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 i Dedicated to my parents ii A AC CK KN NO OW WL LE ED DG GE EM ME EN NT TSS 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, Ajikumar, Ms. R. Renu, Ms. J. Akhila, Ms. S. Gayathri Dr. G. A. Rajkumar, Dr. P. K. 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. iii T Taabbllee ooff C Coonntteennttss A Acckknnoow wlleeddggm meennttss iii TTaabbllee ooff ccoonntteennttss iv SSuum mm maarryy ix A Abbbbrreevviiaattiioonnss aanndd SSyym mbboollss xii LLiisstt ooff TTaabblleess xvi LLiisstt ooff FFiigguurreess xvii LLiisstt ooff SScchheem meess xxiii Chapter Introduction 1.1 Evolution of Nanotechnology 1.2 Development of Micro and Nanoscale Fabrication 1.2.1. Necessity of nanoscale fabrication 1.2.2 Nanofabrication 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 80 Conductive and thermal properties of patterned PVK film 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 5.3.4 138 Ablation of polymer during patterning 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 oligomers using AFM lithography nanofabrication 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 Results and Discussion 172 7.3.1 Nanofabrication of oligomer 173 7.3 7.3.1.1 Patterning of hydrophilic oligomer 173 7.3.1.2 Patterning of amphiphilic oligomer 175 7.3.1.3 Patterning of amphiphilic oligomer 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. List of Publications Conclusion and future outlook of 186 191 viii SSuum mm maarryy 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 (Tg) 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. xi A ABBBBR REEVVIIA ATTIIO ON NSS A AN ND D SSYYM MBBO OLLSS 13C-NMR Carbon nuclear magnetic resonance 1H-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 CDCl3 Deutereochloroform-d CH2Cl2 Dichloromethane CH3CN Acetonitrile CHCl3 Chloroform CO2Me COOCH3 conc. Concentrated CV Cyclic voltametry DMF N, N’-Dimethylformamide DMSO-d6 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 K2CO3 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 Tg Glass transition temperature Tm Melting temperature WE Working electrode xv LLIISSTT O OFF TTA ABBLLEESS TTaabbllee N Noo TTiittllee ooff tthhee TTaabbllee PPaaggee N Noo C Chhaapptteerr 66 Table 6.1 Table 6.2 List of polymers, company, molecular weight and their corresponding solvents to make solution for spin coating of polymer for patterning. Chemical structure of the polymers used for patterning 146 147 C Chhaapptteerr 77 Table 7.1 Table 7.2 Kinetics of pattern formation at various voltage with tip speed of 0.1 µm/s. (X Æ denotes no pattern formation was observed) Optical properties of Oligomer 1,2 & 177 179 xvi LLIISSTT O OFF FFIIG GU UR REESS FFiigguurree N Noo TTiittllee ooff tthhee FFiigguurree PPaaggee N Noo C Chhaapptteerr 11 Figure 1.1 Schematic diagram shows the outline of the evolution of electronic devices from lithographic techniques Figure 1.2 Schematic representation of evolution of top-down and bottom approach for nanofabrication Schematic representation of the nano-oxidation process on Si substrate. Schematic representation of DPN Components of a scanning probe instrument Beam-deflection set-up for the detection of interacting force in an AFM 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 Chemical lithography of self assembled monolayer of organic molecules schematic representation of the nanopatterning of polymer film by electrochemical oxidation method Flow chart showing the outline of the work done in this thesis Figure 1.3 Figure 1.4 Figure 1.5 Figure 1.6 Figure 1.7 Figure 1.8 Figure 1.9 Figure 1.10 10 16 18 28 31 35 41 42 45 C Chhaapptteerr 22 Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4 (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. (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 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. (a) Cyclic voltammogram of PVK in 0.1 M LiClO4 / 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). (a) Square patterning of PVK surface of 1µm2 by electrochemical 68 69 70 74 xvii Figure 2.5 Figure 2.6 Figure 2.7 Figure 2.8 Figure 2.9 Figure 2.10 Figure 2.11 oxidation (b) I-V curve measurements of the patterned (i) and unpatterned area (ii). (a) Nanopatterns drawn on carbazole film at constant bias of -7V at various tip speed µm/s, µm/s, µm/s, µm/s, 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 ~ nm. (a) Square patterning of size µm2 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. The AFM height image of the patterned character “NUS” before (a) and after (b) heating at 270° C for hrs of the carbazole film. (a) Nanolines written on PVK film at constant tip speed of 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 µm/s. 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. (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 µm2) 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. 3D height AFM images of the patterns (a) before and (b) after heating at a temperature of 270 °C for hrs on PVK polymer film. 75 77 77 79 80 82 83 C Chhaapptteerr 33 Figure 3.1 Figure 3.2 Figure 3.3 Electropolymerization of neutral precursor polymer A (PMTC) to 93 cross-linked conducting polymer B (CPMTC). AFM images show (a) the surface morphology of the polymer film 95 (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. (a) Dot pattern of polymer (A) film at various bias of -7V. -9V and 97 -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 µm/s with different applied xviii Figure 3.4 Figure 3.5 Figure 3.6 Figure 3.7 Figure 3.8 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. (a) 3D nanostructure of polymer corona pattern and corresponding 100 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. The polymer nanopatterns of the array of dots drawn at constant voltage of -7V with tip contact time of 1s at each dot. (a) Square patterning (1 µm2) of polymer A film at a scanning speed 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. Schematic representation of electron flow from tip to the polymer film. (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 (1µm2) ) patterning at -12V and tip speed of 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 µm2 at -9V with a tip speed of 10 µm/s. The patterned area represents the location of polymer A on the film. 101 102 103 105 C Chhaapptteerr 44 Figure 4.1 Figure 4.2 Figure 4.3 a) AFM image of the nanolines drawn with a tip speed of 0.5 115 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. a) AFM image of nanodots drawn at -9 V with various bias times 116 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. AFM images (above) and height profiles (below) of (a) raised 117 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 xix Figure 4.4 Figure 4.5 voltage and speed of -12 V and 0.5 µms-1, respectively. a) I – V curve of a PMAA film of thickness 60 nm by ramping the 119 tip to various voltages at a scan rate of Hz and b) the corresponding raised and grooved patterns. I–V curve of polymer films of various thickness: 1) 30 nm, 2) 60 120 nm, and 3) 110 nm obtained by ramping the tip from -12 to +12 V at a scan rate of Hz. C Chhaapptteerr 55 Figure 5.1 Figure 5.2 Figure 5.3 Figure 5.4 Figure 5.5 Figure 5.6 Figure 5.7 Figure 5.8 Figure 5.9 Schematic diagram of AFM lithography method used to pattern the polymer film. AFM height images show the surface morphology of (a) PMA and (b) PAA polymer film. (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. (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 sec. (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 µm/s, 0.5 µm/s, 0.25 µm/s and 0.1 µm/s. (a) Nano lines of letters “PAA” with 59 nm width formed at tip bias of -7V and tip speed of 0.5µm/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. 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. Force–distance measurements on polymer film (A) without applied bias (B) With applied bias (-12V) and (C) After a successive ramping with applied bias. (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) 128 129 130 131 133 134 135 137 139 xx C Chhaapptteerr 66 Figure 6.1 Figure 6.2 Figure 6.3 Figure 6.4 Figure 6.5 Figure 6.6 (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 sec and (d) corresponding height profile of the pattern. (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 sec (c) dot pattern drawn at -15V for a tip contact time sec and (d) corresponding height profile of the pattern. (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 sec (b) corona patterning of PBMA film at a tip bias of 10V, -15V, and -20V for a tip contact time of sec. Height profiles of figure (a) and (b) are given below the corresponding images. (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 sec (b) corona patterning of PBCl film at a tip bias -35V for a tip contact time sec. Height profiles of figure (a) and (b) are given below the corresponding image. (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 sec (b) corona patterning of PS film at a tip bias -15V, -25V and 35V for a tip contact time sec. Height profiles of figure (a) and (b) are given below the corresponding image. (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 sec (b) corona patterning of PSMe film at a tip bias 20V, 25V, and -35V for a tip contact time sec. Height profiles of figure (a) and (b) are given below the corresponding image. 150 151 152 153 154 155 C Chhaapptteerr 77 Figure 7.1 Figure 7.2 Figure 7.3 Figure 7.4 Triphenylene oligomers used for patterning AFM images shows the surface morphology of the spin coated oligomers (a) (b) and (c) on a Si (100) surface (a) AFM height image of the line pattern drawn on the oligomer 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 µm/s, µm/s and 0.5 µm/s at an applied bias of -15V. The corresponding height profile of the patterns are given below the images. (a) Height image of the line pattern drawn on the oligomer with 164 173 174 175 xxi Figure 7.5 Figure 7.6 Figure 7.7 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. (a) Height image of the line pattern drawn on the oligomer with 176 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. UV-Vis (a) and emission (b) spectra of the oligomer 1, & 3. 179 (a) I-V characteristics of the oligomer 1, and with the 180 maximum current of 760 pA, 160 pA and 1200 pA respectively and (b) corresponding F-N plots for the I-V curve. xxii SScchheem mee N o . No. LLIISSTT O OFF SSC CH HEEM MEESS PPaaggee N Noo C Chhaapptteerr 33 Scheme 3.1 Synthetic scheme for the crosslinked homopolymers and copolymer from their respective precursors. 99 C Chhaapptteerr 77 Scheme 7.1 Synthesis of oligomers 1, and a) Br2, AcOH, 75%; b, f) BnBr, K2CO3, EtOH, 90% c) NaOH in abs EtOH, RBr, 60 °C for 10 h, 60%; g) BuLi, Triisopropyl borate, THF, 21%; d, i, h) Pd(PPh3)4, toluene, 2M Na2CO3, 61%; e, j, k) Pd/C, H2, THF, drop of conc. HCl. 165 xxiii [...]... Figure 1.2 Schematic representation of evolution of top-down and bottom approach for nanofabrication Schematic representation of the nano-oxidation process on Si substrate Schematic representation of DPN Components of a scanning probe instrument Beam-deflection set-up for the detection of interacting force in an AFM Distance dependence of Van Der Waals and electrostatic forces compared to the typical tip-surface... Schematic diagram of electrochemical nanolithography (b) chemical structure and possible polymerization sites of PVK (c) mechanism for electropolymerization (cationic) and cross-linking of PVK (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... 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 (a) 3D nanostructure of polymer corona pattern and corresponding 100 height profile formed at -7V with a tip contact of 5sec (b) patterning of character... at -7V with a tip speed of 0.5 µm/s The polymer nanopatterns of the array of dots drawn at constant voltage of -7V with tip contact time of 1s at each dot (a) Square patterning (1 µm2) 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 Schematic representation of electron flow from... of 15V, 20V, 25V and 35V at a tip contact time of 5 sec and (d) corresponding height profile of the pattern (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... corresponding height profile of the pattern (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 (a) AFM Height image of pattern drawn on the PVC... nanolines drawn with a tip speed of 0.5 115 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 a) AFM image of nanodots drawn at -9 V with various bias times 116 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... to 172 nm c) Array of nanopits patterned at -1.5 V with a pit width of 28 nm AFM images (above) and height profiles (below) of (a) raised 117 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 xix Figure 4.4 Figure 4.5 voltage and speed of -12 V and 0.5 µms-1, respectively a) I – V curve of a PMAA film of thickness 60 nm... 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 (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... time of 2 sec (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 (a) Nano lines of letters “PAA” with 59 nm width formed at tip bias of -7V . 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. FABRICATION OF NANOSTRUCTURES USING ATOMIC FORCE MICROSCOPE ASSISTED NANOLITHOGRAPHY SUBBIAH JEGADESAN M. Sc.,(Madurai. 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