Fabrication of nanostructures using atomic force microscope assisted nanolithography

FABRICATION OF NANOSTRUCTURES USING
ATOMIC FORCE MICROSCOPE ASSISTED
NANOLITHOGRAPHY







SUBBIAH JEGADESAN
M. Sc.,(Madurai Kamaraj University, India)
M. Phil., (Cochin University of Science & Technology, India)






A THESIS SUBMITTED
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

DEPARTMENT OF CHEMISTRY

NATIONAL UNIVERSITY OF SINGAPORE
2007

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Dedicated to my parents











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It is my very great pleasure to express my heartfelt gratitude and sincere thanks to
Associate Professor Suresh Valiyaveettil for his guidance, support and encouragement
during the course of this work.
I am very thankful to Associate Prof. Regoberto C. Advincula, University of
Houstan, for his useful suggestion and valuable advice during this work.
My sincere thanks to all the current and former members of the group for their
cordiality and friendship. I thank Dr. C. Basheer, Dr. R. Lakshminarayanan, Dr. P. K.
Ajikumar, Ms. R. Renu, Ms. J. Akhila, Ms. S. Gayathri Dr. G. A. Rajkumar, Dr. M.
Vetrichelvan, Dr. Sivamurugan, Li Hairong, Michelle Low, Sheeja Bhahulayan,
Nurmawati, Ankur and Satyanand for all the good times in the lab. Also, i
am very much
grateful to Dr. Sindhu for her constant support and valuable suggestion during my work.
I owe my gratitude for the technical assistance provided by the staff of the XRD,

UV, IR, Mass spectroscopy, Elemental Analyses and Thermal Analysis Laboratories at
department of chemistry. Also, my sincere thanks to the staff of department general
office and chemical store.
I would like to thank Dr. Xie Xianning, Mr. Chung Hong jing, Miss. Li Hui, Mrs.
Ghee lee and all staff from NUS- Nanoscience Nanotechnology Initiative for their help
and assistance during my work.
I wish to express my deep gratitude to my family for their constant support and
motivation with full of kindness. I wholeheartedly thank my parents, sisters, brothers,
brother-in-law and parents-in-laws for their encouragement and support. My thanks are
also to all my friends and well-wishers.
I thank the
NUS - Nanoscience and Nanotechnology Initiative for granting the
research scholarship
for my research work.
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xxiii


Chapter 1 Introduction

1.1 Evolution of Nanotechnology 4

1.2 Development of Micro and Nanoscale Fabrication 5

1.2.1. Necessity of nanoscale fabrication 7
1.2.2 Nanofabrication 9
1.3 Lithographic Techniques 11
1.3.1 Optical lithography 11
1.3.2 Electron beam lithography 13
1.3.3 SPM lithography 14
1.3.4 AFM-assisted nanolithography 14
1.3.4.1 Electric-field assisted
oxidation 15
1.3.4.2 Dip-pen nanolithography 17
1.3.4.3 Thermomechanical writing 19
1.3.4.4 Nanofabrication using self assembled monolayer 21
1.3.4.5 Probe assisted patterning using organic resist 22
1.3.4.6 Constructive nanolithography 23
1.3.4.7 Catalytic probe lithography 24
iv
1.4 Scanning Probe Microscopy 24
1.4.1 Scanning tunneling microscope 25
1.4.2 Atomic force microscope 26
1.4.2.1 Basic components of an AFM 27
1.4.2.2 AFM imaging modes 30
1.4.2.3 Lateral force microscopy 33
1.4.2.4 Force curve measurements 34
1.4.2.5 Tip–sample interaction 35

1.5 Applications and challenges of SPM 37
1.6 Nanolithography of Polymer Films 39
1.6.1 Electrostatic nanolithography 40
1.6.2 Chemical nanolithography 40

1.6.3 Electrochemical nanolithography 41
1.7 Strategy and objectives of the work 43
1.8 References 46

Chapter 2. Fabrication of conducting nanopattern
on PVK film using electrochemical Nanolithography

2.1 Introduction 64
2.2 Experimental Section 66
2.2.1 FT-IR measurements 66
2.2.2 Cyclic voltammetry 67
2.3 Results and Discussion 67
2.3.1. Nanopatterning of PVK film on Au (111) 69
2.3.2. Formation of an electrochemical bridge for electropolymerization 70
2.3.3. Conductivity of PVK film on Au (111) substrate 73
2.3.4. Nanopatterning of Carbazole monomer on Si (100) 74
v
2.3.5 Conductive and thermal properties of patterned carbazole film 76
2.3.6. Nanopatterning of PVK film on Si (100) 78
2.3.7 Conductive and thermal properties of patterned PVK film 80
2.3.8. Comparison of PVK and carbazole monomer film patterning 83
2.4 Conclusion 86
2.5 References 88
Chapter 3. Nano/micro scale surface modification
of conjugated precursor polymer film.

3.1 Introduction 92
3.2 Experimental Section 94
3.3 Results and Discussion 95
3.3.1 Nanopatterning of electroactive polymer film 95

3.3.2 Electropolymerization of precursor polymer film 98
3.3.3 Nanowriting on polymer film 100
3.3.4 Electrical conductivity of corona pattern 101
3.3.5 Effect of electron scavenger in pattern formation 102
3.4 Conclusion 106
3.5 References 108
Chapter 4. Fabrication of polymer nanostructures
via electrostatic nanolithography

4.1 Introduction 112
4.2 Experimental Section 113
4.3 Results and discussion 114
4.3.1 Nanopatterning of PMAA film 114
4.3.2 Kinetics and pattern formation of PMAA polymer film 115
vi
4.3.3 Conduction during pattern formation 119
4.4 Conclusion 121
4.5 References 122

Chapter 5. Effect of hydrophobicity on meniscus
formation in nanopatterning of polymer film

5.1 Introduction 126
5.2 Experiments 127

5.3 Results and discussion 128

5.3.1 Patterning of PMA polymer film 129
5.3.2 Patterning of PAA polymer film 132
5.3.3 Hydrophobic effect on patterning 134

5.3.4 Ablation of polymer during patterning 138
5.4 Conclusion 139
5.5 References 141

Chapter 6. Influence of surface properties in
corona pattern formation on polymer films

6.1 Introduction 144

6.2 Experimental Section 145
6.3 Results and Discussion 147
6.3.1 Patterning of aliphatic and aromatic polymer 149
6.3.1.1 Patterning of polyvinylalcohol Vs polyvinylphenol 149
6.3.1.2 Patterning of polymethylmethacrylate Vs polybenzylmethacrylate151
6.3.1.3 Patterning of polyvinylchloride Vs polybenzylchloride 152
6.3.1.4 Patterning of polyvinylacetate Vs polystyrene 154
vii
6.3.1.5 Patterning of polymethacrylate Vs polymethylstyrene 155
6.4 Conclusion 157
6.5. References 158

Chapter 7. Synthesis and nanofabrication of
oligomers using AFM lithography

7.1 Introduction 162
7.2 Experiments 164

7.2.1 Synthesis of triphenylene oligomers 164
7.2.2 Thin film preparation 172
7.2.3 AFM experiment 172

7.3 Results and Discussion 172

7.3.1 Nanofabrication of oligomer 173
7.3.1.1 Patterning of hydrophilic oligomer 1 173
7.3.1.2 Patterning of amphiphilic oligomer 2 175
7.3.1.3 Patterning of amphiphilic oligomer 3 176
7.3.2 Optical properties of the oligomers 178
7.3.3 Transport properties of the oligomers 180
7.4 Conclusion 181

7.5 References 183
Chapter 8. Conclusion and future outlook 186

List of Publications 191


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Fabrication of nanostructure using polymeric materials is a key technique in the
application of organic materials to nanodevices, molecular electronics, and nanosensors.
AFM lithography has been used to manipulate soft materials using biased nano-probe and
it led to the development of surface patterning methodologies at nanoscale. The focus of
this thesis is aimed towards the patterning of various organic surfaces including polymers
and oligomers to develop functional nanostructures using electrochemical and electrostatic
nanolithography. Due to the increasing demand and necessity for the nanoscale fabrication
using organic/polymer materials for organic electronics, we explored here the surface
effects of pattern formation, importance of the water meniscus formation to facilitate
patterning, the choice of method as well as parameter to develop nanostructures and
analyzed their importance. We have explored many polymers with different functional
groups on the polymer backbone, co-polymer, electro-active polymer and oligomers for
the pattern formation and then the physical and chemical properties of the patterns are
investigated. A brief summary of the concepts of nanofabrication, various lithography
technique, atomic force microscope technique and nanolithography of polymer film have

been explained in Chapter One.
In chapter 2, fabrication of nanopatterns with PVK polymer on Au (111) substrate
through elecropolymerization of precursor polymer film was reported. The second part of
this chapter describes the patterning of both carbazole monomer and PVK polymer on Si
(100) substrate and exhibit how the conductive nanopattern can be formed from insulating
polymer through electrochemical nanolithography. Using a voltage-biased atomic force
ix
microscope (AFM) tip, electric-field-induced polymerization through cross-linking of
carbazole moieties were demonstrated with the formation of nanopattern which is
controlled by AFM probe writing speed and bias voltages. Also, the conducting property
(current-voltage (I-V) curves) of these nanopatterns was also investigated using a
conducting-AFM (C-AFM) and the thermal stability of the patterns was evaluated by
annealing the polymer/monomer film above the glass transition (T
g
) temperature of the
precursor polymer.
In chapter 3, we explored the formation of conductive nanopattern from binary
electro active polymer film through electro-oxidation process. In addition to the pattern
formation, corona pattern formation, electric field distribution during pattern formation
and the flow of electron from the tip to the polymer film were analyzed in detail.
In the subsequent chapters, we discuss the patterning of various polymer films and
discussed how the patterning is differentiated with various polymers using electrostatic
nanolithography. In chapter 4, we describe the fabrication of nanostructure from
polymethacrylic acid (PMAA) on Si(100) substrate using electrostatic nanolithography.
The kinetics, growth, and optimization of the conditions such as writing speed and bias
voltages, were investigated for nanopattern formation. The nanostructure of size 28 nm
was created using the biased AFM tip on the PMAA film coated on Si (100) substrate and
found that this method is a direct and reliable method to produce uniform nanostructures
on a polymer film.
The role of water meniscus on the polymer film during the dynamic writing

process is reported in chapter 5. The effect of hydrophobicity on water meniscus
formation between the AFM tip and substrate during the patterning of polymer film were
demonstrated and discuss how such a meniscus formation facilitate the continuous pattern
x
formation on the polymer films. The patterning process was done on a hydrophobic (PMA)
and hydrophilic (PAA) polymer film at various tip speeds and applied biases and the
results were compared to elucidate the surface effect of polymer film for pattern formation.
In chapter 6, we explored the surface effect of corona type patterning formation by
comparing the pattern formation on different polymers such as non-aromatic and aromatic
polymers. Here, we found that polymers with aromatic ring structures facilitate corona
pattern formation as against non-aromatic containing polymers doesn’t show any such
corona pattern other than the dot pattern. The formation of corona pattern attributed to the
combined effect of discharge of electrons between AFM tip and substrate and the electron
rich aromatic/electro active surface groups on the polymer backbone.
Finally, the synthesis and patterning ability of few oligomer molecules with
different functional groups are described in chapter 7. Here we show that functional
groups such as hydrophilic and amphiphillic groups, on the oligomer affects nanopattern
formation. In addition to the patterning, optical and transport properties of ultra thin
organic molecules are explored and the results were discussed.
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13
C-NMR Carbon nuclear magnetic resonance
1
H-NMR Proton nuclear magnetic resonance
2D Two dimensional
AFM Atomic force microscopy
Ar Aromatic
BnBr Benzyl bromide
BuLi Butyl lithium
ca. About
C-AFM Conductive atomic force microscopy
CE Counter electrode
CDCl
3
Deutereochloroform-d
CH
2
Cl
2
Dichloromethane
CH

3
CN Acetonitrile
CHCl
3
Chloroform
CO
2
Me COOCH3
conc. Concentrated
CV Cyclic voltametry
DMF N, N’-Dimethylformamide
DMSO-d
6
Deuterated dimethyl sulfoxide
DPN Dip-pen nanolithography
EBL Electron beam lithography
xii
ECNL Electrochemical nanolithography
EPN Electro pen nanolithography
ESI-MS Electron spray ionization mass spectrum
EUV Extreme ultaviolet
FT-IR Infrared Fouriert transform
F-N Fowler-Nordheim
g Gram(s)
H-bond Hydrogen bonding
HMDS hexamethyldisilazane
hr Hour(s)
Hz Hertz
i.e. That is (Latin id est)
IRRAS IR reflection absorption spectroscopy

ITO Indium tin oxide
I-V Current-voltage
J Coupling constant
K
2
CO
3
Potassium carbonate
LAH Lithium aluminium hydride
LB Langmuir-Blodgett
m Multiplet
m/z Mass/Charge
Maple Matrix-assisted pulsed-laser evaporation
MEK Methyl ethyl ketone
xiii
MeOH Methanol
mg Milligram(s)
ml Milliliter(s)
mmol Milli molar
MOS Metal oxide semiconductor
NMR Nuclear magnetic resonance
PAA Poly(acrylicacid)
PBCl Polybenzylchloride
PBMA Polybenzylmethacrylate
PCZ Polycarbazole
PHC Poly[9-[2-(4-vinylphenoxy)ethyl]-9H-carbazole]
PHT Poly[3-{2-(4-vinylphenoxy)ethyl}thiophene]

PMA Polymethacrylate
PMAA Poly(methacrylic acid)

PMMA Polymethylmethacrylate
PMTC
Poly([3-{2-(4-vinylphenoxy)ethyl}thiophene]-
co-9-[2-(4-vinylphenoxy)ethyl]-9H-carbazole)
PS Polystyrene
PSMe Poly (4-methylstyrene)
PVA Polyvinyl alcohol
PVAc Polyvinyl acetate
PVC Polyvinylchloride
PVK Polyvinylcarbazole
PVPh Polyvinyl phenol
xiv
RE Reference electrode
RPM Redox probe microscopy
SAM Self-assembled monolayer
sec Second
SPL Scanning probe lithography
SPM Scanning probe microscopy
STM Scanning tunnelling microscopy
TBDMS bis(ö-tert-butyldimethyl-iloxyundecyl)disulfide
THF Tetrahydrofuran
T
g
Glass transition temperature
T
m
Melting temperature
WE Working electrode

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Table 6.1 List of polymers, company, molecular weight and their
corresponding solvents to make solution for spin coating of
polymer for patterning.
146
Table 6.2 Chemical structure of the polymers used for patterning 147

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Table 7.1 Kinetics of pattern formation at various voltage with tip speed of
0.1 µm/s. (X Æ denotes no pattern formation was observed)
177
Table 7.2 Optical properties of Oligomer 1,2 & 3 179



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Figure 1.1 Schematic diagram shows the outline of the evolution of electronic
devices from lithographic techniques

6
Figure 1.2 Schematic representation of evolution of top-down and bottom
approach for nanofabrication
10
Figure 1.3 Schematic representation of the nano-oxidation process on Si
substrate.
16
Figure 1.4 Schematic representation of DPN 18
Figure 1.5 Components of a scanning probe instrument 28
Figure 1.6 Beam-deflection set-up for the detection of interacting force in an

AFM
31
Figure 1.7 Distance dependence of Van Der Waals and electrostatic forces
compared to the typical tip-surface separations in the contact mode
(CM), non-contact mode (NCM), and intermittent contact mode
35
Figure 1.8 Chemical lithography of self assembled monolayer of organic
molecules
41
Figure 1.9 schematic representation of the nanopatterning of polymer film by
electrochemical oxidation method
42
Figure 1.10 Flow chart showing the outline of the work done in this thesis 45


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Figure 2.1 (a) Schematic diagram of electrochemical nanolithography (b)
chemical structure and possible polymerization sites of PVK (c)
mechanism for electropolymerization (cationic) and cross-linking
of PVK.
68
Figure 2.2 (a) Three-dimensional nanostructure on the polymer, patterned
using a tip voltage of -7V at a speed of 0.5 µm/s and (b)
nanopattern of lines drawn at varying voltage of -3V to -10V at
constant tip speed of 1 µm/s and the feature size ranging from 35
nm to 150 nm was observed.
For figure a,b), the height profile
below corresponds to the part of the white line marked in the
respective figure above.

69
Figure 2.3 (a) Cyclic voltammogram of PVK in 0.1 M LiClO
4
/ THF solution
(WE: Pt plate, CE: Pt plate, RE: Ag / AgCl) at 1, 5, 10, 15, and 20
cycles at scan rate 50 mV s-1 (b) FT-IR Spectra on ITO substrate.
PVK-spin coated and PVK electrodeposited potentiostatically
(cross-linked).
70
Figure 2.4 (a) Square patterning of PVK surface of 1
µm by
2
electrochemical 74
xvii
oxidation (b) I-V curve measurements of the patterned (i) and
unpatterned area (ii).
Figure 2.5 (a) Nanopatterns drawn on carbazole film at constant bias of -7V
at various tip speed 1 µm/s, 2 µm/s, 4 µm/s, 6 µm/s, 8 µm/s and 10
µm/s corresponds to the line width of 187 nm, 162 nm, 140 nm,
128 nm, 87 nm and 78 nm respectively and imaged by contact
mode AFM (height). (b) 3D image of carbazole monomer
patterned at -7V with a pattern width of 86 nm. Height is at ~ 2
nm.
75
Figure 2.6
(a) Square patterning of size 1 µm
2
on carbazole film at a scanning
speed 1Hz with a tip bias of -5V imaged by contact mode AFM,

and (b) the corresponding current mapping image (C-AFM) of
conductive square pattern with a conducting current of 10.0 pA at
an applied bias of +5V for imaging.
77
Figure 2.7 The AFM height image of the patterned character “NUS” before
(a) and after (b) heating at 270° C for 3 hrs of the carbazole film.
77
Figure 2.8 (a) Nanolines written on PVK film at constant tip speed of 1 µm/s
with the different biases of -5V, -7V, -9V and -11V with line
widths of 83 nm, 128 nm, 162 nm, and 231 nm, respectively, (b)
AFM image with height profile of the pattern “PVK” drawn at -7V
at a tip speed 1 µm/s.
79
Figure 2.9 Variation of pattern width (a) and height (b) with applied bias for
polymer and monomer, (c) Plot of line width Vs AFM tip speed
during PVK and carbazole patterning.
80
Figure 2.10 (a) AFM height images of the electrochemically patterned
polygons at different tip voltages and speeds. (b) Corresponding
C-AFM image of polygon patterning with a conductive current of
10 pA. (c) Square(1 µm
2
) patterning of PVK film at tip scanning
speed of 1Hz with a tip bias of -5V and imaged by contact mode
AFM (d) corresponding I-V curve hysteresis measurements on the
patterned square of the PVK film.
82
Figure 2.11 3D height AFM images of the patterns (a) before and (b) after
heating at a temperature of 270 °C for 3 hrs on PVK polymer film.

83

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3
3
3

Figure 3.1 Electropolymerization of neutral precursor polymer A (PMTC) to
cross-linked conducting polymer B (CPMTC).
93
Figure 3.2 AFM images show (a) the surface morphology of the polymer film
(polymer A) spin coated on the substrate and (b) the thickness
measurement and corresponding height profile. Film thickness was
found to be around 46 nm.
95
Figure 3.3 (a) Dot pattern of polymer (A) film at various bias of -7V. -9V and
-11V with tip contact time of 2s and corresponding diameter of
658 nm, 2778 nm and 5320 nm respectively (b) Line pattern of
polymer A at constant tip speed of 1 µm/s with different applied
97
xviii
voltage of -7V, -9V and -11V. (c) Dot patterns drawn on polymer
film with constant bias of -7V at various tip contact time of 1s, 2s,
4s and 8s and corresponding pattern width of 190 nm, 642 nm, 980
nm, 1990 nm respectively (d) Height image of hexagon pattern of
polymer at -7V with tip speed of 0.5 µm/s, 0.2µm/s and 0.1 µm/s.
Figure 3.4 (a) 3D nanostructure of polymer corona pattern and corresponding
height profile formed at -7V with a tip contact of 5sec (b)
patterning of character “PTC” drawn at -7V with a tip speed of 0.5
µm/s.
100
Figure 3.5 The polymer nanopatterns of the array of dots drawn at constant
voltage of -7V with tip contact time of 1s at each dot.

101
Figure 3.6 (a) Square patterning (1 µm
2
) of polymer A film at a scanning
speed 1 Hz (16 µm/s) with a tip bias of -7V and (b) corresponding
current mapping image of the pattern with a conducting current of
100 pA.
102
Figure 3.7 Schematic representation of electron flow from tip to the polymer
film.
103
Figure 3.8 (a) Dot pattern from a film of polymer A and
perfluoroundecylmethacrylate mixture on Si (100) substrate at -
12V with tip contact time of 12s and diameter of 278 nm (b) dot
patterning at various tip voltage of -7V, -9V, -11V with tip contact
time of 12s on polymer A and pyridine mixture with 1:3 ratio and
(c) (1:5) ratio by volume (d) Morphology of polystyrene film after
attempted square (1µm
2)
) patterning at -12V and tip speed of 2
µm/s with no pattern was observed (e) Morphology of the polymer
A and polystyrene blends coated on Si (100) substrate prior to
patterning (f) Square patterning of polymer blend surface of 5 µm
2

at -9V with a tip speed of 10 µm/s. The patterned area represents
the location of polymer A on the film.
105

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Figure 4.1 a) AFM image of the nanolines drawn with a tip speed of 0.5
µms
-1
at different applied voltages, b) Array of nanopits formed at
-12 V with a diameter of 64 nm and the corresponding height
profile of the pattern.
115
Figure 4.2 a) AFM image of nanodots drawn at -9 V with various bias times
of (going from left to right) 2, 4, 8, 12, and 16 s, and their
corresponding height profile. b) Dependence of pattern width and
depth on applied tip bias and tip speed. The observed feature size
ranges from 35 to 172 nm. c) Array of nanopits patterned at -1.5 V
with a pit width of 28 nm.
116
Figure 4.3 AFM images (above) and height profiles (below) of (a) raised
lines of letters, 78 nm wide, formed at -5 V with a tip speed of 0.5
µms
-1
and (b) grooved patterns, 195 nm wide, drawn at a tip
117
xix
voltage and speed of -12 V and 0.5 µms
-1
, respectively.
Figure 4.4 a) I – V curve of a PMAA film of thickness 60 nm by ramping the
tip to various voltages at a scan rate of 1 Hz and b) the
corresponding raised and grooved patterns.
119

Figure 4.5 I–V curve of polymer films of various thickness: 1) 30 nm, 2) 60
nm, and 3) 110 nm obtained by ramping the tip from -12 to +12 V
at a scan rate of 1 Hz.
120




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5





Figure 5.1 Schematic diagram of AFM lithography method used to pattern
the polymer film.
128
Figure 5.2 AFM height images show the surface morphology of (a) PMA and
(b) PAA polymer film.
129
Figure 5.3 (a) Nanolines drawn on the PMA film at a tip bias of -9V, -10V, -
11V and -12V, with a tip speed of 0.1 µm/s. (b) Continuous,
grooved structure drawn at -12V, at a tip of speed 0.1 µm/s.
130
Figure 5.4 (a) Pentagon pattern drawn on the PMA film at a tip speed of 0.25
µm/s, 0.1 µm/s with tip bias of -12V and (b) array of nanogroove
pattern with size of 108 nm fabricated at -9V with tip contact time
of 2 sec.

131
Figure 5.5 (a) Nanolines written on PAA film at constant tip speed of 0.5
µm/s with different bias of -5V, -7V, -9V and -11V and the
corresponding line widths 35 nm, 59 nm, 117 nm, and 137 nm
respectively, (b) AFM image of square patterning of PPA film

drawn at -7V with a tip speed of 1 µm/s, 0.5 µm/s, 0.25 µm/s and
0.1 µm/s.
133
Figure 5.6 (a) Nano lines of letters “PAA” with 59 nm width formed at tip
bias of -7V and tip speed of 0.5
µm/s and (b) the array of grooved
patterns of 78 nm width drawn on PAA film at a tip voltage of -8V
and tip contact time of 1sec.

134
Figure 5.7 Grooved lines are drawn on the PMA film at various tip speeds
and an applied bias of -12V (a) before and (b) after dipping into
the water. (c) Schematic diagram of water meniscus formation
between the tip and substrate (i) under static condition (ii) during
patterning with applied bias which causes the dissociation of water
meniscus and (iii) meniscus formation on hydrated substrate
during writing.
135
Figure 5.8 Force–distance measurements on polymer film (A) without
applied bias (B) With applied bias (-12V) and (C) After a
successive ramping with applied bias.
137
Figure 5.9 (a) AFM image of PAA film before and (b) after selectively
patterned (i) at a tip bias of -7V and speed of 0.5
µm/s, (ii) at a tip
bias of -11V and speed of 0.05
µm/s, (iii) at a tip bias of -11V and
speed of 0.5
µm/s and the corresponding AFM 3D image. (the sign
(Æ ) indicate the movement of tip on the polymer film)

139
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Figure 6.1 (a) AFM image of surface morphology of polyvinylalcohol (b)
three dimensional (c) height image of the dot patterns drawn on
the polymer film with the applied negative bias of 15V, 20V, 25V
and 35V at a tip contact time of 5 sec and (d) corresponding height
profile of the pattern.
150
Figure 6.2 (a) Height image of surface morphology of polyvinylphenol (b)
height image of the dot pattern drawn on the polymer film with the
applied negative bias of 10V, 12V and 15V at a tip contact time of
5 sec (c) dot pattern drawn at -15V for a tip contact time 3 sec and
(d) corresponding height profile of the pattern.
151
Figure 6.3 (a) AFM Height image of pattern drawn on the PMMA film
surface with the applied bias of -20V and -35V at a tip contact
time of 5 sec (b) corona patterning of PBMA film at a tip bias of -
10V, -15V, and -20V for a tip contact time of 5 sec. Height
profiles of figure (a) and (b) are given below the corresponding
images.
152
Figure 6.4 (a) AFM Height image of pattern drawn on the PVC film surface
with the applied negative bias of 15V, 20V, 25V, 30V and 35V at
a tip contact time of 5 sec (b) corona patterning of PBCl film at a
tip bias -35V for a tip contact time 5 sec. Height profiles of figure
(a) and (b) are given below the corresponding image.

153
Figure 6.5 (a) Height image of pattern drawn on the PVAc film surface with
the applied bias of -15V, -25V and -35V at a tip contact time of 5
sec (b) corona patterning of PS film at a tip bias -15V, -25V and -
35V for a tip contact time 5 sec. Height profiles of figure (a) and
(b) are given below the corresponding image.
154
Figure 6.6 (a) Height image of pattern drawn on the PMA film surface with
the applied bias of 20V, 25V, and 35V at a tip contact time of 5
sec (b) corona patterning of PSMe film at a tip bias 20V, 25V, and
-35V for a tip contact time 5 sec. Height profiles of figure (a) and
(b) are given below the corresponding image.

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Figure 7.1 Triphenylene oligomers
used for patterning 164
Figure 7.2 AFM images shows the surface morphology of the spin coated
oligomers 1 (a) 2 (b) and 3 (c) on a Si (100) surface
173
Figure 7.3 (a) AFM height image of the line pattern drawn on the oligomer 1
with the applied bias of -10V, -15V, -20V and -25V at a tip speed
of 0.1 µm/s and (b) Hexaogonal pattern drawn on the organic film
with the various tip speed of 2 µm/s, 1 µm/s and 0.5 µm/s at an
applied bias of -15V. The corresponding height profile of the
patte
rns are given below the images.
174

Figure 7.4 (a) Height image of the line pattern drawn on the oligomer 2 with 175
xxi
the applied bias of -15V, -20V, -25V and -30V at a tip speed of
0.1 µm/s (b) Hexagon pattern drawn at -30V for a tip speed of 0.1
µm/s and 0.5 µm/s.
Figure 7.5 (a) Height image of the line pattern drawn on the oligomer 3 with
the applied bias of -12V, -15V, -20V, -25V and -30V at a tip speed
of 0.1 µm/s (b) pattern drawn at –various tip speed of 0.5 µm/s,
1.0 µm/s, 2.0 µm/s and 4.0 µm/s with constant applied bias of -
30V. Height profiles of the patterns are shown below the image.
176
Figure 7.6 UV-Vis (a) and emission (b) spectra of the oligomer 1, 2 & 3.

179
Figure 7.7 (a) I-V characteristics of the oligomer 1, 2 and 3 with the
maximum current of 760 pA, 160 pA and 1200 pA respectively
and (b) corresponding F-N plots for the I-V curve.
180

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.
.
.






L
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I
I
I
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T



O
O
O
F
F
F



S
S
S
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H
H
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E
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E
M
M
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E
E
E
S
S
S



P
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a
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g
g
g
e
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e

N
N
N
o
o
o
.
.
.










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Scheme 3.1 Synthetic scheme for the crosslinked homopolymers and co-
polymer from their respective precursors.


99

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Scheme 7.1 Synthesis of oligomers 1, 2 and 3 a) Br

2
, AcOH, 75%; b, f)
BnBr, K
2
CO
3
, EtOH, 90% c) NaOH in abs EtOH, RBr, 60 °C for
10 h, 60%; g) BuLi, Triisopropyl borate, THF, 21%; d, i, h)
Pd(PPh
3
)
4
, toluene, 2M Na
2
CO
3
, 61%; e, j, k) Pd/C, H
2
, THF, 1
drop of conc. HCl.

165


xxiii