Fabrication of nanostructures using atomic force microscope assisted nanolithography 2

Chapter Introduction During the last few decades, a research related to nanoscience and nanotechnology have become one of the most important and exciting forefronts in Physics, Chemistry, Engineering and Biology. It is the science and engineering of making materials, functional structures, and devices at the nanometer scale with a dimensions less than 100 nm by controlling the matter at atomic and molecular dimension.1 Advances in the development of new methods for measuring, manipulating, and constructing objects in the nanoscale dimension provide many opportunities for scientific and technological developments for creating active nanostructures and nanosystems with improved functionality. Identification of the concept of nanotechnology has been attributed to Richard Feynman, who presented a speech in 1959 entitled “There’s Plenty of Room at the Bottom.” In his speech, Feynman predicted manipulating atoms to make materials.2 Although, his bold vision had been considered a bit eccentric at that time, this vision was eventually realized by IBM scientists. The invention of scanning tunneling microscope (STM) microscope (AFM) 3, and atomic force enabled the visualization and then manipulation of atoms and molecules. Later, Eric Drexler stated that nanotechnology would dramatically change the world in the 1980s.1 Nanotechnology attracted interest among scientific and engineering communities, not only as a scientific challenge but also for practical reasons. There have been a number of driving forces facilitating the revolution of nanoscience and nanotechnology. Some of the primary factors which advanced in this field are the need for faster and smaller-scale electronic devices, biochips, and sensors for the fabrication of nano objects or devices. A leap in the data storage industry also helps in the fast advancement of nanoscience and nanotechnology; according to Gordon Moore, co-founder of Intel, the data density would double approximately every 18 months. Moreover the limits of photolithographic process to make computer chips are limited by the diffraction limit of the wavelength of light used to pattern a resist.6 The limitation of current technology warrants new processing methods and protocols. Likewise in biological systems the scientists have studied the basic mechanisms happening for a long time without knowing how and why they work. But the current technological advancement made it easy to mimic the fundamental activities or mechanisms involved in biological systems7 by constructing active nanomachines of living cells, which are chiefly made of proteins. In physics, the wave function of electrons becomes significantly confined when the size of an object approaches atomic dimension. This electron confinement leads to different chemical properties because the quantum mechanical (wavelike) properties of electrons inside matter are strongly influenced by variations on the nanoscale.8-11 However, the observation and manipulation of materials at the atomic scale was not very easy owing to the unavailability of proper technological tools. The invention of the scanning probe microscope (SPM) enabled us to overcome this issue by manipulating materials at the atomic scale.12 AFM is also a key tool for researchers in the fields of bioscience, life science and materials science. In addition, AFM is now used as a tool for the fabrication of nanometer scale features from different materials.13-15 The use of AFM for fabrication of nanostructures from organic/polymer materials is the focus of this thesis. 1.1 Evolution of Nanotechnology Nanotechnology is the term used to cover the design, development and utilization of functional structures with at least one characteristic dimension measured in nanometers.16-17 Though the term nanotechnology is relatively new, the existence of functional devices and structures of nanometer dimension are not new. In the fourth– century AD, glass makers fabricated glasses with nano-sized metals, in particular the Lycurgus cup which now resides in the British museum in London.18 The cup is made from soda lime glass which contained silver and gold nanoparticles. The color of the cup changes from green to deep red when a light source is placed inside due to the presence of metal nanoparticles in the glass.19 In the eighteenth century, the photographic film was developed on a thin layer of gelatin containing silver halide, such as silver bromide, and a base of transparent cellulose acetate.20 The light decomposes the silver halides into nanoparticles of silver which are the pixels of the image.21 Later in 1857, Michel Faraday attempted to explain how metal particles affect the color of church windows.22 However the first explanation for the dependence of color of the glasses on metal size was provided by Gustav Mie.23 Later, in 1960, Richard Feynman, speculated that functional nanoscale devices could be constructed from atomic components. However, it was not before the 1990s that the field of nanotechnology took on as a significant movement.24 Particularly nanostructure characterization was made possible by the invention of scanning probe microscopy. Scanning probe microscopes such as STM, AFM provide imaging and manipulation at the atomic scale and can be used as a characterization tool for highresolution microscopes and nanoindenters.25 At the same time, a rapidly growing level of activity has been directed towards improving the synthesis and assembly of nanoscale building blocks with nanodimensions. Objects at the nanoscale may display physical attributes substantially different from those displayed by either atoms or bulk materials, which may lead to new technological opportunities as well as new challenges.26-28 The dependence of the behavior on the particle sizes can allow one to engineer their properties indicating that this technology has potential to create advances over a wide and diverse range of technological areas.29-33 One good example is increasing the storage capacity in magnetic tapes and provide faster switches for feedback. Thus, the nature of research in nanotechnology is interdisciplinary, covering a wide range of subjects from the chemistry of catalysis in nanoparticles to the physics of quantum dot lasers.34 Researchers in any one particular area need to reach beyond their expertise in order to appreciate the broader implication of nanotechnology and learn how to contribute to this exciting new field. 1.2 Development of Micro and Nanoscale Fabrication Fabrication techniques in the semiconductor industry depend largely on lithographic process to make microelectronic circuits and devices.35-36 The schematic shown in Figure 1.1 explains the necessity of the lithographic process for the evolution of electronic devices. All electronic devices are developed on the semiconducting chip which is essentially built from lithographic process. In the conventional technique, the first step in the nanofabrication process involves the formation of a pattern on the resistive layer on top of a substrate by selectively irradiating with electrons, ions, or photons on the surface followed by a chemical etching. These indirect patterning approaches can compromise the chemical purity of the structure generated and have limitation on type of materials and number of materials that can be patterned. Most of these conventional lithographic methods either break down or poorly controlled when the feature sizes go down to nanometer scale.37 Electronic devices Semiconductor chips Lithography Figure 1.1. Schematic diagram shows the outline of the evolution of electronic devices from lithographic techniques. These drawbacks in the conventional technique lead to the development of new techniques such as direct-write method, where materials can be patterned directly on the substrate at nanoscale. Using this direct write approach, 3D structures can be built directly without the use of masks, allowing for rapid prototyping, product development, and cost effective manufacturing with superior capabilities. But the increased capabilities come with limited flexibility as well as increased complexity, time, and cost. A wide range of direct-write technologies are being developed with approaches to write or transfer patterned materials onto a substrate. Each technique has its own strengths and shortcoming in terms of capabilities such as, resolution, writing speed, 3-dimensional and multimaterial capabilities, operational environment, and the type of final structure to be obtained. Different direct write lithographic techniques which include plasma spray, matrix-assisted pulsed-laser evaporation (MAPLE), laser chemical vapor deposition, micro pen, ink jet printer, scanning probe microscope have been developed.37 These techniques differ in the way that they transfer, deposit or dispense materials for forming nano/micro patterns and they can be compared principally in terms of cost, speed, resolution, and flexibility to work with different materials, final material properties, and processing temperature. Among these techniques, SPM based lithography such as oxidation lithography is regarded as direct write and “resist-free” lithography where a conductive probe is used to provide a local intense electric filed under the vicinity of tip to modify the surface through local anodic oxidation process. 38 Since the invention of scanning probe methods, 38-42 considerable efforts have been undertaken to find methods for manipulating and structuring matter at nano and molecular level. For manipulating matter under ambient conditions or in liquid, scanning probe methods are very convenient. Due to the small size of the probes, which interacts directly with surfaces, a resolution of a few nanometers should be achievable. Furthermore, the nature of the interaction can comprise a multitude of physical and chemical quantities. The scanning-probe-based direct structuring of polymer films has been performed by scratching or indentation experiments.43-47 Local topographical features can also be created by thermo-mechanical writing by using a heated AFM tip for locally melting a polymer substrate.48 -58 The localized deposition of a foreign substance on a surface has been demonstrated with a method called “dip-pen" nanolithography (DPN).59 1.2.1 Necessity of nanoscale fabrication The task of creating devices at the nanoscale requires robust methods for controlled deposition of functional materials on the surface. Nanofabrication can be achieved both by extension of current microfabrication techniques into smaller size regime and by the development of new techniques such as scanning probe microscope patterning. Basic research in nanotechnology should open more potential applications in the semiconductor industry. The conventional lithographic process ranges from current photolithography to next generation lithographies such as extreme ultraviolet lithography,60 -63 electron lithography,64-65 ion lithography66-67 and X-ray lithography.68 It is known that soft X-ray and extreme ultra violet (EUV) lithography employs short wavelength radiation (13 nm) such that normal optical lenses become opaque and an alternative reflective method of focusing and masking must be used. Conventional lithographic methods are still far away from this limit of resolution, the best one being the electron beam lithography process, which achieves a resolution of about to 10 nm. Furthermore, lithographic methods require clean room equipment, vacuum technology, optical systems, etc. and apply only to specific material combinations for the resists, the utilized chemical substances as well as the substrates.69-72 In addition, the down scaling of device dimension due to miniaturization causes the cost of fabrication and processes increases dramatically. Also, there are many basic physics and reliability related issues which demand improved fabrication techniques and smart components for the continued downsizing of electronics devices. For example, the large capacitance and dielectric breakdown in the large electric fields imposed by small lateral dimensions make conventional silicon metal oxide semiconductor (MOS) and biopolar devices impractical. These limitations of existing technique and the current trend of miniaturizing the electronic component has been the driving force for new lithographic techniques in micro/nano technology and nanoelectronics.73-75 The long-term vision is to assemble matter at the atomic scale to obtain full control over the physical and chemical properties of a material. Single atom manipulation is the ultimate limit and it is restricted to specific systems requiring special conditions such as vacuum and low temperatures.76-79 However, in biological systems the build-up of structures on a cellular scale, i.e. in the range of a few micrometers, takes place through self-assembly processes thereby achieving a high degree of order.80-84 It is likely that in the future an important part of micro- and nanostructure techniques will involve ambient liquid environment, which is not compatible with conventional clean room and vacuum techniques. Moreover, these novel techniques based on bottom up processes take advantage of new findings from chemistry, biology and materials science, i.e. they not have to rely only on downscaling of macroscopic techniques.85-87 1.2.2 Nanofabrication Nanostructures can be made in numerous ways. In the broad classification, it divides into either those which build from the “bottom-up”, like atom by atom, or those which construct from the “top-down” using processes that involve the removal or reformation of atoms to create the desired structure.86 These two methods (both top-down and bottom-up) have evolved separately and converge to nanodimensions (figure 1.2). In the bottom-up approach, atoms, molecules and nanoparticles can be used as the building blocks for the creation of complex nanostructures; the useful size of the building blocks depends on the properties to be engineered. By altering the size of the building blocks, controlling their surface functionality, constituents, organization and assembly, it is possible to engineer the properties and functionalities of the nanostructured solids or systems.88-90 Top down Higher performance I µm Micro ele c C nm tronics h ry, P t s i hem s ysic ogy l o i ,B Nanotechnology New functions Bottom up 1960 1970 1980 1990 2000 2010 2020 2030 Figure 1.2. Schematic representation of evolution of top-down and bottom approach for nanofabrication. On the other hand, top-down approaches are inherently simpler and rely either on the removal or division of bulk material, or on the miniaturization of bulk fabrication processes to produce the desired structure with the appropriate properties. Both top-down and bottom-up methods may be viewed as essentially different forms of structural and molecular engineering. Molecular electronics and biomaterials are the two areas that offer the greatest opportunity and challenges for the development, implementation and commercialization of these nanoscale fabrication techniques.91-95 A brief overview of some of the more common fabrication methods using lithographic technique for the fabrication of nanostructures are discussed below. 10 the pattern with increased width of 420 nm and 284 nm, respectively. This result suggests that the amphiphilic oligomer gives high pattern width compared to other molecules. Also the patterning of amphiphilic oligomers and with applied bias of -30V at tip speed of 0.5 µm/s formed the pattern width of 577 nm (figure 7.4b) and 504 nm (figure 7.5b), respectively. Here, the hydrophilic molecule formed thinner patterns at low a voltage whereas amphiphilic oligomer formed thicker patterns. Though the oligomer is amphiphilic, the increased hydrophilic group (OH group) facilitated the patterning with lower pattern width. In addition to the reduction in pattern width, the hydroxyl group also facilitates the patterning ability at lower voltage. The above results suggests that out of three oligomer molecules patterned, oligomer and can be patterned at -10 V and -12 V, whereas in the case of oligomer the patterning starts at a slightly higher voltage of -15 V. This results show the role of hydrophilic molecules in lowering patterning voltage compared to amphiphilic molecules is significant. 7.3.2. Optical properties of the oligomers Understanding the optical properties of the oligomers is important for the application in optoelectronic and organic devices. The absorption and emission spectra of these oligomers 1, & were recorded in solution (THF as solvent). The absorption and emission maxima of the oligomers are summarized in Table 7.2. The hydrophilic oligomer has the absorption maxima of 333 nm whereas the amphilphilic oligomers and showed absorption maximum at 326 nm and 324 nm, respectively, which is characteristic of the optical properties of poly(p-phenylenes).21 178 Table 7.2. Optical properties of Oligomer 1,2 & Optical Properties Oligomer Oligomer Oligomer Absorbance λmax (nm) 333 326 324 Emission λmax (nm) 390 388 384 Optical band gap Eg (eV) 3.73 3.81 3.83 The absorption maxima of the hydriphilic oligomer is red shifted compared to the other amphiphilic oligomers (table 7.2, figure 7.6a). This may be attributed to the ordered structure in solution due to the formation of hydrogen bonding between the hydroxyl groups of adjacent oligomers. The optical band gaps estimated from absorption maxima of the polymers were given in table 7.2 which suggest that the optical band gap is lower (3.73 eV) for the hydrophilic oligomer as compared to amphiphilic oligomer and 3. The emission spectra of the oligomers are depicted in figure 7.6b. The emission properties of oligomer is found to be red shifted compared to the other oligomer molecules and 3. Oligomer Oligomer 300 400 500 WAVE NUMBER(nm) (nm) Wavelength oligomer oligomer oligomer (b) Oligomer EMISSION ABSORBANCE (a) 100 50 400 500 600 Wavelength (nm) Figure 7.6. UV-Vis (a) and emission (b) spectra of the oligomer 1, & 3. 179 7.3.3. Transport properties of the oligomers The characteristic charge transport properties of the oligomers were studied by measuring the I-V curve of thin films coated on Si surface using C-AFM technique. Figure 7.7a shows current-voltage curves of the oligomers 1, & 3. The maximum current of 1200 pA was observed for oligomer at an applied voltage 12V whereas from thin films of oligomer and oligomer 2, this current value was decreased to 760 pA and 160 pA, respectively. The higher current conductivity observed in oligomer films may be due to the presence of multipolar groups compared to other oligomers and the current conductivity increased with increase in number of hydrophilic group (OH-) on the oligomer. Also, the current conductivity increases significantly when the applied voltage is above 4V (figure 7.7a). (a) 600 400 200 200 150 100 50 10 12 (b) 0.8 0.4 0.0 10 12 10 12 VOLTAGE (V) -4 -90 -8 -12 0.4 0.8 1.2 -1 1/V (V ) 1.6 2.0 0.5 1.0 1.5 -1 1/V (V ) 2.0 -60 -50 -30 ln (I/V ) (A/V ) ln (I/V ) (A/V ) 1.2 VOLTAGE (V) VOLTAGE (V) ln (I/V ) (A/V ) CURRENT (nA) CURRENT (pA) CURRENT (pA) 800 -100 -150 -200 0.5 1.0 1.5 2.0 -1 1/V (V ) Figure 7.7. (a) I-V characteristics of the oligomer 1, and 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 The current flow through the organic semiconductor is dictated by tunneling through the barrier present at the electrode and oligomer interface. The field assisted tunneling current are expected to obey the Fowler-Nordheim (F-N) type conduction model.22 The relation between the current density (J) and electric field (E) can be expressed as J/E2 = A exp (-B/E) 22 A and B are constant which can be defined as A = q3/8πhD B = 8π√2m*e D3/2/3hq Where the parameters h, q, D and m*e are plank’s constants, electronic charge, barrier height and effective electronic mass respectively. To verify this, a plot of ln (I/V2) Vs I/V is shown in figure 7.7b for the three oligomers, which shows a linear relationship indicating that it obeys the F-N conduction.23 Higher current conductivities corresponds to easy flow of electrons between the molecules due to the presence of multiple ionizable polar groups. The similar F-N conduction was observed from metal to polymer or other pi-conjugated organic systems.24 7.4 Conclusion A few phenylene oligomers were synthesized and investigated the patterning ability using atomic force microscopy. The patterning of these molecules showed the bias voltage, scanning speed and functional groups were important factors for nanometer-scale lithography of the ultra thin films. The pattern width formation is narrow for hydrophilic oligomer as compared to the amphiphilic oligomer. In addition to reduced pattern formation at low voltage, the hydrophilic oligomer show relatively good conductive and 181 optical properties compared to the amphilphillic oligomers. Exploring the patterning, optical and transport properties of new ultra thin organic molecules is the major advantage as required for potential application of organic nanodevice fabrication. 182 7.5 References 1) (a) Ouyang, J.; Chu, C. W.; Szmanda, C. R.; Ma, L.; Yang, Y. Nat. Mater. 2004, 3, 918. (b) Lee, H. J.; Park, S-M. J. Phys. Chem. B. 2004, 108, 16365. 2) (a) Cravino, A.; Sariciftci, N. C. Nat. Mater. 2003, 2, 360. (b) Bredas, J. R.; Marder, S. Adv. Funct. Mater. 2002, 12, 555. 3) (a) Huynh, W. U.; Dittmer, J. J.; Alivisatos, A. P. Science 2002, 295, 2425. (b) Sun, B.; Marx, E.; Greenham, N. C. Nano Lett. 2003, 3, 961. (c) Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science1995, 270, 1789. 4) (a) Dimitrakopoulos, C. D.; Malenfant, P. R. L. Adv. Mater. 2002, 14, 999. (b) Horowitz, G. 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Phys.2005, 36, 2006. 24) (a) Tu, N. R.; Kao, K. C. J. Appl. Phys. 1999, 85, 7267. (b) Kiy, M.; Biaggio, I.; Koehler, M.; Gunter, P. Appl. Phys. Lett. 2002, 80, 4366. (c) Parker, I. D. J. Appl. Phys. 1994, 75, 1656. 185 Chapter Conclusion and future outlook 186 The prospects of the development of nanoscience and naotechnology largely depend on the ability to fabricate nanostructure on various substrates. The studies carried out in this thesis were aimed to explore various polymers and organic materials to develop AFM based lithographic method to fabricate functional nanostructures. As an alternative tool to conventional lithographic technique, AFM assisted nanolithography offers versatile and powerful method in nanofabrication on a wide variety of materials including insulators, semiconductors, polymers and organic molecules for device fabrication. This thesis is focused towards the fabrication of nanostructures on various polymer and organic films using bias assisted AFM probe which facilitates the formation of nanopattern through physical and chemical process on the polymer film during structure formation. Here, electrostatic nanolithography technique was used to develop nanostructure on insulating polymer film in the first process, and then electrochemical nanolithography was adopted on electroactive polymer at a later stage. The formation of conducting and thermally stable nanopatterns on PVK precursor polymer and carbazole monomer films was demonstrated using a biased AFM tip and the characteristic of these nanopatterns were investigated with respect to the applied bias and tip speed by electrochemical nanolithography. The ability of these precursor polymers and monomers to form conductive patterns with nanometer precision should lead the way to form conductive nanowires/patterns on the insulating film substrates, which can contribute towards the potential advantages in sensors and molecular electronics. In another attempt, patterning of a precursor copolymer with binary electroactive species showed interesting corona pattern formation which depends on the applied voltage and tip speed. The multielectroactive group facilitates the formation of raised structure with corona size distribution and the structure formation can be controlled by patterning 187 bias and probe speed. This method leads to the formation of conductive pattern based on an electropolymerization process and is not simply due to joule heating. Also, the flow of electrons during the patterning can be regulated by the use of polymer blends with electron scavengers on various materials during structure formation. These studies with electrochemical nanolithography will open up the investigation of other precursor polymer materials, electropolymerizable monomers, and electroactive polymers with parameters of patterning related to the Tg of the polymer, electropolymerizability, writing speed, and applied potential. In electrostatic nanolithography process, the nanopatterns were created using biased AFM tip which causes the physical changes on the surface through joule heating of polymer film. Here, various polymers with hydrophilic and hydrophobic functional groups were used for nanopatterning. The kinetics and growth of the nanopatterns were studied by varying the applied voltage, duration of patterning, and speed of the AFM tip. In this approach, a highly versatile direct-write method was developed to produce well-defined nanostructures with a minimum size of 28 nm on a polymer film and demonstrated that the structural characteristics of various polymers play a significant role in patterning. The advancement of AFM nanolithography depends on the effort in understanding the nanofabrication process, which is influenced by many parameters such as water meniscus formation, surface effect, applied bias, chemical composition and humidity of the environment. The development and understanding of these nanofabrication processes is essential to advance the nanolithography process to next level. In this context, we have studied the effect of hydrophobicity/hydrophillicity of the polymer on water meniscus formation between the AFM tip and the substrate. Pattern formation on PMA film can be improved by hydrating polymer surface, which facilitates the formation of the water 188 meniscus during writing process. In another approach, the effect of functional groups on the surface towards the formation of corona pattern was studied. It was found that the polymer with aromatic groups on the backbone gave corona patterns whereas aliphatic polymers without phenyl rings did not exhibit such pattern. Besides polymer film patterning, a series of monomers with multiple functional groups were synthesized and investigated for their patterning ability with respect to the applied voltage between the AFM tip and sample, the scanning speed and the nature of functional group present in the oligomer. Though the functional nanostructure from polymer materials using SPM method can be fabricated, one of the current challenges in the nanotechnology area is the interconnection of nanostructures on semiconducting surfaces. The ability of fabricating conducting nanopattern from non-conducting film lead the way of forming conductive nanowires which can be served to interconnect the functional nanostructure developed on the surface for the potential application in nanodevice fabrication. The high capital and operational cost of conventional nanofabrication process has opened up the way for the development of unconventional techniques such as microcontact printing, nanoimprint lithography and SPM lithography. Among these various techniques, the dual capability, such as molecular visualization and manipulation at nanoscale, of SPM lithography has played a vital role in nanofabrication process. There are many potential opportunities for the application of SPM nanofabrication including fabrication of low-cost organic electronics, tool for biology for investigating individual cells and cell interactions, nanofluidics, NEMS and single-molecule studies, and lithography. One of the draw back of AFM lithography is that it is a serial and slow process 189 which limits its application in industry. Efforts have been made to make parallel array of tips such as millipede technique. Some of the challenges such as understanding the mechanism of structure formation from various materials, chemical characterization of nanoscale structure and ultimate resolution of the pattern formation need to be explored by careful studies. From the perspective of low cost, operational simplicity and advancing scientific investigation, SPL has much promise and open the door to surveying and exploring many areas where high-resolution photolithography and particle-beam writing are not applicable. 190 L LIISST TO OFF PPU UB BL LIIC CA AT TIIO ON NSS R Reeffeerreeeedd JJoouurrnnaallss 1. S. Jegadesan, S. Sindhu, S. Valiyaveettill, Fabrication of Nanostructure on a polymer film using Atomic force microscope, Journal of Nanoscience and Nanotechnology, 2007, 7, 2172-2175. 2. S. Sindhu, S. Jegadesan, Li Hairong, P. K. Ajikumar, M. Vetrichelvan, S. Valiyaveettil, Synthesis and patterning of luminescent CaCO3 – poly (pphenylene) hybrid materials and thin films, Adv. Func. Mater. 2007. (accepted). 3. S. Jegadesan, T. Prasad, S. Sindhu, R. C. Advincula, S Valiyaveettill, Electrochemically Nanopatterned Conducting Coronas of a Conjugated Precursor: SPM Parameters and Polymer Composition, Langmuir, 2006, 22, 3807-3811. 4. S. Jegadesan, S. Sindhu, S. Valiyaveettill, Easy Writing of Nanopatterns on a Polymer Film Using Electrostatic Nanolithography, Small, 2006, 2, 481-484. 5. S. Jegadesan, S. Sindhu, R. C. Advincula, S. Valiyaveettill, Direct Electrochemical Nanopatterning of Polycarbazole Monomer and Precursor Polymer Films: Ambient Formation of Thermally Stable Conducting Nanopatterns, Langmuir, 2006, 22, 780-786. 6. S. Sindhu, S. Jegadesan, R. A. Edward Leong, S.Valiyaveettil, Synthesis of mixed metal carbonates by micellar aggregation, Cryst. Growth & Design, 2006, 6, 15371541. 7. S. Sindhu, S. Jegadesan, A. Parthiban, S. Valiyaveettil, Synthesis and characterization of ferrite nanocomposite spheres from hydroxylated polymers, Journal of Magnetism and Magnetic Materials, 2006, 296, 104-113. 8. S. Jegadesan, R. C. Advincula, S. Valiyaveettil, Nanolithographic electropolymerization of a precursor polymer film to form conducting nanopatterns, Advanced Materials, 2005, 17, 1282-1285. 9. C. Basheer, S. Jegadesan, S. Valiyaveettil, H. K. Lee, Sol-Gel coated oligomers as novel stationary phases for solid phase microextraction, J. Chromatography–A, 2005, 1087, 252-258. 10. S. Sindhu, S. Jegadesan, R. Renu, S. Valiyaveettil, Design of novel nanocomposites through interfacial engineering, J. Meta. and Nanostr. Mater. 2005, 23,327-330. N Noonn--R Reeffeerreeeedd JJoouurrnnaallss 1. S. Jegadesan, S. Sindhu, P. Taranekar, R. C. Advincula, S. Valiyaveettil, Controlled formation of nano- and micro scale structures on polymer films using 191 atomic force microscopy, Polymer Preprints (American Chemical Society, Division of Polymer Chemistry), 2006, 47(2), 374-375. 2. S. Sindhu, S. Jegadesan, L. Hairong, S. Valiyaveettil, Calcium rich biocomposites with tuned optical properties - a polymer driven approach, Polymer Preprints (American Chemical Society, Division of Polymer Chemistry), 2006, 47(2), 326327. 3. S. Jegadesan, R.C. Advincula, S. Valiyaveettil, Electrochemical Nanopatterning of polymer film using atomic force microscope, Proceedings of the International Conference on Nanomaterials, 2005, V1, 359-366. 4. S. Sindhu, S. Jegadesan, B. Vargheese, C. H. Sow, S. Valiyaveettil, Micropatterning of PVK surface by Lase direct, Proceedings of the International Conference on Nanomaterials, 2005, V2, 649-654. 5. S. Sindhu, P.K.Ajikumar, S. Jegadesan, S.Valiyaveettil, Morphology and polymorph selectivity control in calcium carbonate mineralization, Mat. Res. Soc. Symp. Pro. 2005, 847, EE9.38.1 – EE9.38.5. 6. R. Renu, A. Baba, S. Jegadesan, R. C. Advincula, W. Knoll, S. Valiyaveettil, Structure-property investigation of nanorods of amphiphilic poly(P-phenylenes) from collapsed Langmuir monolayers. Polymer Preprints (American Chemical Society, Division of Polymer Chemistry), 2005, 46(1), 560-561. C Coonnffeerreennccee PPrreesseennttaattiioonnss 1. S. Jegadesan, S. Sindhu, S. Valiyaveettil, Nanofabrication of polymer film using conductive probe assisted AFM nanolithography, ICMAT, july 2007, Singapore. (accepted) 2. S. Jegadesan, S. Sindhu, S. Valiyaveettil, Synthesis, characterization and nanofabrication of conjugated oligomers for molecular electronics, ICMAT, july 2007, Singapore. (accepted) 3. S. Jegadesan, S. Sindhu, R. C. Advincula, S. Valiyaveettil, Fabrication of thermally stable and conductive nanopattern on polymer film using Electrochemical nanolithography, 8th International Conference on Nanostructured Materials (NANO 2006), August 20 – 25, 2006, Bangalore, India. 4. S. Jegadesan, S. Sindhu, P. Taranekar, R. C. Advincula, S. Valiyaveettil, Controlled formation of nano- and microstructures on polymer films using atomic force microscopy, 232nd ACS National Meeting, September 10-14, 2006, San Francisco, CA. 5. S. Jegadesan, S. Sindhu, R.C. Advincula, S. Valiyaveettil, Nanopatterning and conductivity studies of the polymer film using atomic force microscopy. NSTI Nanotech 2006, Boston USA. 192 6. S. Jegadesan, S. Sindhu, S. Valiyaveettil, Fabrication of Nanostructure on a polymer film using Atomic force microscope. ICONSAT 2006, New delhi, INDIA. 7. S. Jegadesan, S. Sindhu, R. C. Advincula, S. Valiyaveettil, Nanopatterning of Conjugated Polymer Using Electrochemical Nanolithography, 2nd MRS-S Conference on Advanced Materials. 2006, Singapore. (won the Poster award ) 8. S Jegadesan, S. Valiyaveettil, Synthesis and self-assembly properties of novel terphenylene molecules, International Symposium on Advances in Organic Chemistry (INSOC - 2006), Jan. - 12, 2006, Mahathma Gandhi University, Kerala, India. 9. S. Jegadesan, S. Sindhu, R.C. Advincula, S. Valiyaveettil, “Electrochemical Nanolithography” – Fabrication of thermally stable and conductive nanopattern on polymer film, Singapore International Chemical Conference (SICC-4), Dec – 10, 2005, Singapore. 10. S. Jegadesan, S. Valiyaveettil, Synthesis and self-assembly properties of novel terphenylene molecules, The First Mathematics and Physical Science Graduate Congress, Dec. - 8, 2005, Chulalongkorn University, Bangkok, Thailand. 11. S. Jegadesan, R.C. Advincula, S. Valiyaveettil, Electrochemical Nanopatterning of polymer film using atomic force microscope, NANO 2005, July 2005, India. 12. S. Jegadesan, R.C. Advincula, S. Valiyaveettil, Conductive nanopatterning of polymer film using electrochemical nanolithography, ICMAT, july 2005, Singapore. 13. S. Jegadesan, S. Valiyaveettil, Synthesis and supramolecular nanostructure of novel triphenylene molecules ICMAT, July 2005, Singapore. 14. S. Jegadesan, R. C. Advincula, S. Valiyaveettil, Electrochemical Nanolithography on PVK films using AFM, MRS Fall meeting, 2004, USA. 15. S. Jegadesan, R. C. Advincula, S. Valiyaveettil, Nanopatterns in polymer film by Electrochemical Nanolithography, Japan-Singapore Symposium on Nanoscience & Nanotechnology, 2004, Singapore. 16. S.Jagadesan, S.Valiyaveettil, Supramolecular nanostructured architecture from novel triphenylene oligomers. Nanotech 2004 - 1st International Conference on Nanotechnology, 2004, Singapore. 17. S. Jegadesan, S. Valiyaveettil, Polymer nanopatterning using DPN, Ist NanoEngineering and Nano-Science Congress, 2004, Singapore. 193 [...]... (SAMs) .22 1 -22 4 The role of surface chemical functional groups of the molecules in anodization lithography was studied using the SAMs of 1, 12 - diaminododecane dihydrochloride (DAD.2HCl) and n - tridecylamine hydrochloride (TDA.HCl) as resist molecules .22 5 22 1.3.4.6 Constructive nanolithography The formation of nanostructure through hierarchical construction of self assembled layer using probe-induced... AFM tip .22 6, 22 8 -22 9 An additional molecular layer was deposited ex situ on the oxidized regions by dipping the OTSox patterned surface in a solvent containing the desired molecules Liu et al showed the template guided self-assembly of a water soluble derivative [Au55(Ph2PC6H4SO3Na)12Cl6 ]2 on bilayer patterns with top thiol (–SH) functionality .23 0 -23 1 Besides metallic, semiconductor and organic nanostructures, ... and the simplicity of preparation processes Patterning of these organic thin films is of special importance due to their application as lithographic resists There have been numerous reports describing the SPM based patterning of organic molecular films .21 1 -21 2, 21 6 -22 0 Organic thiol SAM on gold or gallium arsenide substrate have been demonstrated as AFM patternable films213 and SAM of organosilane molecules... effect of atmospheric environment on tip-induced degradation of monlayer was studied In another approach, AFM anodization lithography offers excellent alternative to fabricate highly resolved nanopatterns at high speed through chemical modification of surface Lee et al reported the effect of the surface chemical group on AFM anodization using well-defined self-assembled monolayers (SAMs) .22 1 -22 4 The... axis of the cantilever Therefore, the scan angle must be set to 90°or 27 0° to get a high quality frictional image 1.4 .2. 4 Force curve measurements In addition to topographic measurements, the AFM can also record the amount of force felt by the tip as a function of the separation between the tip and sample A force curve (i.e force- versus-distance curve) can be constructed by monitoring deflection of the... Scanning probe microscope (SPM) lithography is a promising method for fabricating nanostructures using a sharp probe The high resolution pattern formation depends on the tip shape and does not require a high-vacuum system like EBL It has provided a set of tools for the direct nanomanipulation and modification of objects on surfaces Various atomic force microscope (AFM) and scanning tunneling microscope. .. growing Of the many SPMs, AFM is currently the most widely used variant It is the focus of this section 1.4 .2 Atomic force microscope (AFM) AFM was designed to measure the strong short-range repulsive forces between a tip and surface implemented as contact mode imaging The probe (tip) is brought into contact with the surface (hence the name) and repulsive van-der waals forces result in the deflection of. .. advantage of this application is that, fabrication and subsequent imaging can be carried out with the same instrument by just changing parameters of operation 1.4 .2. 1 Basic components of an AFM Detector In order to detect local forces and maintain a narrow spacing, the sharp probe has to be linked to a force sensor which detects the force between the probe and the surface By keeping a constant force between... Lithographic Techniques The invention of new nanofabrication and characterization tools are essential to nanoscience and nanoengineering In fact, the development of nanoscience and nanotechnology has been mainly experimental-driven which is often related with applications of new fabrication and characterization techniques Among the various fabrication techniques, SPM lithography, 38- 42 optical lithography and... electrochemical modification of organic molecules is known as constructive lithography It is a generic chemical approach that combines processes of self-assembly and surface chemical modification with a nondestructive electrochemical patterning technique using conductive AFM tips .22 6 -22 9 This electro-oxidative reaction developed by Sagiv and co-workers converts the terminal methyl group of an OTS-coated silicon . commercialization of these nanoscale fabrication techniques. 91-95 A brief overview of some of the more common fabrication methods using lithographic technique for the fabrication of nanostructures. provided a set of tools for the direct nanomanipulation and modification of objects on surfaces. Various atomic force microscope (AFM) and scanning tunneling microscope (STM) based nanofabrication. advantage of new findings from chemistry, biology and materials science, i.e. they do not have to rely only on downscaling of macroscopic techniques. 85-87 1 .2. 2 Nanofabrication Nanostructures