section 4.2.

4.3.1 CVD Diamond

Diamond films were deposited by a chemical vapor deposition
system. A metal plate anode was used to measure the current density over
the emitting surface and a pointed tungsten tip was used for mapping the

emission current and emission site density.

4.3.1.1 Field emission
The reported emission current densities was typically below 1 A/cm2, and

was affected by diamond deposition parameters [66] and non-uniformity of

emission sites [197]. While the presence of grain boundaries and/or defects in

104

diamond seemed to be necessary for appreciable field emission, it was not clear

whether the non-uniformity of emission sites was related to variation in defect
densities, diamond quality (spa/sp2 ratio), electron affinity, grain size or grain-tip
height. A study of the effect of film deposition parameters showed that low

spa/3p2 ratio, ion-implanted defects, patterned structures, or low-temperature

diamond lead to higher current densities [29,30,39,45,198,199]. To generate
more data for understanding the non-uniformity of emission sites, it is important
to study the effect of doping, deposition temperature, post treatment and seeding

method on the uniformity of emission sites for poly-diamond films.

. Fabrication
Employing different seeding densities, summarized in Table 3-1, undoped

low-temperature polycrystalline diamond films were synthesized on p-type Si

substrates by MPCVD using 1% CH4 in H2. The temperatures, monitored by an
optical pyrometer, were kept at the 500, 550 and 600 C. Figure 4-3 shows SEM
micrographs for DPR grown at 500, 550 and 600 C for 2 hours. Aluminum was
thermally evaporated on the backside of Si wafer to provide an ohmic contact.
Then, the samples were annealed at 450 C in nitrogen for 30 min using a rapid

thermal processor.

. Field emission study

105

 

Figure 4-3: SEM micrographs of DPR deposited at (a) 500 C,
(b) 550 C, and (c) 600 C for two hours.

Cathode contact

 

Anode contact

 

Si wafer with Al on the backside
Diamond Film

 

 

 

 

Spacer Spacer

 
   

Insulator

 

Figure 4-4: Setup for field emission measurement using
flatanode.

107

Grain densities and electric fields to achieve 1 p.A/cm2 for

 

 

 

Table 4-1:

diamond grown at 600 C.

Final Grain Density Electric field (V/um) for 1 uA/cm2

(cm-2) for 6000 film 5006 5500 6000
DPR 2.5 x 108 22.5 17.5 15.81
DW-b* 4.8 x 109 16.25 16.13 15.69
DW-s* 8.5 x 109 15.63 14.63 14.06
N10 1.6x 101° 15 14.38 13.06

 

* b is brush seeded and s is spray seeded.

108

 

 

2.0E-05 6

+
s

1.5E-05 —

 

 

 

1.0E-05 6

5.0E-06 -

Emission current (A)

 

 

0.0E+OO
1000 1500 2000 2500 3000

Applied Voltage (V)

E

 

 

 

 

Ln(|/V2)

 

'35 l i —I

0.0002 0.0004 0.0006 0.0008
(b) W

 

 

 

 

Figure 4-5: (a) l-V characteristics of diamond grown at 600 C
with different seeding methods and (b) Fowler-
Nordheim plot of N10 film grown at 600 C.

109

 

  
  
 
 
 
 

 

 

 

 

 

 

 

 

 

 

 

2.0E-06 ~—
g +6000
'00:: 1.5E'06 T" +550C
g- +500C
0 1.0E—06 ~—
C
.9
‘3 5 0E-07 —
'E .
Lu

0.0E+OO

1000 1500 2000 2500 3000 3500

(a) Applied Voltage (V)

-23 _

-30 4
6?
S -32 -
5

-34 -

'36 1 1

0.0002 0.0004 0.0006

(b) 1N

 

 

 

Figure 4-6: (a) I-V characteristics of DPR film grown at 500,
550, and 600 C and (b) Fowler-Nordhelm plot of
DPR film grown at 600 C.

110

 

 

For a systematic study of field emission from diamond, diamond films were
deposited at 500, 550 and 600 C on Si wafers seeded under different conditions.
The field emission current versus voltage (l-V) characteristics were measured
using a brass plate anode keeping the spacing between anode to emitter at 160
pm by an insulating spacer as shown in Figure 4-4. Table 4-1 summarizes the
grain density and turn-on electric field by the effects of seeding method. The
grain size was the smallest for the N10 film and the largest for the DPR film.
Thus, the N10 film had the highest grain densities which resulted in the lowest
emission field. The emission varied inversely with grain size.

Figure 4-5 shows the emission current for the 600 C films. The high
emission current for the smaller grain sizes was consistent with earlier results for
doped diamond films prepared by hot filament CVD [66]. Table 4-2 summarizes
the effect of deposition temperatures and Figure 4-6 illustrates the emission
currents for DPR films grown at different temperatures. As all these films were
not intentionally doped, the scattering in the data might be due to emission
instabilities usually observed for high resistivity films. The results in the present
study were opposed to the earlier study [199] that diamond films grown at lower
temperature showed higher current densities. The difference between two works
was that films in the earlier works were continuous, but they were not in this
study. The surface grain densities were slightly decreasing but the grain
boundary densities were increasing with increasing deposition temperature as
shown in Figure 4-3. The graphitic inclusions or enhanced conductivity along

grain boundaries had been suggested to aid the electron emission [6,62,201].

lll

The Fowler-Nordheim plots of N10 and DPR films grown at 600 C were shown in
Figures 4-5(b) and 4-6(b), respectively. The plots yielded approximately straight

lines, which indicated the field emission behavior.

4.3.1.2 Field emission mapping

The electron emission from the surface of CVD polycrystalline
diamond (poly-diamond) had been intensively studied for its application in
field emission displays (FED) [6,201]. The experimentally observed electron
emission from the surface of undoped or p-type polycrystalline diamond
gave a great variance in spatial uniformity which arises from non-
uniformity of emission sites. it was, however, not clear whether this non-
uniformity was related to variation of electron affinity (dependent on
hydrogen passivation of diamond surface), surface roughness (always
present on unpoiished polycrystalline diamond surface), surface defects
(intrinsic or impurity related) or grain size. The deposition parameters,
such as temperature, doping and gas mixture ratio, influenced the film
morphology and defect contents. A clear correlation between emission

properties and material properties could not be established at present.

. Film fabrication
The polycrystalline diamond films were deposited on p-type Si (100)
substrate and free-standing diamond by MPCVD. Substrates were placed

on a graphite substrate holder.

112

Table 4-2: Summary of deposition conditions and field emission current

 

 

 

 

density.
Deposition Parameters Emission
Process Gases ' ° current
Sample (sccm) Temperatur Degoéiéion densit
e C
Hg, TMB + Hg CH4 ( ) (hours) ("A/cm )
M 1 2 7 0 2 .1
S Flows for H2 0 0
M82 and 0.1% 8 700 2 5912
TMB* in H2
M83 are 199 and 1 14 700 2 2.4
sccm for all
M85 samples, 8 600 5 1342
M89 '9599Ct've'y' 8 700 2 5850

 

* TMB: Trimethylboron

113

 

 

2000
E
3 1500
g
1000 - . . , 1
1200 1300 1400 1500 1600
(b) Wavenumber Shitt(1lcm)

 

 

 

 

 

 

 

1 .0E-07 -
1 .0E-08 -
1 .0E-09 -

«0°

\0 0° 220

Current(A)

 
 

 

(c) “"7

 

 

 

Figure 4-7: (a) SEM micrograph, (b) Raman spectra, and (c) field
emission mapping for diamond film deposited at 700 C
with 1% CH4 in H2.

114

 

2000

1500

Intensity

1 000

 

1,

0 | I l
1200 1300 1400 1500 1600
b) Wavenumber Shift(1/cm)

 

 

 

 

 

Current(A)

 

 

 

 

Figure 4-8: (a) SEM micrograph, (b) Raman spectra, and (c) field
emission mapping for diamond film deposited at 700 C

with 4% CH4 In H2.

115

 

1 600

—|
A
O
O

1 200

Intensity

1000

800 I
1200 1300 1400 1500 1600

b) Wavenumber Shift(1/cm)

 

 

 

 

 

 

 

     

 

1.0E-04
A 1.0E—05—/’\
s M
E 1.0E-06‘
9 4
3 1.0E'O7_
1.0E-08-
10509 H ' ,
0 0 0
\0 00 0 250
0 $0 34.00550 100 0
um 06‘
(c)

 

 

 

Figure 4-9: (a) SEM micrograph, (b) Raman spectra, and (c) field
emission mapping for diamond film deposited at 700 C

with 7% CH4 In H2.

116

Substrate temperature was measured by means of infrared pyrometer
(Model 083707, OMEGA), which recorded thermal radiation from the
substrate. Before diamond deposition, the substrate surface was seeded

with diamond particles. DPR was spin-coated on the substrate. A gas

mixture consisting of 0.1% trimethyiboron (TMB) in H2 was used as source

for in-situ of boron. At the end of diamond deposition, samples were
treated in hydrogen atmosphere for 10 minutes at the deposition
temperature.

For a systematic study of field emission from diamond, diamond
films were deposited under different growth conditions. Table 4-2
summarizes the deposition conditions of the films. The first set of films
was deposited at various methane concentrations, while keeping substrate
temperature constant at 7000. The deposition temperature with same
methane concentration was varied for the second set. The third set was
deposited on polished free-standing diamond. The diamond film quality
was monitored by scanning electron microscopy (SEM) and Raman

spectroscopy.

. Field emission study

The film with 1% CH4 in H2, shown in Figure 4-7, displayed well

faceted grains.

117

 

 

2000
5?
W
51500
E
1m| I
1200 1300 1400 1500 1600
(b) Wavenumber Shift(1/cm)

 

 

 

 

 

Emission current(A)

 

 

 

 

Figure 4-10: (a) SEM micrograph, (b) Raman spectra, and (c) field
emission mapping for diamond film deposited at 600 C
with 4% CH4 in H2.

118

The increase of CH4 ratio exhibited degradation in grain facets and

decreased the diamond peak intensity in the Raman spectra as shown in
Figures 4-8 and 4-9. Cauliflower type morphology was usually observed

under the conditions of high carbon saturation on limited surface diffusion

causing extensive renucleation. The film deposited with 4% CH4 exhibited

high densities of microtips and grain boundaries due to the secondary
nucleation, and showed more emission sites and high emission current.
High quality (sample M81) and cauliflower type (sample M83) diamond
films lead to a decrease of the emission current. The emission current

densities for the samples are listed in Table 4-3. The current density for the

film grown at 700 C with 4% CH4 was 5.9 mA/cm2 which was several orders
of magnitude higher than the ones for 1% and 7% CH4 films.
Representative microstructures of films synthesized at 6000 with 4% CH4
conCentration in H2 was shown in Figure 4-10.

Although films deposited at 600 and 700 C with 4% CH4, samples

M82 and M85, showed comparable densities of microtwins and grain

boundaries, Raman peak at 1332 cm.1 was sharper for the 700 0 sample

(M82), indicating a higher quality, than that for the 600 C sample (M85).

119

 

 

 

 

 

 

 

 

 

       

6000

3.5000

§4000

C

- 3000

2000. 1

1200 1300 1400 1500 1600
(a) Wavenurrber Shift(1/cm)
1.0E-05
5: 1.0E-06
C
9
5
c 1.0E-07
.9
(D
.9
E 1.0E-08
LU
1.0E-09
<3
§ ,9° 0 I 000
N '9 0° 7 00
w x 00

b 03
( ) Um 96‘

 

Figure 4-11: (8) Raman spectra and (b) field emission mapping
for free-standing dlamond film.

120

 

 

 

1300 1400 1500
WavermberStiftU/crn)

 

 

16(1)

 

 

Emission current(A)

 

 

 

 

Figure 4-12: (a) SEM micrograph, (b) Raman spectra, and (c) field
emission mapping for free-standing dlamond film

deposited at 700 C with 4% CH4 in H2.

121

 

The fact that the density of emission sites for the 700 C sample (M82) was
high seemed to support the model that high density of grain boundaries in
the vicinity of high quality grains indicated by Fiaman spectra was
important for field emission.

Polished free-standing diamond wafers available commercially were
used to minimize the effect of a geometric field enhancement on the
surface. Figure 4-11 shows that few emission sites were observed from
polished free-standing diamond film. Although the surface of the film was

relatively smooth, the grooves were found after doped diamond growth at

700 C with 4% CH4 for two hours as shown in Figure 4-12. The doped film

(M89) showed higher emission site density than that for undoped free-
standing diamond wafer. High quality diamond without a high density of
grain boundaries showed low emission sites. However, if a film with a high
density of grain boundaries and defects was deposited on top of a high
quality diamond film, the emission was enhanced. it also was found that
the electron emission from poly-diamond could be affected by defects and

field enhancement at the tips [62].

4.3.2 Carbon Nanotubes

Carbon nanotubes were deposited on Si wafer coated with metal
catalyst and pointed metal tips using chemical vapor deposition system.

Field emission characteristics from carbon nanotubes were studied.

122

 

 

4.3.2.1 Carbon Nanotube Film

Carbon nanotubes have been attracting considerable attention because of
their unique properties and potential for use as an electron field emitter. It
is possible to achieve high emission current at moderate extraction
voltages as a result of the high aspect ratio. The field emission properties
of nanotubes with different orientations and after cleaning the residual

particles were studied.

0 Fabflcaflon
Nanotubes were produced by MPCVD system using Fe or Ni as
catalysts on Si wafer. The growth of nanotubes at a temperature of 650 C
using a mixture of methane, hydrogen, and nitrogen lead to nanotubes with

(i) different densities, (ii) horizontal or vertical growth and (iii) diameters in

the range of 20-100 nm. Carbon nanotubes with density of 108—109 cm-2

were deposited uniformly on the substrate.

. Field Emission
The field emission mapping was performed on as-grown nanotube film.
Figure 4-13 shows the non-uniformity of emission site and emission
current which may be due to residual clusters sitting on the films. The

nanotube film was treated in an ultrasonic bath.

123

 

 

 

Emission Current (A)

 

 

Figure 4-13: (a) SEM micrograph and (b) field emission
mapping for carbon nanotube film grown at
650 C.

124

 

 

 

 

Emission Current (A)

 

(C)

 

Figure 4-14: (a,b) SEM micrographs and (c) field emission
mapping for carbon nanotube film of Figure 4-
13 after cleaning.

125

 

 

 

T f

2 4 6
Applied Field (V/um)

 

 

 

 

 

j? ”ll
llgil‘i'l ill
I

Emission Current (A)

“JJl

 

(C)

 

 

 

Figure 4-15: (a) SEM micrograph, (b) l-V characteristics, and (c) field

emission mapping for highly oriented carbon nanotube
film.

126

The emission mapping revealed that electron emission was improved by
removing the clusters in an ultrasonic treatment as shown in Figure 4-14.
Highly oriented nanotube film as seen in Figure 4-15 was studied for field
emission properties.

The site density and uniformity of electron emission from nanotubes
treated in ultrasonic was not as high as vertically oriented nanotubes.
Nanotubes lost its orientation during the ultrasonic process as seen in
Figure 4-14(b). This resulted in different local fields for each emitting sites.
An emission site density was enhanced dramatically and the emission was

uniform over the film surface. By using a flat anode separated by insulating

spacers, current densities of 10 uA/cm2 and 350 uA/cm2 were measured at

2.3 V/um and 4.3 V/um, respectively. The reported turn-on field to produce a
current density of 10 [LA/sz was in the range of 0.75 - 7.7 V/um [2.142-

2.145].

4.3.2.2 Nanotubes on a pointed tip

The use of carbon nanotubes as tips in scanning probe
microscopies had been fascinating since high aspect ratio, mechanical
robustness, and electrical conductivity provide great advantages over
conventional silicon tips [203,204]. Most nanotube probe tips was made by
mechanical attachment of nanotubes to silicon tips by the van der Waals

force or an acrylic glue under optical or electron microscope [205,206,207].

127

 

To overcome the time consuming attaching process, the direct growth of
nanotube on metal catalyzed Si tips by CVD was reported [208,209].
Besides their applications as tips in scanning probe microscopes,
nanotubes were investigated as an electron point source. Recent studies
show that nanotubes provided high currents at relatively low field with
good stability for a long period of time [210,211,212]. The electronic
structure, emission stability, and energy distribution of emitted electrons of
a single nanotube mounted on metal tips was studied to better understand

the field emission mechanism [134,137,213].

. Fabrication

Carbon nanotubes were synthesized on metal tips using CVD
process. Four different sizes of 100 um, 200 pm, 500 um, and 1000 pm of Ni
and Fe wires were used to form a pointed tip. Electrolytic etching was
performed on these wires. The etching setup and etchant are described in
Figure 4-16 and Table 4-3, respectively. Mixtures of water (30 ml), sulfuric
acid (15 ml) and phosphoric acid (70 ml) for Ni wire, and sulfuric acid (60
ml) and water (40 ml) for Fe wire were used for electrolytic etching. The
etching rate was enhanced by heating the solution to around 50 C. DC
voltage (6V) was applied between the anode and the cathode. 500 um wires
were only used for CNT fabrication because of the long etching time for
1000 um and handling for 100 and 200 pm wires. The tip radii of etched

wires were in the range of 0.2 to 3 microns as seen in Figure 4-17.

128

Table 4-3: Etchant for electrolytic etching of nickel and Iron wires.

 

 

Material Etchant Cathode
. 30 ml Di water, 70 ml phosphoric acid, .
N'°"°' 15 ml sulfuric acid N'°"°'
iron 40 ml DI water, 60 ml sulfuric acid Platinum

 

 

 

 

 

 

V 6V dc supply

 

 

 

 

 

 

 

 

 

 

 

 

 

 

w

Metal
cathode

Fe or Ni
Wire Etchant

Figure 4-16: Diagram of electrolytic etching setup.

129

 

Figure 4-17: SEM micrographs of nickel wires after electrolytic
etching. (a) 100 um, (b) 200 pm, (c) 500 pm, and (d)
1000 pm.

130

MPCVD was employed to synthesize carbon nanotubes. The wires were
placed in the holes of a ceramic disk in such a way that they were pointing
towards the plasma as shown in Figure 4-18(a). The processing pressure
and applied microwave power were 22 Torr and 1300 Watts, respectively.
The wires were heated in the mixture of 90 sccm of hydrogen and 10 sccm
of nitrogen for 5 min, then methane was introduced to grow nanotubes. The
flow rate of methane was 6 sccm. The deposition of CNT lasted for 5 min.
The dense plasma was locally formed around the sharp tip of the wire. This
caused an increase of temperature at the tip area and resulted in less
nanotube growth. The etching of CNT at the temperature above 800 C was
observed in earlier experiments [214].

A different configuration of wire placement was used to reduce the
direct exposure of wire to the plasma. An etched Fe or Ni wire was placed
at the center parallel to the substrate holder. The side view and top view
are depicted in Figure 4-18(b) and (c). A silicon wafer supported by 500 um
wires at the two sides was positioned onto the sample wire. The tip of the
wire was located under the Si wafer. 1650 Watts of microwave power and
32 Torr of operation pressure were used to retain the temperature of the
specimen at approximately 650 C. The flow rates of processing gases were
kept the same as the one for the configuration in Figure 4-18(a). The
density of nanotubes was improved with this configuration. The SEM
micrographs of nanotubes grown on Fe and Ni tips were shown in Figures

4-19 and 4-20.

131

 

Wire

 

. I . . Ceramic ——>
Wu

””“lllm ”ll“ «Substrate holder

 

Supporting Wire

(C) (d)

    

t t h l
Subs ra e 0 de Etched Wire

Figure 4-18: Diagrams of wire placement in MPCVD. (a) side view
and (b) top view of configuration 1, (c) side View and
(01) top view of configuration 2.

132

 

Figure 4—19: (a-d) SEM micrographs of nanotubes grown on Fe
tips.

133

 

 

Figure 4-20: (a,b) SEM micrographs of nanotubes grown on Ni
tips.

134

 

Copper supporting rod

  

 

 

lueulerul-z

 

 

XY-manipulator

Cathode

Aluminum (anode)

 
 

insulator

   

 

 

 

Figure 4-21: Measurement setup of field emission
from carbon nanotubes on a pointed tip.

135

 

 

 

 

1 .E-03 -

 

 

 

 

 

 

 

A 1.E-04 —
S,
E 1 E-05 —
g -20
(3 1 E 06 — A
E . E25
i3 1.E-07 — 5'30
LE 35
1-E-08 “ 0 0.001 0.002 0.003
1
1.E-09 . . ' '
O 500 1000' 1500 2000
(D) Applied Voltage (V)

 

Figure 4-22: (a) SEM micrograph and (b) l-V characteristics of
nanotubes grown on Fe tip. The inset is Fowler-
Nordheim plot.

136

 

 

 

 

 

1 .E-04 —

 

 

 

 

 

 

 

E 1 E-05 - fi
‘5
g 1.E-06 a 55::
N ..
“é $-28
.3 1 E'07 _ 5 '30
'3 -32 i . .
UJ 1 5'08 — 0 0.002 0.004
1N
1.E-09 l l i l l
0 '500 1000 1500 2000 2500

Applied Voltage (V)

 

Figure 4-23: (a) SEM micrograph and (b) I-V characteristics of

nanotubes grown on Ni tip. The inset is Fowler-

Nordheim plot.

137

 

 

Figure 4-24: SEM images of nanotube on Fe tip: (a,b) as grown
and (c,d) after field emission measurement at 6.7 [IA

138

The tip had various densities of tubes, ranging from a single tube to

bundles of tubes. The tube diameter was approximately 40 nm, which

indicated multi-walled carbon nanotubes, protruding 2 to 6 pm from the tip.

. Field emission study

The nanotube deposited wire was placed on the copper rod, as
shown in Figure 4-21. An aluminum plate was used as an anode. The
distance between anode and cathode could be adjusted by the vertical
movement of the stage. The separation was measured approximately 100 -
500 pm. There was no appreciable emission current from a metal tip with
typical fields of CNT measurement before nanotube deposition or a
nanotube coated metal tip with reverse bias. The electron emission was
mostly governed by a single nanotube that protruded slightly further than
the other nanotubes. A single nanotube protruded and would experience
an enhanced electric field. The l-V characteristics of nanotubes on Fe and
Ni tips are displayed in Figure 4-22 and 4-23. The saturation current at high
fields as shown in Figure 4-23(b) might be owing to the limited carrier
concentration in a nonmetailic emitter [215]. it was reported that the
electron emission from carbon nanotube was from the localized levels near
the Fermi level, which suggested that the localized states at the nanotube
tips were responsible for the emission [216]. The position of these levels

with respect to the Fermi level depended on the tube chirality, diameter,

139

and the presence of defects [217]. According to Fowler-Nordheim theory,

the current density is given by

- F2 %
J =1.56x10 ‘5—¢—<:xp(-6.83><107 £1?) (4.1)

F is the local field at the emitting surface in V/cm and ¢ is the work function
of the emitter material in eV. The resulting electric field at the emitting
surface can be defined as F = [E ,=,BV/d, where V is the applied potential, d
the distance between cathode and anode, ,Bthe field enhancement factor,
and E: V/d the macroscopic field. A Fowler-Nordheim plot should be linear
if the current was governed by field emission. Work function was assumed
to be that of graphite (~5 eV) and a field enhancement factor could be

calculated from the Fowler-Nordheim curve. The calculated values of ,6
were 39400 and 72970 cm'1 for nanotubes grown on Ni and Fe tips,

respectively. The reported values of the field enhancement factors were in
the range of 500 to 10000 cm.1 for an array of carbon nanotubes
[125,9,139,218] and 30000 to 240000 for single nanotube [137,213]. Figure 4-

26 shows that nanotubes on the tip were intact after the field emission

measurement.

4.4 Summary
Field emission mapping revealed non-uniform distribution of emission

sites and emission currents. Secondary nucleation on the diamond film surface

140

which resulted in an increase of density of grain boundaries played an important

role in improving the electron emission. High quality diamond grains in the vicinity

of high density of grain boundaries were crucial for high field emission current.
The clusters deposited during nanotube fabrication hindered field

emission. The electron emission was dependent on the orientation of
nanotube. The turn-on field to produce 10 uA/cm:2 from nanotube film was
obtained at 2.3 V/um. The field emission of nanotubes deposited on metal
tips was studied. l-V characteristics followed the Fowler-Nordheim

behavior, indicating that electron emission was due to the field emission

process.

141

—l-

CHAPTER 5

FIELD EMISSION ELECTRO—LUMINESCENCE
(FEEL) IN POLY-C

5.1 Introduction

Although electro-luminescence during field emission from carbon
nanotubes was studied by other researchers, we reported field emission
electro-luminescence (FEEL) on CVD diamond for the first time. I-V
characteristics and spectral data of FEEL were studied. The qualitative

models for FEEL and hysteresis behavior of emission current are proposed.

5.2 Field Emission Electra-luminescence Characterization

Setup

The collected luminescence spectra through the optical fiber (1000
pm thick fused silica, Ocean Optics, inc.) were analyzed by the
spectrometer (PC2000 PC plug-in spectrometer, Ocean Optics, lnc.). The
spectrometer was responsive from 350 to 1000 nm and couples via an SMA
905 connector to the optical fiber. The resolution was 5 nm full width at half
maximum (FWHM). The slit with 50 um wide and 1000 um tail was installed.

The schematic of the system is shown in Figure 5-1.

142

 

 

 

Optical fiber

 

Spectrometer

 

 

 

 
  
 

Copper supporting rod

 

Tungsten anode

Cathode

 

tueuJeruJ-z

insulator

 

XY-manipuiator

 

 

 

 

 

Figure 5-1: Schematic diagram of field emission electro-
iuminescence characterization setup.

143

The optical fiber was attached by the anode in the field emission
characterization system which is described in Figure 4-1. The jacket and
sheathing of the fiber inside the vacuum chamber were removed to
minimize outgasing from them, and to attach easily to the probe anode. The

fiber was positioned at 2 mm above the emitting surface.

5.3 Field Emission Eiectro-luminescence

Electro-iuminescence during field emission from poly-diamond and
carbon nanotubes was observed. The emission current characteristics and

spectral data from FEEL are discussed.

5.3.1 CVD Diamond

The poly-diamond films grown by CVD methods contained structural
defects and non-diamond phases, which gave rise to localized electronic
states within the band gap [30,45,200]. There was experimental evidence

that electron emission was related to defects in the films [29,39,198,199].

. Film fabrication

Diamond films were grown on p-type Si (100) and free-standing

diamond substrates by MPCVD. Trimethylboron (diluted in H2) was used as

a doping source for boron. Diamond films were deposited at 700 C with

1.5 °/o CH4 in H2.

144

 

 

1.E-04 1
1.E-05 _
1.E-06 ~

1.E-07 ~

Emission Current (A)

1.E-08 -

FEEL

N0 FEEL

 

 

1.E-09
20

r 1 l l

40 60 80 100
Field (V/um)

 

Figure 5-2:

l-V characteristics with and without FEEL for
undoped polycrystalline dlamond film.

145

 

 

 

1.E-05 -

1.E-06 ~

Emission Current (A)

1.E-10 -

1.E-11

1.E-07 -

1.E-08 —

1.E-09 J

 

34 V/um
24 V/um

 

10

j l 1

20 30 ml
Applied Field (V/um)

 

 

Figure 5-3: i-V characteristics with FEEL from B-doped

free-standing diamond film.

146

 

 

1 .E-05

l

l

1 .E-06

1 .E-07

l

1

1 .E-08

Emission Current (A)

1.E-09

1

 

 

1.E‘1 0 I I I I
0 20 40 60 80 100
Applied Field (V/um)

 

 

Figure 5—4: i-V characteristics with FEEL from undoped
poly-diamond.

147

 

 

No precise values of resistivity of B-doped films were available since no
electrical insulating layers were used between the films and p-type
substrates. The resistivity for B-doped poly-diamond was roughly in the
range of 0.05 - 0.5 £20m from the doping study in Section 3.3.3. The
resistivity for the doped films on the free-standing diamond wafer was
about 0.275 9cm. There was no intention of doping for undoped films.
However, all films were terminated with hydrogen plasma for 5 min after

growth.

. Field emission electro-luminescence

The field emission measurements were carried out at room
temperature in a dark chamber to isolate it from surrounding light sources.
Figure 5-2 shows two field emission curves measured at two different
points on a poly-diamond film. FEEL was observed only for sites which
showed a rapid increase of emission current. The emission current
gradually saturated at high fields. The combination of space charge
buildup and carrier saturation was taken into account for the current
saturation. it was proposed that the vacuum space charge surrounding an
emission site reduced the actual electric field at the emitter at high current
[210]. Saturation of the emitter current due to limited carrier concentration
could add to the space charge effect [219]. However, in this work, electrons
contributed to field emission as well as electro-luminescence. The intensity

of luminescence was almost a linear function of emission current, which

148

will be discussed later in this chapter. in other words, electrons taking part
in electro-luminescence remained constant if the emission current
saturated. The current at the low field regime of less than 40 V/um was
believed to be leakage currents. For sites that exhibited FEEL, an emission
current of mm was required both for increasing and decreasing emission
fields as seen in Figures 5-3 and 5-4, which were for B-doped large grain
free-standing diamond and undoped poly-diamond, respectively. Once
activated at the threshold, FEEL was sustained at electric fields much
lower than the threshold field. The FEEL from B-doped free-standing
diamond, initiated around 34 V/um, continued at decreasing fields and
stopped at 24 V/um. FEEL, once triggered, was very stable and
reproducible. The hysteresis behavior was repeatable. The field emission
current behavior with FEEL from undoped poly-diamond was similar to the
one from doped free-standing diamond except that luminescence was
observed at the higher field than B-doped free-standing diamond. FEEL
was observed at 76 V/um with increasing field, and was terminated at 44
V/um on decreasing field. Figure 5-5 shows luminescence spectra acquired
at the emission current of 17.2 [11A from B-doped free-standing diamond.
The peak position of the main luminescence center occurred at 482 nm and
a small peak appears at 638 nm. The main peak had a shoulder at 442 nm.
A peak at 482 nm was observed from the electro-iuminescence study of
diamond film [90]. The peaks at 442 and 638 nm could be associated with

growth induced dislocation and vacancy, respectively [86,87].

149

 

 

 

400 d

 

 

l 482 nm
442 nml
3 300 —
£8
’3‘ l 638 nm
C
Q
5 200 -
17.2 “A
3.1eV 2.07eV 1.55ev 1.24eV Energy
100 i i l 1e i
200 400 600 800 1 000 1 200

Wavelength (nm)

‘

 

 

Figure 5-5: Luminescence spectra from B-doped free-
standing diamond film.

150

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5g 8.0E-06-/
2
3 6.0E-06-/
é 4.0E-06-/
(D
E 2.0E-06-/
LU
0.0E+00-

 

Figure 5-6: Field emission mapping for B-doped poly-

diamond.

151

 

 

 

 

2500 1

 

 

 

 

 

 

 

 

2000 1
’5
5;; 1500 ~
.?:‘
(D
5
E 1000 1
500 ~
0 3.1eV 2.07eV 1.556V Energy
200 400 600 800 1 000
(a) Wavelength (nm)
2400 1 532 nm
3
E; 1800 1 503 nm
E
g 1200 —~ 627 nm
E 445 nm
_l 600 ~
0.1
O T T I I
O 5 10 15 20
(b) Emission Current (uA)

 

 

 

Figure 5-7: (a) Luminescence spectra with variation of
emission current and (b) luminescence
intensity as a function of emission current.

152

The field emission mapping of B-doped poly-diamond film is shown in

Figure 5-6. The film was grown at the temperature of 700 C with the mixture

of 4% of CH4 in H2 and trimethyiboron for 2 hours. The field emission

mapping revealed that there were a number of sites emitting currents
above 1 [1A. However, not every site exhibited FEEL. Some of the lower
current sites showed a higher intensity of luminescence than the higher
current sites. The intensity of luminescence at each emission site
increased with the emission current as seen in Figure 5-7. The peak
positions remained constant. The corresponding emission currents were in
the range of 2.5 to 14.7 uA. The peak at 532 hm could be related to nitrogen
[76]. Figure 5-7(b) shows that the luminescence intensity was nearly a

linear function of emission current at different wavelengths.

5.3.2 Carbon Nanotubes

Highly oriented carbon nanotubes were deposited uniformly on the

substrate. The diameter and density of the tubes were in the range of 20 —

100 nm and 108- 109 cm'z, respectively. The field emission mapping study

on carbon nanotube films discussed in the section 4.3.2.1 showed
relatively uniform emission current and high density of emission sites. The
luminescence was observed during the field emission using a pointed
tungsten anode at a distance of 50 um. Three luminescence spectra from

different emitting sites were shown in Figure 5-8.

153

 

Intensity (a.u.)

 

800 J

600 4

 

h

C

O
l

2.68 11A

200 — (ii) M1593 IIA
(iii) 7.66 11A

3.1eV 2.07eV 1.55eV 1.24eV

 

 

 

 

 

O l i l l ‘Jl
200 400 600 800 1000 1200
Wavelength (nm)
(b)

 

 

 

 

whorls

MIG-“J
J.

 

a 1 ' 1 1

 

I L. 1 20“
1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.“ 2

Erwiovl

Figure 5-8: (a) Luminescence spectra of different FEEL
sites from carbon nanotube film and (b) spectra
from MWNTS in literature [2.148].

154

 

The sharp and broad peaks were superimposed on the spectra. The sharp
peaks were indicative of discrete transitions between energy levels
whereas broad bands indicative variable transition energies [73]. Most of
the peaks were within visible range (430 — 690 nm) and their positions were
different from the values reported in the literature [155]. Interestingly, the
four peaks (460, 506, 549, 592 nm) in the spectra (i) in Figure 5-8 were
roughly equally spaced. The spectra (iii) exhibited a broad peak at 646 nm.
The second spectra consisted of two narrow peak at 448 and 490 nm

positioned on top of the spectra (iii).

5.4 Qualitative Model

The qualitative models for FEEL and hysteresis loop of the emission

current from poly-diamond films are described in detail.

5.4.1 Field Emission Electra-luminescence

A constant supply of electrons is needed to sustain electron
emission. It was speculated that the grain boundary might form a
conduction channel [220,221]. However, electron emission at low field was
also achieved on mono-crystalline diamond. it was observed that impurity
conduction existed in synthetic diamond [222]. However, the impurity level
in B-doped diamond was less than 0.4 eV above the valence band and

hence the conduction channel was several eVs below the emitting states.

155

 

      
 

 

EC

 

Energy Transition\\..3_£1
L-z-:-:-:~:-:-:-:-:-:-:-. \‘L

 

 

 

 

 

7 i
Defect Bands \:iji Surface
\ Potential
l:-:-:.:-:-:-:-:-32-32-3334? Barrier
\
Ev \
Surface
States
e: Electron

Figure 5-9: Quantitative model of field emission electro-
luminescence from poly-diamond film.

156

 

 

Another possible way of transporting electrons to the emitting surface was
through defect states. it was found that vacancy defects in diamond films
were substantial [223,224]. Dangling bonds are expected to exist in the
defects. if defect concentration is significant, the electron states in these
defects can form a band or bands in the band gap. The formation of these
defect bands may raise the Fermi level into the upper part of the band gap,
and thus reduce the energy barrier that the electrons must tunnel through.
if defect bands exist in the band gap, they transport electrons to the
surface states. if the surface states are closely spaced, electrons can be
hopping to the higher surface states closer to the conduction band and
contribute to the field emission current. A fraction of electrons at the
surface states drops to lower energy levels. The direct energy transitions
between surface states are suggested to lead to FEEL. Figure 5-9 illustrates

the schematic diagram of FEEL.

5.4.2 Hysteresis Loop

The field emission current with FEEL from poly-diamond film show
hysteresis behavior with respect to the increasing and decreasing fields.
Steady-state heat balance may account for hysteresis in the electro-

luminescence of diamond films.

The rate R+ of energy deposition and heating in a region of sample

subjected to an external field E is given by

157

R+ = 171(Tim)E (5.1)

Where I is the emission current and 77 describes the efficiency of current

conversion to heat. 7] is assumed to be temperature-independent in the
relevant temperature range and is non-Ohmic in origin. At the same time, it
is to be expected that 7] depends on defect density, since this alters

resistivity by changing the electron scattering length. it is also assumed
that current depends implicitly on a temperature Tin, in the field region
through a temperature-dependent resistivity.

The rate of cooling R_ is assumed to depend on the difference
between the temperature Tim of atoms or molecules in the field region of the
film and the temperature Text of the substrate. With the definition AT 5 Tim—

Text, we write

R = CAT (52)

where c is assumed to be a constant in the relevant temperature range. The
sample dependence implicit in cooling constant c can be parameterized by
assuming proportionality to thermal conductivity K, through a density- and

geometry-dependent factor g (c = gK).

Under steady-state conditions we can equate the heating and cooling

rates from Equations (5.1) and (5.2) by setting

R+ = R_ (5.3)

158

l (Tint) (uA)

 

_ Eq (5.7)

2 1
Text/

 

 

E = 20 V/um

l

I I

 

E= 0V/um

l

 

 

300

Figure 5-10: Dependence of current on temperature. The straight

lines are plots of AI- for different values of E.

159

 

 

l(T int) (uA)

NCO-P-

7-

6

U1

O_L

Edown = 25.5 V/um

 

 

 

 

 

 

‘1 \Cf '

— l Eup = 35 V/um
JM

1 0 20 30 40 50

Electric field, E (V/um)

 

Figure 5-11: Replot of Figure 5-10; Dependence of
current on electric field.

160

 

By substituting Equations (5.1) and (5.2) into Equation (5.3), it becomes

7710mm = cAT (5.4)
c AT
I (Tim) = —— (5.5)

By defining the ratio of heating and cooling constants to be 5 5 77/6, this

yields an equation relating current to the applied field and temperature.

AT
1(T- )-—=0 (5.6)

“It a

The current for a fixed field is determined at different equilibrium

temperatures of the sample. This establishes the functional dependence of
current on temperature, l(Tint). in a defective material, a temperature-

dependent current might be expected on the basis of a thermally-mediated
release of charge carriers. in order to illustrate the dependence of current

on temperature, a hyperbolic tangent function is used.
_ :1: _
I (Tim) — a Tanh((Tint b)/ C) + d (5,7)

a, b, c, and d are chosen to be 0.0000025, 360, 18.6, and 0.0000032,
respectively, to make a fit into the experimental data. Figure 5-10 displays
that solutions of Equation (5.6) can be obtained graphically as the
intersections of the curve for Equation (5.7) with the plot

_1_

IT. =
(mt) 5E

(Tilnt - T ) (5.8)

ext

161

Tax, and l; are assumed to be room temperature (300 K) and 0.1, respectively.
The straight lines in Figure 5-10 are plotted by varying E values in Equation
(5.8). The intersecting point is initially single valued as the straight line of
Equation (5.8) crosses only once the curve for current (Equation 5.7). As E
increases, there are two intersecting points at E = 25.5 V/um. The current
does not jump to the higher point since the local solution is available. Once
the field exceeds the value E = 35 V/um, the local solution is no longer
available. The current is forced to jump to the non-local solution which has
a much higher current level indicated by dots in Figure 5-10. There is a
single solution for Equation 5.6 when the field is greater than 35 V/um.
When the field is decreasing, similar arguments can be applied. The current
has a single value to begin with. The second solution is possible at E = 35
V/um, but the current stays at the local solution. When the field crosses the
value at E = 25.5 V/um, the current drops to lower value. Presuming that the
optical emission rates are proportional to the current, the luminescence
intensity jumps to a higher value at the same time. According to this
analysis, the switching fields are Eup = 35 V/um and Edam, = 25.5 V/um.
Figure 5-10 is replotted in Figure 5-11 in terms of the current values with
respect to the increasing and decreasing electric fields. The current stays
low level and jumps to high level at E = 35 V/um when the field is increasing.
At decreasing fields, the current stays high level until E = 25.5 V/um. The
current vs. electric field plot generates a hysteresis behavior. The FEEL

turn-on and terminating fields from the theoretical values are in good

162

agreement with the experimental data of 34 and 24 V/um for B-doped

diamond film, as shown in Figure 5-3.

5.4 Summary

FEEL was observed from B-doped/undoped microcrystailine and
large-grain freestanding poly-diamond and carbon nanotube films. The
FEEL intensity increased with the emission current. However, there was no
change in the peak position with the current. The analysis of luminescence
spectra revealed that the luminescence centers were related to the defects.
The quantitative models for FEEL and hysteresis behavior of emission

current from poly-diamond were discussed.

163

CHAPTER 6

CONCLUSIONS AND FUTURE RESEARCH

6.1 Summary and Conclusions

0 Direct patterning of diamond

A computer controlled patterning system was constructed. A 330 um
line and various patterns on 4 inch substrate were generated successfully
by direct writing method. Diamond uniform seeding over a 2 inch substrate
by spray nozzle was achieved. Diamond seeding patterns were produced

successfully by a modified printer.

. Fabrication of electron emitters

The resistivity in diamond films was achieved in the range of 0.001 —
450 52cm using TMB as boron doping source. Procedures was developed
for oriented nanotube growth and post-cleaning of nanotubes. Nanotubes

were successfully grown on a pointed metal tip.

. Spatial mapping of electron emission
Field emission mapping revealed non-uniform distribution of

emission sites and emission currents. High quality diamond grains in the

164

vicinity of high density of grain boundaries was crucial for high field
emission current. The electron emission was dependent on the orientation
of nanotube. Nanotubes on a tip was demonstrated as good electron

source.

. Field emission electro-iuminescence

FEEL was observed from poly-diamond for the first time. The FEEL
intensity increased with the emission current. The analysis of
luminescence spectra revealed that the luminescence centers were related
to the defects. The quantitative models for FEEL and hysteresis behavior of

emission current were proposed.

6.2 Future Research

Although in the present study, field emission electro-iuminescence
was observed and characterized for the first time, the following areas need
to be addressed.

(i) The fabrication of practical cathodes remains unresolved. As
field emission mapping study revealed, efforts should be made
to improve the uniformity and site density of electron emission

(ii) Exact mechanisms of the electron transport through the film,
as well as of electro-luminescence during field emission

remain subjects of theoretical modeling and discussions.

165

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[81

[9]

[10]

Bibliography

K. R. Shoulders, Adv. Computers 2, 135, 1961.

C. A. Spindt, i. Brodie, L. Humphrey, and E. R. Westerberg, “Physical
properties of thin film field emission cathodes with molybdenum cones”, J.
Appl. Phys., 47, 5248, 1976.

T. Utsumi, “Vacuum microelectronics: what’s new and exciting”, IEEE
Trans. Electron Dev., 38, 2276, 1991.

H. H. Busta, “Review vacuum microelectronics - 1992”, J. Micromech.
Microeng., 2, 43, 1992.

l. Brodie and P. R. Schwoebel, “Vacuum microelectronic devices”, Proc.
lEEE, 82, 1006. 1994.

D. 8. Hong and D. M. Aslam, “Poly-diamond gated field-emitter display
cells”, IEEE Trans. Electron Dev., 46, 787, 1999.

K. Okano, K. Hoshina, M. lida, 8. Koizumi, and T. lnuzuka, “Fabrication of
a diamond field emitter array”, Appl. Phys. Lett., 64, 2742, 1994.

J. M. Bonard, J. P. Saivetat, T. Stockli, L. Forro, and A. Chatelain, “Field
emission from carbon nanotubes: perspectives for applications and clues
to the emission mechanism”, Appl. Phys. A 69, 245, 1999.

X. Xu and G. R. Brandes, “A method for fabricating large-area, patterned,
carbon nanotube field emitters”, Appl. Phys. Lett., 74, 2549, 1999.

U. Hoffmann, A. Weber, T. Lohken, C.-P. Kiages, C. Spaeth, F. Richter,
“Electron field emission of amorphous carbon films”, Diamond Relat.
Mater., 7, 682, 1998.

166

[11]

[12]

[131

[14]

[15]

[15]

I19]

[20]

Y. Sohda, D. M. Tanenbaum, S. W. Turner, and H. G. Craighead,
“Fabrication of arrayed glassy carbon field emitters”, J. Vac. Sci. Technol.
B15,343, 1997.

M. W. Geis, J. C. Twichell, and T. M. Lyszczarz, “Diamond emitters
fabrication and theory”, J. Vac. Sci. Technol. B 14, 2060, 1996.

L. A. Chernozatonskii, Y. V. Gulyaev, Z. Y. Kosakovskaya, N. i. Sinitsyn,
G. V. Torgashov, Y. F. Zakharchenko, E. A. Fedorov, and V. P. Valchuk,
“Electron field-emission from nanofilament carbon-films”, Chem. Phys.
Lett., 233, 63, 1995.

Yu. V. Gulyaev, L. A. Chernozatonskii, Z. Ja. Kosakovskaja, N. l. Sinitsyn,
G. V. Torgashov, and Yu. F. Zakharchenko, “Field emitter arrays on
nanotube carbon structure films”, J. Vac. Sci. Technol. B, 13, 435, 1995.

F. J. Himpsel, J. A. Knapp. J. A. Van Vechten, and D. E. Eastman,
“Quantum photoyield of diamond (111)-a stable negative-affinity emitter",
Phys. Rev. B 20,624,1979.

J. B. Cui, R. Graupner, J. Ristein, and L. Ley, “Electron affinity and band
bending of single crystal diamond (111) surface”, Diamond Relat. Mater.,
8, 748, 1999.

8. lijima and T. lchihashi, “Single-shell carbon nanotubes of 1-nm
diameter”, Nature, 363, 603, 1993.

T. W. Ebbesen and P. M. Ajayan, “Large-scale synthesis of carbon
nanotubes”, Nature, 358, 220, 1992.

C. Joumet and P. Bemier, “Production of carbon nanotubes”, Appl. Phys.
A, 67, 1, 1998.

L. Nilsson, O. Groning, C. Emmenegger, O. Kuttei, E. Schaller, L.
Schlapbach, H. Kind, J.-M. Bonard, and K. Kern, “Scanning field emission
from patterned carbon nanotube films”, Appl. Phys. Lett., 76, 2071, 2000.

167

[21]

[22]

[23]

[24]

[25]

[26]

I 271

[231

[291

[30]

[31]

A. T. Collins, “Diamond, SiC, and Relatred Wide Bandgap
Semiconductors”, J. T. Glass, R. Messier, N. Fujimori Eds., Pittsburg, PA;
Material’s Research Society, 3, 1990.

G. G. P. van Gorkan and A. M. E. Hoeberechts, “Performance of silicon
cold cathodes”, J. Vac. Sci. Technol. B 4, 108, 1986.

P. K. Bachmann and R. Messier, “Emerging technology of diamond thin
films”, C&EN Special Report, 1989.

P. K. Baumann and R. J. Nemanich, “Electron affinity and Schottky barrier
height of metal-diamond (100), (111), and (110) interfaces”, J. Appl. Phys.,
83, 2072, 1998.

2. H Haung, P. H. Cuttler, N. M. Kiskovsky, and T. E. Sullivan,
“Calculation of electron field emission from diamond surfaces”, J. Vac. Sci.
Technol. B 13,526, 1995.

E. l. Givargizov, V. V. Zhirnov, A. V. Kuznetsov, and P. S. Piekhanov,
“Cold emission from the single-crystalline microparticle of diamond on a 8i
tip”, J. Vac. Sci. Technol. B 14,2030, 1996.

P. Lerner, P. Cutler, and N. M. Miskovsky, “Theoretical analysis of field

emission from a metal diamond cold cathode emitter”, J. Vac. Sci. Technol.

B 15, 337, 1997.

Y. Gotoh, T. Kondo, M. Nagao, H. Tsuji, J. lshikawa, K. Hayashi, and K.
Kobashi, “Estimation of emission field and emission site of boron-doped
diamond thin-film field emitters”. J. Vac. Sci. Technol. B 18, 1018, 2000.

M. W. Geis, N. N. Efremow, J. D. Woodhouse, M. D. Aleese, M.
Marchywka, D. G. Socker, and J. F. Hochedez, “Diamond cold cathode”,
IEEE Elec. Dev. Lett., 12, 456, 1991.

M. w. Geis, J. c. Twichell, c. o. Bozler, o. o. Rathman, N. N. Efremow, K.
W. Krohn, M. A. l-lollis, R. Uttaro, and T. M. Lyszczarz, Proc. 6th int.
Vacuum Microelectronics Conf., 160, 1993.

C. Xie, C. N. Potter, R. L. Fink, C. Hilbert, A. Krishnan, D. Eichman, N.

Kumar, H. K. Schimidt, M. H. Clark, A. Ross, B. Lin, L. Fredin, B. Baker, D.

Patterson, and W. Brookover, “Use of diamond thin films for low cost field
emission displays”, Proc. 7th Int. Vacuum Microelectronics Conf., 229,
1994.

168

7

[32]

[33]

[34]

[35]

[36]

[371

[331

1391

[40]

[41]

[42]

K. Wu, E. G. Wang, J. Chen, and N. 8. Xu, “Nitrogen-incorporated
distorted nanocrystalline diamond films: Structure and field emission
properties”, J. Vac. Sci. Technol. B 17, 1059, 1999.

M. V. Ugarov, V. P. Ageev, A. V. Karabutov, E. N. Loubnin, S. M. Pimenov,
V. i. Konov, and A. Bensaoula, “Laser-induced modification of electron
field emission from nanocrystalline diamond films”, J. Appl. Phys., 85,
8436, 1999.

S. Jou, H. J. Doerr, and R. D. Bunshah, “Electron emission
characterization of diamond thin films grown from a solid carbon source”,
Thin Solid Films, 280, 256, 1996.

V. V. Zhirnov, O. M. Kuttei, O. Groning, A. N. Alimova, P. Y. Detkov, P. l.
Belobrov, E. Maiilard-Schaller, and L. Schlapbach, “Characterization of
field emission cathodes with different forms of diamond coatings”, J. Vac.
Sci. Technol. B 17, 666, 1999.

A. N. Obraztsov, l. Yu. Pavlovsky, A. P. Volkov, E. V. Rakova, and 8.. P.
Nagovitsyn, “Electron field emission from chemical vapor deposited
diamond films”, J. Electrochem. Soc., 145, 2572, 1998.

B. Ju; Y. Lee, and M. Oh, “Fabrication and field emission properties of
poly-diamond films”, Microelectronics J., 29, 855, 1998.

8. Kwon, Y. Shin, D. M. Aslam, and J. Lee, “Field emission pr0perties of
the polycrystalline diamond film prepared by microwave-assisted plasma
chemical vapor deposition”, J. Vac. Sci. Technol. B 16, 712, 1998.

W. Zhu, G. P. Kochanski, S. Jin, L. Seibles, D. C. Jacobson, M. Mc
Cormack, and A. E. White, “Electron field emission from ion-implanted
diamond”, Appl. Phys. Lett., 67, 1157, 1995.

N. A. Fox, 8. Mary, T. J. Davis, W. N. Wang, P. W. May, A. Bewick, J. W.
Steeds, and J. E. Butler, “Field-emission studies of boron-doped CVD
diamond films following surface treatments”, Diamond Relat. Mater., 6,
1135, 1997.

W. Zhu, G. P. Kochanski, 8. Jin, and L. Seibles, “Electron field emission

from chemical vapor deposited diamond”, J. Vac. Sci. Technol. B 14, 2011,

1 996.

Y. Chen, C. Hu, and l. Lin, “Field emission characteristics of boron-doped
diamond films prepared by MPE-CVD”, Appl. Surf. Sci., 142, 516, 1999.

169

1

[43]

[44]

[45]

[46]

[47]

[48]

[491

[50]

[511

[521

[53]

[541

K. Pemg, K. Liu, and I. Lin, “Modification on the band structure and the
related emission characteristics of defective diamond films doped with
boron”, Appl. Surf. Sci., 142,494, 1999.

C. Nutzenadel, O. M. Kuttei, O. Groning, and L. Schlapbach, “Electron
field emission from diamond tips prepared by ion sputtering”, Appl. Phys.
Lett., 69, 2662, 1996.

W. Zhu, G. P. Kochanski, S. Jin, and L. Seibles, “Defect-enhanced
electron field emission from chemical vapor deposited diamond”, J. Appl.
Phys., 78, 2707, 1995.

K. Okano, T. Yamada, A. Sawabe, S. Koizumi, R. Matsuda, C. Bandis, W.
Chang, and B. B. Pate, “Characterization of electron emission from N-
doped diamond using simultaneous field emission and photoemission
technique”, Appl. Surf. Sci., 146,274, 1999.

M. W. Geis, J. C. Twichell, N. N. Efremow, K. Krohn, and T. M. Lyszczarz,
“Comparison of electric field emission from nitrogen-doped, type lb
diamond, and boron-doped dia'mondl’, Appl. Phys. Lett., 68, 2294, 1996.

K. Okano, S. Koizumi, S. Ravi, P. Silva, and G. A. J. Amaratunga, “Low-
threshold cold cathodes made of nitrogen-doped chemical-vapour-
deposited diamond “, Nature, 389, 140, 1996.

M. W. Geis, N. N. Efremow, K. E.. Krohn, J. C. Twichell, T. M. Lyszczarz,
R. Kalish, J. A. Greer, and MD. Tabat, “A new surface electron-emission
mechanism in diamond cathodes”, Nature, 393, 431, 1998.

C. Kimura, K. Kuriyama, S. Koizumi, M. Kamo, and T. Sugino, “Field
emission characteristics of phosphorus-doped hommoepitaxial diamond
films”, Appl. Surf. Sci., 146, 295, 1999.

K. Park, S. Lee, K. Song, J. Park, K. Park, 8. Han, 8. Na, N. Lee, and K.
Koh, “Field emission characteristics of defective diamond films”, J. Vac.
Sci. Technol. B 16, 724, 1998.

W. Mueller, H. S. Dewan, H. Chen, G. T. Mearini, and l. L. Krainsky, “Field
emission from gated diamond arrays”, Appl. Surf. Sci., 146, 328, 1999.

S. Albin, W. Fu, A. Carghese, A. C. Lavarias and G. R. Myneni, “Diamond
coated silicon field emitter array”, J. Vac. Sci. Technol. A 17, 2104, 1999.

V. V. Zhirnov, E. l. Givargizov, A. V. Kandidov, B. V. Seieznev, and A. N.

Alimova, “Emission characterization of diamond-coated Si field emission
arrays”. J. Vac. Sci. Technol. B 15, 446, 1997.

170

.1

[551

[56]

[571

[58]

[59]

[60]

[61]

[62]

[63]

154]

[55]

S. Yang, and M. Yokoyama, “Electron emission behaviors of
polycrystailine-diamond-coated silicon emitters”, Jpn. J. Appl. Phys., 38,
209.1999.

J. Liu, V. V. Zhirnov, A. F. Myers, G. J. Wojak, W. B. Choi, J. J.Hren, S. D.
Wolter, M. T. McClure, B. R. Stoner, and J. T. Glass, “Field emission
characterization of diamond coated silicon field emitter”, J. Vac. Sci.
Technol. B 13,422, 1995.

J. Chen, Z. Deng, N. S. Xu, K. H. Wu, and E. G. Wang, “Observation of a
non Fowler-Nordheim field-induced electron emission phenomenon from
chemical vapor deposited diamond films”, Appl. Phys. Lett., 75, 1323,
1999.

M. Liao, Z. Zhang, W. Wang, and K. Liao, “Field-emission current from
diamond film deposited on molybdenum”, J. Appl. Phys., 84, 1081, 1998.

A. Wisitsora-at, W. P. Kang, J. L. Davidson, W. Li, J. F. Xu, and D. V.
Kems, “Efficient electron emitter utilizing boron-doped diamond tips with
sp2 content", Appl. Surf. Sci., 146, 280, 1999.

Z. Tolt, R. L. Fink, and Z. Yaniv, “Electron emission from patterned
diamond flat cathodes”, J. Vac. Sci. Technol. B 16, 1197, 1998.

M. W. Geis, “Application of diamond films and related materials”, Elsevier,
Amsterdam, 309, 1991.

C. Wang, A. Garcia, I. C. lngram, M. Lake, and M. E. Kordesch,” Cold
field-emission from cvd diamond films observed in emission electron-
microscopy”. Electron Lett., 27, 1459, 1991.

A. A. Blyablin, A. V. Kandidov, A. A. Pilevskii, A. T. Rakhimov, V. A.
Samorodov, B. V. Seieznev, N. V. Suetin, and M. A. Timofeev,
“Examination of electron field emission efficiency and homogeneity from
CVD carbon-type films”, Proc. 11th int. Vacuum Microelectronics Conf.,
234, 1998.

W. Zhu, G. P. Kochanski, and S. Jin, “Low-field electron emission from
undoped nanostructured diamond”, Science, 282, 1471, 1998.

Y. Show, F. Matsuoka, M. Hayashi, H. lto, M. lwase, and T. lzumi,

“influence of defects on electron emission from diamond films”, J. Appl.
Phys., 84,6351, 1998.

171

7

[66]

[671

[53]

[691

I70]

[71]

[721

[73]

[74]

[75]

D. Hong and D. M. Aalam, “Technology and characterization of diamond
field emitter structures”, iEEE Trans. Electron Dev., 45, 977, 1998.

F. Lacher, C. Wild, D. Behr, and P. Koidi, “Electron field emission from thin
fine-grained CVD diamond films”, Diamond Relat. Mater. 6, 1111, 1997.

J. Luo, K. Liu, J. Lee, I. Lin and H. Chang, “The influence of film-to-
substarate characteristics on the electron field emission behavior of the
diamond films”, Diamond Relat. Mater., 7, 704, 1998.

B. L. Weiss, A. Badzian L. Pilione, T. Badzian, and W. Drawl, “Fabrication
of thin-film cold cathodes by a modified chemical vapor deposited
diamond process”, J. Vac. Sci. Technol. B 16, 681, 1998.

l. T. Han, N. Lee, S. W. Lee, S. H. Kim and D. Jeon, “Field emission of
nitrogen-doped diamond films”, J. Vac. Sci. Technol. B 16, 2052, 1998.

M. Q. Ding D. M. Gruen, A. R. Krauss, O. Auciello, T. D. Corrigan, and R.
P. H Chang, “Studies of field emission from bias-grown diamond thin films”,
J. Vac. Sci. Technol. B 17, 705, 1999.

A. R. Lang, A. P. W. Makepeace, and J. E. Butler, “Synchrotron X-ray
microdiffraction measurements of lattice tilts within CVD diamond
crystallites terminated by cathodoluminescent biue-cross-quartered cube
facets”, Diamond Relat. Mater., 7, 1698, 1998.

G. Faggio, M. Marineili, G. Messina, E. Milani, A. Paoletti, S. Santangelo,
A. Tucciarone, and G. V. Rinati, “Comparative study of band-A
cathodoluminescence and Raman spectroscopy in CVD diamond films”,
Diamond Relat. Mater., 8, 640, 1999.

K. Hayashi, S. Yamanaka, H. Watanabe, T. Sekiguchi, H. Okushi, and K.
Kajimura, “Investigation of the effect of hydrogen on electrical and optical
properties in chemical vapor deposited on homoepitaxial diamond films”, J.
Appl. Phys., 81, 744, 1997.

H. Kawarada, Y. Yokota, Y. Mori, K. Nishimura, and A. Hiraki,
“Cathodoluminescence and electroluminescence of undoped and boron-
doped diamond formed by plasma chemical vapor-deposition”, J. Appl.
Phys., 67,983, 1990.

172

[761

[771

[78]

[79]

» [80]

[811

[32]

[83]

[841

[85]

L. H. Robins and D. R. Black, “Defect mapping of a synthetic diamond
single-crystal by cathodoluminescence spectroscopy”, J. Mater. Res., 9,
1298, 1994.

A. T. Collins and S. C. Lawson, “Cathodoluminescence studies of isotope
shifts associated with localized vibrational-modes in synthetic diamond”. J.
Phys. Condens. Mater., 1, 6929, 1989.

A. T. Collins and G. S. Woods, “isotope shifts of nitrogen-related localized
mode vibrations in diamond”. J. Phys. C 20, L797, 1987.

A. T. Collins, G. Davies, H. Kanda, and G. 8. Woods, “Spectroscopic
studies of c-13 synthetic diamond”. J. Phys. C 21, 1363, 1988.

A. T. Collins, M. Kamo, and Y. Sato, “A spectroscopic study of optical-
centers in diamond grown by microwave-assisted chemical vapor-
deposition”J. Mater. Res., 5, 2507, 1990.

T. Feng and B. D. Schwartz, “Characteristics and origin of the 1.681 ev
luminescence center in chemical-vapor-deposited diamond films”, J. Appl.
Phys., 73, 1415, 1993.

Y. D. Glinka, K. W. Lin, H. C. Chang, and 8. H. Lin, “Multiphoton-excited
luminescence from diamond nanoparticles”, J. Phys. Chem. 103, 4251,
1999.

L. Diederich, O. M. Kuttei, P. Aebi, and L. Schlapbach, “Electron affinity
and work function of differently oriented and doped diamond surfaces
determined by photoelectron spectroscopy”, Surf. Sci., 418, 219, 1998.

V. S. Tatarinov, Y. S. Mukhachev, and W. A. Parifianovich, “High-
temperature electroluminescence of diamond”, Sov. Phys. Semicond., 13,
956,1979.

H. Sternschulte, J. Horseling, T. Albrecht, K. Thonke, and R. Sauer,
“Characterization of doped and undoped CVD-diamond films by
cathodoluminescence”, Diamond Relat. Mater., 5, 585, 1996.

173

_|

[86]

[371

[83]

[89]

[90]

[91]

[92]

[93]

[94]

I95]

[96]

X. Yang, A. V. Barnes, M. M. Albert, R. G. Albridge, J. T. McKinley, N. H.
Tolk, and J. L. Davidson, “Cathodoluminescence and photoluminescence
from chemical-vapor-deposited diamond”, J. Appl. Phys., 77, 1758, 1995.

J. W. Steeds, 8. Charles, T. J. Davis, A. Gilmore, J. Hayes, D. Pickard,
and J. E. Butler, “Creation and mobility of self-interstitials in diamond by
use of a transmission electron microscope and their subsequent study by
photoluminescence microscopy”, Diamond Relat. Mater., 8, 94, 1999.

K. lakouvovskii, G. J. Adriaenssens, M. Nesladek, and L. M. Stals,
“Photoluminescence excitation and quenching spectra in CVD diamond
films”, Diamond Relat. Mater., 8, 717, 1999.

J. 18 Nijenhuis, S. M. Oisthoom, W. J. P. van Enckevort, and L. J. Giiing,
“Red luminescence in phosphorous-doped chemically vapor deposited
diamond”, J. Appl. Phys., 82, 419, 1997.

B. Zhang, S. Shen, J. Wang, J. He, H. R. Shanks, M. W. Leksono, and R.
Girvan, “Blue-green electroluminescence of free-standing diamond thin
films”, Chin. Phys. Lett., 11, 235, 1994.

C. Manfredotti, F. Wang, P. Poleselio, E. Vittone, F. Fizzotti, and A.
Scacco, “Blue-violet electroluminescence and photocurrent spectra from
polycrystalline chemical vapor deposited diamond film”, Appl. Phys. Lett.,
67, 3376, 1995.

R. Saito, G. Dresselhaus, and M. 8. Dresselhaus, “Physical Properties of
Carbon Nanotubes”, imperial College Press, London, 1998.

M. S. Dresselhaus, G. Dresselhaus, and R. Saito, “Physics of carbon
nanotubes”, Carbon, 33, 883, 1995.

R. Saito, M. Fujita, G. Dresselhaus, and M. S. Dresselhaus, “Electronic
structure of chiral graphene tubules”, Appl. Phys. Lett., 60, 2204, 1992.

N. Hamada, S.-l. Sawada, and A. Oshiyama, “New one-dimensional
conductors: graphitic microtubules”, Phys. Rev. Lett., 68, 1579, 1992.

L. Langer, V. Bayot, E. Grivei, J.-P. lssi, J. P. Heremans, C. H. Olk, L.
Stockman, C. Van Haesendonck, and Y. Abruynseraede, “Quantum

174

TI

[97]

[98]

[99]

[100]

[101]

[102]

[103]

[1 04]

[105]

transport in a multiwaiied carbon nanotube”, Phys. Rev. Lett., 76, 479,
1996.

H. Dai, E. W. Wong, and C. M. Lieber, “Probing electrical transport in
nanomaterials: conductivity of individual carbon nanotubes”, Science, 272,
523, 1996.

T. W. Ebbesen, H. J. Lezec, H. Hiura, J. W. Bennett, H. F. Ghaemi, and T.
Thio, “Electrical conductivity of individual carbon nanotubes”, Nature, 382,
54, 1996.

J. E. Fischer, H. Dai, A. Thess, R. Lee, N. M. Hanjani, D. L. Dehaas, and
R. E. Smalley, “Single-electron transport in ropes of carbon nanotubes”,
Science, 275, 1922, 1997.

H. Hiura, T. W. Ebbesen, K. Tanigaki, and H. Takahashi, “Raman studies
of carbon nanotubes”, Chem. Phys. Lett., 202, 509, 1993.

J. Kastner, T. Pichler, H. Kuzmany, S. Curran, W. Blau, D. N. Weldon, M.
Delamesiere, S. Draper, and H. Zandbegen, “Resonance Raman and
infrared spectroscopy of carbon nanotubes”, Chem. Phys. Lett., 221, 53,
1994.

W. S. Bacsa, D. Ugarte, A. Chatelain, and W. A. de Heer, “High-resolution
electron microscopy and inelastic light scattering of purified multishelled
carbon nanotubes”, Phys. Rev. B 50, 15473, 1994.

G. Ovemey, W. Zhong, and D. Tomanek, “Structural rigidity and low
frequency vibrational modes of long carbon tubules”, J. Phys. D 27, 93,
1993.

J. P. Lu, “Elastic properties of carbon nanotubes and nanoropes”, Phys.
Rev. Lett., 79, 1297, 1997.

E. Hernandez, C. Goeze, P. Bemier, and A. Rubio, “Elastic properties of C
and BnyNz composite nanotubes”, Phys. Rev. Lett., 80, 4502, 1998.

175

[1 06]

[1071

[108]

[109]

[110]

[111]

[112]

[113]

[114]

[115]

M. M. J. Treacy, T. W. Ebbesen, and J. M. Gibson, “Exceptionally high
Young’s modulus observed for individual carbon nanotubes”, Nature, 381,
678, 1996.

M. F. Yu, B. 8. Files, 8. Arepalli, and R. S. Ruoff, “Tensile loading of ropes
of single wall carbon nanotubes and their mechanical properties”, Phys.
Rev. Lett., 84, 5552,2000.

S. S. Xie, W. Z. Li, Z. W. Pan, B. H. Chang, and L. F. Sun, “Mechanical
and physical properties on carbon nanotube”, J. Phys. Chem. Solids, 61,
1153,2000.

T. Hertel, R. Martel, and P. Avouris, “Manipulation of individual carbon
nanotubes and their interaction with surfaces”, J. Phys. Chem. B 102, 910,
1998.

E. W. Wong, P. E. Sheehan, and C. M. Lieber, “Nanobeam mechanics:
elasticity, strength, and toughness of nanorods and nanotubes”, Science,
277, 1971, 1997.

M. R. Faivo, G. J. Clary, R. M. Taylor, V. Chi, F. P. Brooks, 8. Washbum,
and R. Superfine, “Bending and buckling of carbon nanotubes under large
strain”, Nature, 389, 582, 1997.

S. lijima, “Helical microtubes of graphitic carbon”, Nature, 354, 56, 1991.

T. W. Ebbesen, H. Hiura, J. Fujita, Y. Ochiai, S. Matsui, and K. Tanigaki,
“Patterns in the bulk growth of carbon nanotubes”, Chem. Phys. Lett., 209,
83, 1993.

G. H. Taylor, J. D. Fitzgerald, L. Pang, and M. A. Wilson, “Cathode
deposits in fullerene formation - microstructurai evidence for independent
pathways of pyrolytic carbon and nanobody formation”, J. Cryst. Growth,
135, 157, 1994.

D. T. Colbert, J. Zhang, S. M. McClure, P. Nikoiaev, Z. Chen, J. H. Hafner,
D. W. Owens, P. G. Kotuia, C. B. Carter, J. H. Weaver, A. G. Rinzler, and
R. E. Smalley, “Growth and sintering of fullerene nanotubes”, Science,
266, 1218.

176

[116]

[117]

[118]

[119]

[120]

[121]

D. S. Bethune, C. H. Kiang, M. S. de Vries, G. Gonnan, R. Savoy, J.
Cazquez, and R. Beyers, “Cobalt-catalysed growth of carbon nanotubes
with single-atomic-layer walls”, Nature, 363, 605, 1993.

W. K. Maser, J. M. Lambert, P. M. Ajayan, O. Stephan, and P. Bemier,
“Role of Y-Ni-B mixtures in the formation of carbon nanotubes and
encapsulation into carbon clusters”, Synthetic Metals, 77, 1, 1996.

L. A. Chernozatonskii, 2. Ja. Kosakovskaja, A. N. Kiselev, and N. A.
Kiselev, “Carbon films of oriented multilayered nanotubes deposited on
KBr and glass by electron beam evaporation”, Chem. Phys. Lett., 228, 94,
1994.

M. G8 and K. Sattier, “Vapor-condensation generation and STM analysis
of fullerene tubes”, Science, 260, 515, 1993.

T. Guo, P. Nikoiaev, A. G. Rinzler, D. Tomanek, D. T. Colbert, and R. E.
Smalley, “Self assembly of tubular fullerenes”, J. Phys. Chem., 99, 10694,
1995.

M. Endo, K. Takeuchi, S. lgarashi, K. Kobori, M. Shiraishi, and H. W.
Kroto, “The production and structure of pyrolytic carbon nanotubes”, J.
Phys. Chem. Solids, 54, 1841, 1993.

[122] W. K. Hsu, M. Terrones, J. P. Hare, H. Terrones, H. W. Kroto, and D. R. M.

[123]

[124]

Walton, “Electrolytic formation of carbon nanostructures”, Chem. Phys.
Lett., 262, 161, 1996.

P. Nikoiaev, M. J. Bronikowski, K. Bradley, F. Rohmund, D. T. Colbert, K.
A. Smith, and R. E. Smalley, “Gas-phase catalytic growth of single-walled
carbon nanotubes from carbon monoxide”, Chem. Phys. Lett., 313, 91,
1999.

J. Kong, A. M. Cassell, and H. Dai, “Chemical vapor deposition of
methane for single-walled carbon nanotubes”, Chem. Phys. Lett., 292, 567,
1998.

177

[125]

[126]

[127]

[128]

[129]

[130]

[131]

[132]

[133]

[134]

J. M. Bonard, J. P. Saivetat, T. Stockii, W. A. De Heer, L. Forro, and A.
Chatelain, “Field emission from single-wall carbon nanotube films”, Appl.
Phys. Lett., 73, 918, 1998.

C. Bower, 0. Zhou, W. Zhu, A. G. Ramirez, G. P. Kochanski, and S. Jin,
Mat. Res. Soc. Symp. Proc., 349, 319, 1994.

W. Zhu, C. Bower, O. Zhou, G. Kochanski, and S. Jin, “Large current
density from carbon nanotube field emitters”, Appl. Phys. Lett., 75, 873,
1999.

N. l. Sinitsyn, Y. V. Gulyaev, G. V. Torgashov, L. A. Chernozatonskii, Z.
Kosakovskaya, Y. F. Zakharchenko, N. A. Kiselev, A. L. Musatov, A. I.
Zhbanov, S. T. Mevlyut, and O. E. Glukhova, “Thin films consisting of
carbon nanotubes as a new material for emission electronics”, Appl. Surf.
Sci.,111,145,1997.

D. N. Davydov, P.A. Sattari, D. AlMawlawi, A. Osika, L. Haslett, and M.
Moskovits, “Field emitters based on porous aluminum oxide templates”, J.
Appl. Phys., 86, 3983, 1999.

W. A. De Heer, A. Chatelain, and D. Ugarte, “A carbon nanotube field-
emission electron source”, Science, 270, 1179, 1995.

8. Dimitrijevic, J. C. Withers, V. P. Mammana, O. R. Monteiro, J. W. Ager,
and l. G. Brown, “Electron emission from films of carbon nanotubes and
ta-C coated nanotubes”, Appl. Phys. Lett., 75,2680, 1999.

J. M. Bonard, N. Weiss, H. Kind, T. Stockli, L. Forro, K. Kern, and A.
Chatelain, “Tuning the field emission properties of patterned carbon
nanotube films”, Advanced Materials, 13, 184, 2001.

M. J. Fransen, Th. L. van Rooy, P. Kruit, “Field emission energy
distributions from individual multiwaiied carbon nanotubes”, Appl. Surf.
Sci., 146,312, 1999.

A. G. Rinzler, J. H. Hafner, P. Nikolaev, L. Lou, 8. G. Kim, D. Tomanek, P.
Nordlander, D. T. Colbert, and R. E. Smalley, “Unraveling nanotubes:
Field emission from an atomic wire”, Science, 269, 1550, 1995.

178

[135]

[136]

[1371

[1 38]

[139]

[140]

[141]

O. H. Wang, A. A. Setlur, J. M. Lauerhaas, J. Y. Dai, E. W. Seelig, and R.
P. H. Chang, “A nanotube-based field-emission flat panel display”, Appl.
Phys. Lett., 72, 2912, 1998.

W. A. De Heer, J. M. Bonard, T. Stockii, A. Chatelain, L. Forro, and D.
Ugarte, “Carbon nanotubes films: Electronic properties and their
application as field emitters”, Zeitschrift fur Physik D-Atoms Molecules and
Clusters, 40,418, 1997.

J. M. Bonard, F. Maier, T. Stockii, A. Chatelain, W. A. De Heer, J. P.
Saivetat, and L. Forro, “Field emission properties of multiwaiied carbon
nanotubes”, Uitramicroscopy, 73,7, 1998.

P. G. Collins and A. Zettl, “A simple and robust electron beam source from
carbon nanotubes”, Appl. Phys. Lett., 69, 1969, 1996.

O. H. Wang, T. D. Corrigan, J. Y. Dai, R. P. H. Chang, and A. R. Krauss,
“Field emission from nanotube bundle emitters at low fields”, Appl. Phys.
Lett., 70, 3308, 1997.

Y. Saito and S. Uemura, “Field emission from carbon nanotubes and its
application to electron sources”, Carbon, 38, 169, 2000.

E. D. Obraztsova, J. M. Bonard, V. L. Kuznetsov, V. l. Zaikovskii, S. M.
Pimenov, A. 8. Pozarov, S. V. Terekhov, V. l. Konov, A. N. Obraztsov,
and A. P. Volkov, “Structural measurements for single-wall carbon
nanotubes by Raman scattering technique”, Nanostructured Materials, 12,
567, 1999.

[142] O. M. Kuttei, O. Groning, C. Emmenegger, and L. Schlapbach, “Electron

[143]

field emission from phase pure nanotube films grown in a
methane/hydrogen plasma”, Appl. Phys. Lett., 73,2113, 1998.

8. Fan, M. G. Chapline, N. R. Franklin, T. W. Tombler, A. M. Cassell, and
H. Dai, “Self-oriented regular arrays of carbon nanotubes and their field
emission properties”, Science, 283, 512, 1999.

[144] A. N. Obraztsov, A. P. Volkov, I. Y. Pavlovskii, A. L. Chuvilin, N. A. Rudina,

and V. L. Kuznetsov, “Role of the curvature of atomic layers in electron
field emission from graphitic nanostructured carbon”, JETP Lett. 69, 411,
1999.

179

[145]

[146]

[147i

[148]

[149]

[150]

[151]

[152]

D. Xu, G. Guo, L. Gui, Y. Tang, 2. Shi, Z. Jin, Z. Gu, W. Liu, X. Li, and G.
Zhang, “Controlling growth and field emission property of aligned carbon
nanotubes on porous silicon substrates”, Appl. Phys. Lett., 75,481, 1999.

A. N. Obraztsov, l. Pavlovsky, A. P. Volkov, E. D. Obraztsova, A. L.
Chuvilin, and V. L. Kuznetsov, “Aligned carbon nanotube films for cold
cathode applications”, J. Vac. Sci. Technol. B, 18, 1059, 2000.

H. Murakami, M. Hirakawa, C. Tanaka, and H. Yamakawa, “Field emission
from well-aligned, patterned, carbon nanotube emitters”, Appl. Phys. Lett.,
76, 1776,2000.

Y. Chen, D. T. Shaw, and L. Guo, “Field emission of different oriented
carbon nanotubes”, Appl. Phys. Lett., 76, 2469, 2000.

W. Hong, H. Shih, S. Tsai, and C. Shu, “Field-emission properties of
aligned carbon nanotubes”, Jpn. J. Appl. Phys. 39, L925, 2000.

J. Han, W. Yang, J. Yoo, and C. Park, “Growth and emission
characteristics of vertically well-aligned carbon nanotubes grown on glass
substrate by hot filament plasma-enhanced chemical vapor deposition”, J.
Appl. Phys., 88, 7363,2000.

F. G. Tamtair, L. C. Chen, S. L. Wei, W. K. Hong, K. H. Chen, and H. C.
Cheng, “High current density field emission from arrays of carbon
nanotubes and diamond-clad Si tips”, J. Vac. Sci. Technol. 8, 18, 1207,
2000.

A. M. Rao, D. Jacques, R. C. Haddon, W. Zhu, C. Bower, and S. Jin, “In
situ-grown carbon nanotube array with excellent field emission
characteristics”, Appl. Phys. Lett., 76, 3813,2000.

[153] Y. Chen, S. Patel, Y. Ye, D. T. Shaw, and L. Guo, “Field emission from

[154]

aligned high-density graphitic nanofibers”, App. Phys. Lett., 73, 2119,
1998.

X. Ma, E. Wang, Z. Wuzong, D. A. Jefferson, C. Jun, D. Shaozhi, X.

Ningsheng, and Y. Jun, “Polymerized carbon nanobells and their field-
emission properties”, Appl. Phys. Lett., 75, 3105, 1999.

180

[155] J. M. Bonard, T. Stockii, F. Maier, W. A. de Heer, and A. Chatelain, “Field-

[156]

[157]

emission-induced luminescence from carbon nanotubes”, Phys. Rev. Lett.,
81,1441,1998.

R. Erz, W. Dotter, K. Jung, and H. Ehrhardt, “Preparation of smooth and
nanocrystalline of diamond films”, Diamond Relat. Mater., 2, 449, 1993.

Y. Hayashi, W. Drawl, R. W. Collins, and R. Messier, “in-process
eilipsometric monitoring of diamond film growth by microwave plasma
enhanced chemical vapor deposition”, Appl. Phys. Lett., 60, 2868, 1992.

[158] J. S. Ma, H. Kawarada, T. Yonehara, J. l. Suzuki, J. Wei, Y. Yokota, and A.

[159]

[160]

[161]

[162]

[163]

[1641

[165]

[166]

Hiraki, “Selective nucleation and growth of diamond particles by plasma-
assisted chemical vapor deposition”, Appl. Phys. Lett., 55, 1071, 1989.

M. P. Everson and M. A. Tamor, “Studies of nucleation and growth
morphology of boron-doped diamond microcrystals by scanning tunneling
microscopy”, J. Vac. Sci. Technol. B 9, 1570, 1991.

B. W. Sheldon, R. Csenesits, J. Rankin, and R. E. Boekenhauer, “Bias-
enhanced nucleation of diamond during microwave-assisted chemical
vapor deposition”, J. Appl. Phys., 75, 5001, 1994.

B. R. Stoner, G. H. Ma, S. D. Woiter, and J. T. Glass, “Characterization of
bias-enhanced nucleation of diamond on silicon by in vacuo surface
ananlysis and transmission electron microscopy”, Phys. Rev. B 45, 11067,
1992.

D. Lee and R. K. Singh, “Synthesis of (111) oriented diamond thin films by
electrophoretic deposition process”, Appl. Phys. Lett., 70, 1542, 1997.

A. Masood, M. Aslam, M. A. Tamor, and T. J. Potter, “Techniques for
patterning CVD diamond films on non-diamond substrates”, J.
Electrochem. Soc., 138, L67, 1991.

K. Hirabayshi, Y. Taniguchi, O. Takamatsu, T. lkeda, K. lkoma, and N.
lwasaki-Kurihara, “Selective deposition of diamond crystals by chemical
vapor deposition using a tungsten-filament method”, Appl. Phys. Lett., 53,
1815, 1988.

M. W. Leksono and H. R. Shanks, “Patterning of microwave plasma
deposited diamond films”, Mater. Res. Soc. Symp. Proc., 189, 87, 1991.

T. Roppel, R. Ramesham, C. Ellis, and S. Y. Kee, “Thin film diamond
microstructures”, Thin Solid Films, 212, 56, 1992.

181

[167]

[168]

[169]

[1 70]

[171]

[172]

[173]

H. Shiomi, “Reactive ion Etching of Diamond in 02 and CF4 Plasma, and
Fabrication of Porous Diamond for Field Emitter Cathodes”, Jpn. J. Appl.
Phys. 1 36, 7745,1997.

N. N. Efremow, M. W. Geis, D. C. Flanders, G. A. Lincoln, and N. P.
Economou, “Ion-beam-assisted etching of diamond”, J. Vac. Sci. Technol.
B 3, 416, 1985.

W. J. Zhang, C. Sun, I. Beiio, C. S. Lee, and S. T. Lee, “Bias-assisted
etching of polycrystalline diamond films in hydrogen, oxygen, and argon
microwave plasmas”, J. Vac. Sci. Technol. A 17, 763, 1999.

B. R. Stoner, G. J. Tessmer, and D. L. Dreifus, “Bias assisted etching of
diamond in a conventional chemical vapor deposition reactor”, Appl. Phys.
Lett., 62, 1803, 1993.

S. A. Grot, R. A. Ditizio, G. Sh. Gildenblat, A. R. Badzian, and S. J.
Fonash, “Oxygen based electron cyclotron resonance etching of
semiconducting homoepitaxial diamond films”, Appl. Phys. Lett., 61, 2326,
1992,

M. Karisson, K. Hjort, and F. Nikolajeff, “Transfer of continuous-relief
diffractive structures into diamond by use of inductively coupled plasma
dry etching”, Optics Letters, 26, 1752, 2001.

L. Ackerrnann, and W. Kulisch, “investigation of diamond etching and
growth by in situ scanning tunneling microscopy", Diamond Relat. Mater.,
8, 1256, 1999.

[174] B. Y. Liaw, T. Stacy, G. Zhao, E. J. Charlson, E. M. Charlson, J. M. Meese,

[175]

[176]

[177]

and M. A. Prelas, “Plasma etched polycrystalline hot-filament chemical
vapor deposited diamond thin films and their electrical characteristics”,
Appl. Phys. Lett., 65, 2827, 1994.

M. Rothschild, C. Arnone, and D. J. Ehrlich, “Excimer-iaser etching of
diamond and hard carbon films by direct writing and optical projection”, J.
Vac. Sci. Technol. B 4, 310, 1986.

R. Ramesham, W. Welch, W. C. Neely, M. F. Rose, and R. F. Askew,
“Plasma etching and patterning of CVD diamond at <100 degrees C for
microelectronics applications”, Thin Solid Films, 304, 245, 1997.

M. E. Baginski, T. A. Baginski, and J. L. Davidson, “Characterization of the

ion-implantation and thermal annealing of boron in (100) diamond”, J.
Electrochem. Soc., 137, 2984, 1990.

182

[178]

[179]

[180]

[181]
[182]
[183]

[184]

W. Tsai, M. Deifino, D. Hodui, M. Riaziat, L. Y. Ching, G. Reynolds, and C.
B. Cooper, “Diamond MESFET using ultrashaliow RTP boron doping”,
IEEE Elect. Dev. Lett., 12, 157, 1991.

J. F. Prins, “Activation of boron-dopant atoms in ion-implanted
diamonds”Phys. Rev. B 38,5576, 1988.

Y. Show, T. Matsukawa, H. Ito, M. lwase, and T. lzumi, “Structural

changes in CVD diamond film by boron and nitrogen doping”, Diamond ‘

Relat. Mater. 9, 337, 2000.

X. Jiang, P. Willich, M. Paul, and C. -P. Kiages, “In situ boron doping of
chemical-vapor-deposited diamond films”, J. Mater. Res., 14, 3211, 1999.

K. Miyata, K. Kumagai, K. Nishimura, and K. Kobashi, “Morphology of
heavily b-doped diamond films”, J. Mater. Res., 8, 2845, 1993.

J. Cifre, J. Puigdollers, M. C. Polo, and J. Esteve, “Trimethylboron doping
of cvd diamond thin-films”, Diamond Relat. Mater. 3, 628, 1994.

A. Masood, M. Aslam, M. A. Tamor, and T. J. Potter, “Synthesis and
electrical characterization of boron-doped thin diamond films”, Appl. Phys.
Lett., 61, 1832, 1992. ‘

[185] D. N. Davydov, J. Li, K. B. Shelimov, T. L. Haslett, M. Moskovits, and B. W.

[1 86]

[1871

[1 88]

[189]

Staff, “Resistance and tunneling spectra of aligned multiwaiied carbon
nanotube arrays”, J. Appl. Phys., 88, 7205, 2000.

2. F. Ren, Z. P. Huang, J. W. Xu, J. H. Wang, P. Bush, M. P. Siegal, and
P. N. Provencio, “Synthesis of large arrays of well-aligned carbon
nanotubes on glass”, Science, 282, 1105, 1998.

H. M. Cheng, F. Li, X. Sun, 8. D. M. Brown, M. A. Pimenta, A. Mamcci, G.
Dresselhaus, M. S. Dresselhaus, “Bulk morphology and diameter
distribution of single-walled carbon nanotubes synthesized by catalytic
decomposition of hydrocarbons”, Chem. Phys. Lett., 289, 602, 1998.

G. S. Yang, M. Aslam, K. P. Kuo, D. K. Reinhard, and J. Asmussen,
“Effect of ultrahigh nucleation density on diamnd growth at different growth
rates and temperatures”, J. Vac. Sci. Technol. B 13, 1030, 1995.

A. Thess, R. Lee, P. Nikoaev, H. J. Dai, P. Petit, J. Robert, C. H. Xu, Y. H.
Lee, 8. G. Kim, A. G. Rinzler, D. T. Colbert, G. E. Scuseria, D. Tomanek,
J. E. Fischer, and R. E. Smalley, “Crystalline ropes of metallic carbon
nanotubes”, Science, 273, 483, 1996.

183

_l

[190]

[191]

[192]

[1 93]

[1 94]

[195]

[1 96]

[1971

[198]

[199]

[200]

J. Liu, A. G. Rinzler, H. Dai, J. H. Hafner, R. K. Bradley, P. J. Boul, A. Lu,
T. lverson, K. Shelimov, C. B. Huffman, F. Rodriguez-Macias, Y. Shon, T.
R. Lee, D. T. Colbert, and R. E. Smalley, “Fullerene pipes”, Science 280,
1253, 1998.

L. Forro, J. P. Saivetat, J. M. Bonard, R. Bacsa, N. H. Thomson, 8. Garaj,
L. Thien-Nga, R. Gaai, A. Kulik, B. Ruzicka, L. Degiorgi, A. Bachtold, C.
Schonenberger, S. Pekker, and K. Hemadi, Science and Application of
Nanotubes, edited by D. Tomanek and R. J. Enbody, Kluwer
Academic/Plenum Publishers, New York, 2000.

Y. Namba, E. Heidrarpour, and M. Nakayama, “Size effects appearing in
the Raman spectra of polycrystalline diamond”, J. Appl. Phys. 72, 1748,
1992.

R. Saito, T. Takeya, T. Kimura, G. Gresselhaus, and M. S. Dresselhaus,
“Finited-size effect on the Raman spectra of carbon nanotubes”, Phys.
Rev. B 59, 2388, 1999.

J. B. Bindell, “Scanning electron microscopy”, Encyclopedia of materials
characterization, Butterworth-Heinemann, Boston, 70, 1992.

L. Reimer, “Transmission electron microscopy. Physics of image formation
and microanaiysis”, Springer-Vedag, Berlin, 1984.

R. S. Howiand and M. D. Kirk, “Scanning tunneling microscopy and
scanning force microscopy”, Encyclopedia of materials characterization,
Butterworth-Heinemann, Boston, 85, 1992.

D. 8. Hong and M. Aslam, “Field-emission from p-type polycrystalline
diamond films”, J. Vac. Sci. Technol. B 13, 427, 1995.

D. 8. Hong, D. M. Aslam, T. Grimm, L. Garbini and S. Bandy, “Field
emission from carbon implanted polycrystalline diamond film”, Tech. Dig.
of lVMC ‘97, 117, 1997.

Y. Li, D. M. Aslam and S. J. Kwon, “Low voltage emission characteristics
of the undoped polycrystalline-diamond field emitter by MPCVD”, Tech.
Dig. of lVMC ‘97, 509, 1997.

W. P. Kang, A. Wisitsora-at, J. L. Davidson, D. V. Kerns, Q. Li, J. F. Xu, C.
K. Kim, “Effect of sp(2) content and tip treatment an the field emission of
micropattemed pyramidal diamond tips”, J. Vac. Sci. Technol. B 16, 684,
1998.

184

[201] J. Angus and A. T. Collins, “Diamond films - electronic era elusive”, Nature,

[202]

[203]

[204]

[205]

[206]

[207i

[208]

[209]

[210]

370, 601 , 1994.

0. Hong, “Fabrication and characterization of diamond field emitters for
field emission displays”, Ph. D. Dissertation, Michigan State University,
1997.

H. Dai, J. H. Hafner, A. G. Rinzler, D. T. Colbert, and R. E. Smalley,
“Nanotubes as nanoprobes in scanning probe microscopy”, Nature, 384,
147, 1996.

S. S. Wong, E. Joselevich, A. T. Wolley, C. L. Cheung, and C. M. Lieber,
“Covalently functionalized nanotubes as nanometre-sized probes in
chemistry and biology”, Nature, 394, 52, 1998.

R. Stevens, C. Nguyen, A. Cassell, L. Delzeit, M. Meyyappan, and J. Han,
“Improved fabrication approach for carbon nanotube probe devices”, Appl.
Phys. Lett., 77, 3453,2000.

G. Nagy, M. Levy, R.-Scarmozzino, R. M. Osgood, Jr., H. Dai, .R. E.
Smalley, C. A. Michaeis, G. W. Flynn, and G. F. McLane, “Carbon
nanotube tipped atomic force microscopy for measurement of < 100 nm
etch morphology on semiconductors”, Appl. Phys. Lett., 73, 529, 1998.

Y. Nakayama, H. Nishijima, S. Akita, K. I. Hohmura, S. H. Yoshimura, and
K. Takeyasu, “Microprocess for fabricating carbon-nanotube probes of a
scanning probe microscope”, J. Vac. Sci. Technol. B 18, 661, 2000.

J. H. Hafner, C. L. Cheung, and C. M. Lieber, “Growth of nanotubes for
probe microscopy tips”, Nature, 398, 761, 1999.

C. L. Cheung, J. J. Hafner, T. W. Odom, K. Kim, and C. M. Lieber,
“Growth and fabrication with single-walled carbon nanotube probe
microscopy tips”, Appl. Phys. Lett., 76, 3136,2000.

P. G. Collins and A. Zettl, “Unique characteristics of cold cathode carbon-
nanotube-matrix field emitters”, Phys. Rev. B 55, 9391, 1997.

[211] Y. Saito, K. Hamaguchi, R. Mizushima, S. Uemura, T. Nagasako, J. Yotani,

[212]

and T. Shimojo, “Field emission from carbon nanotubes and its application
to cathode ray tube lighting elements”, Appl. Surf. Sci., 146, 305, 1999.

W. B. Choi, Y. H. Lee, N. S. Lee. J. H. Kang, S. H. Park, H. Y. Kim, D. S.

Chung, S. M. Lee, S. Y. Chung, and J. M. Kim, “Carbon-nantubes for full-
color field-emission displays”, Jpn. J. Appl. Phys., 39, 2560, 2000.

185

[213]

[214]

[215]

[216]

[2171

[218]

[21 9]

[220]

[221]

[222]

[223]

[224]

D. Lovall, M. Buss, E. Graugnard, R. P. Andres, and R. Reifenberger,
“Electron emission and structural characterization of a rope of single-
walled carbon nanotubes”, Phys. Rev. B 61, 5683, 2000.

U. Kim, R. Pcionek, D. M. Aslam, and D. Tomanek, “Synthesis of high-
density carbon nanotube films by microwave plasma chemical vapor
deposition”, Diamond Relat. Mater., 10, 1947, 2001.

L. M. Baskin, O. I. Lvov, and G. N. Fursey, Phys. Status Solidi B 47, 49,
1971.

W. A. do Heer, J. .-M. Bonard, K. Fauth, A. Chatelain, L. Forro, and D.
Ugarte, “Electron field emitters based on carbon nanotube films”, Adv.
Mater. 9, 87, 1997.

D. T. Carroll, P. Redlich, P. M. Ajayan, J. -C. Charlier, X. Biasé, A. DeVita,
and R. Car, “Electronic structure and localized states at carbon nanotube
tips”, Phys. Rev. Lett., 78, 2811, 1997.

O. Groning, O. M. Kuttei, Ch. Emmenegger, P. Groning, and L.
Schlapbach, “Field emission properties of carbon nanotubes”, J. Vac. Sci.
Technol. B 18, 665, 2000.

A. Modinos, “Field, thermionic, and secondary electron emission
spectroscopy", Plenum, New York, 282, 1984.

Y. Muto, T. Sugino, and J. SHirafuji, “Electrical-conduction in undoped
diamond films prepared by chemical vapor-deposition”, Appl. Phys. Lett.,

59, 843, 1991.

A. V. Karabutov, V. D. Frolov. S. M. Pimenov, and V. l. Konov, “Grain
boundary field emission from CVD diamond films”, Diamond Relat. Mater.,
8,763, 1999.

A. W. 8. Williams, E. C. Lightowlers, and A. T. Collins, J. Phys. C 3, 1727,
1970.

M. Fanciulli and T. D. Moustakas, “Defects in diamond thin-films”, Phys.
Rev. B 48, 14982, 1993.

L. Aliers and A. Mainwood, “Surface vacancies in CVD diamond”,
Diamond Relat. Mater., 7, 261, 1998.

186