CHEMICAL GROWTH ROUTES TO GRAPHENE AND GRAPHENE APPLICATIONS ANG KAILIAN PRISCILLA NATIONAL UNIVERSITY OF SINGAPORE 2012     CHEMICAL GROWTH ROUTES TO GRAPHENE AND GRAPHENE APPLICATIONS ANG KAILIAN PRISCILLA B.Sc (Hons) National University of Singapore A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY NUS GRADUATE SCHOOL FOR INTEGRATIVE SCIENCES AND ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2012     Declaration I hereby declare that this thesis is my original work and it has been written by me in its entirety. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has also not been submitted for any degree in any university previously. _____________________ Ang Kailian Priscilla 17 September 2012 I    Acknowledgements This dissertation would not have been possible without the opportunity given to me by the NUS Graduate School for Integrative Sciences and Engineering (NGS) and the constant support and inspiration bestowed to me by the following people: My principle supervisor, Professor Loh Kian Ping, has always been an earnest motivator and educator ever since I joined his research group in 2006 during my undergraduate studies in NUS. His philosophy in doing good science, critical thinking skills and passion for research are inspiring. He never fails to provoke our thoughts to think deeper and think outside the box. He exudes the true spirit of a scientist, a fighter - constantly asking questions, constantly seeking answers, constantly displaying a never-say-die attitude. His accolades in the research and education sector are widely recognised and it is truly a privilege to be under his supervision. My co-supervisor, Associate Professor John Thong, never fails to provide useful solutions and insights to problems pertaining to semiconductor device fabrication and characterisation. He always avails himself to students on a weekly basis to provide timely advice on our work and to brainstorm for plausible solutions. My collaborator, Associate Professor Thorsten Wohland, has always been patient in explaining the principles behind state-of-the-art fluorescence techniques with great enthusiasm. His enthusiasm for research rubs off on me when he cosupervised me for my undergraduate final year project in 2007/2008. Collaborating with him again for my Ph.D research work has been an enjoyable journey. My collaborator, Professor Lim Chwee Teck, is an epitome of an admirable and amicable educator, one who listens to students and provides useful advice, not II    just in their research endeavours but also in their personal lives – a holistic approach to the development of an individual. His passion in the biomedical research and translation of its fruits to useful devices for clinical applications inspires me to strive towards the goals of real life application for my research My heartfelt thanks extend to the colleagues in Graphene Research Centre, Centre for Integrated Circuit Failure Analysis & Reliability (CICFAR), Biophysical Fluorescence Laboratory, Infectious Diseases unit and BioSystems and Micromechanics unit under the Singapore-MIT Alliance for Research & Technology (SMART). I would like to give special thanks to Miss Goh Bee Min, Dr. Lu Jiong, Miss Lena Tang, Miss Candy Lim, Dr. Wang Shuai, Dr. Bao Qiaoliang, Dr. Wang Yu, Dr. Zhang Huijuan, Dr. Hao Yu Feng, Dr. Wang Ziqian, Dr. Wang Rui, Miss Liu Dan, Miss Meng Lei, Mrs Ho Chiow Mooi, Mr. Koo Chee Keong, Mr. Jagadish Sankaran, Dr. Li Ang, Dr. Hou Han Wei and Miss Xu Xiaofeng. I am eternally grateful for the unending love of my husband, Brandon Koh. Despite having a workaholic wife like me, he never fails to surprise me with little acts of love and acts of service. I have the best parents ever. Without their steadfast love, I would never become who I am today. I have a great sister, who always gives me refreshment courses on integration and partial differentiation, matrices and statistics. I am thankful for my parent-in-laws for their constant support. I can never without my best friends. This is not an oxymoron but I have two extremely wonderful and God-sent angels, Annie Chan and Chia Poju. Their hugs, advice and words of wisdom are carved in my heart for keep. Finally, I am blessed to have two wonderful mini schnauzers, one cute poodle and four lovely Siberian hamsters which provide some form of welcome distraction and relief from my work. III    List of Publications 1. Ang, P. K.; Li, A.; Jaiswal, M.; Wang, Y.; Hou, H. W.; Thong, J. T.; Lim, C. T.; Loh, K. P., Flow sensing of single cell by graphene transistor in a microfluidic channel. Nano Lett 2011, 11, 5240-5246. 2. Ang, P. K.; Jaiswal, M.; Lim, C.; Wang, Y.; Sankaran, J.; Li, A.; Lim, C. T.; Wohland, T.; Barbaros, O.; Loh, K. P., A Bioelectronic Platform Using a Graphene-Lipid Bilayer Interface. Acs Nano 2010, 4, 7387-7394. 3. Wang, S.; Ang, P. K.; Wang, Z. Q.; Tang, A. L. L.; Thong, J. T. L.; Loh, K. P., High Mobility, Printable, and Solution-Processed Graphene Electronics. Nano Letters 2010, 10, 92-98. 4. Ang, P. K.; Wang, S.; Bao, Q. L.; Thong, J. T. L.; Loh, K. P., HighThroughput Synthesis of Graphene by Intercalation - Exfoliation of Graphite Oxide and Study of Ionic Screening in Graphene Transistor. Acs Nano 2009, 3, 3587-3594. 5. Ang, P. K.; Loh, K. P.; Wohland, T.; Nesladek, M.; Van Hove, E., Supported Lipid Bilayer on Nanocrystalline Diamond: Dual Optical and Field-Effect Sensor for Membrane Disruption. Advanced Functional Materials 2009, 19, 109-116. 6. Ang, P. K.; Chen, W.; Wee, A. T. S.; Loh, K. P., Solution-Gated Epitaxial Graphene as pH Sensor. Journal of the American Chemical Society 2008, 130, 14392-14393. 7. Wang, Y.; Lee, W. C.; Manga, K. K.; Ang, P. K.; Liu,Y. P.; Lim, C. T.; Loh, K. P., Fluorinated Graphene for Promoting Neuro-Induction of Stem Cells. Advanced Materials 2012, 24, 4285-4290. IV    8. Cole, D. J.; Ang, P. K.; Loh, K. P., Ion Adsorption at the Graphene/Electrolyte Interface. The Journal of Physical Chemistry Letters 2011, 1799-1803. 9. Polavarapu, L.; Manga, K. K.; Yu, K.; Ang, P. K.; Cao, H. D.; Balapanuru, J.; Loh, K. P.; Xu, Q. H., Alkylamine capped metal nanoparticle "inks" for printable SERS substrates, electronics and broadband photodetectors. Nanoscale 2011, 3, 2268-2274. 10. Hu, M.-S.; Kuo, C.-C.; Wu, C.-T.; Chen, C.-W.; Ang, P. K.; Loh, K. P.; Chen, K.-H.; Chen, L.-C., The production of SiC nanowalls sheathed with a few layers of strained graphene and their use in heterogeneous catalysis and sensing applications. Carbon 2011, 49, 4911-4919. 11. Zhao, M.; Wang, S.; Bao, Q. L.; Wang, Y.; Ang, P. K.; Loh, K. P., A simple, high yield method for the synthesis of organic wires from aromatic molecules using nitric acid as the solvent. Chemical Communications 2011, 47, 41534155. 12. Lim, C. X.; Hoh, H. Y.; Ang, P. K.; Loh, K. P., Direct Voltammetric Detection of DNA and pH Sensing on Epitaxial Graphene: An Insight into the Role of Oxygenated Defects. Analytical Chemistry 2010, 82, 7387-7393. 13. Loh, K. P.; Bao, Q. L.; Ang, P. K.; Yang, J. X., The chemistry of graphene. Journal of Materials Chemistry 2010, 20, 2277-2289. 14. Pachoud, A.; Jaiswal, M.; Ang, P. K.; Loh, K. P.; Ozyilmaz, B., Graphene transport at high carrier densities using a polymer electrolyte gate. Epl 2010, 92. 15. Midya, A.; Mamidala, V.; Yang, J. X.; Ang, P. K. L.; Chen, Z. K.; Ji, W.; Loh, K. P., Synthesis and Superior Optical-Limiting Properties of Fluorene- V    Thiophene-Benzothiadazole Polymer-Functionalised Graphene Sheets. Small 2010, 6, 2292-2300. 16. Chong, K. F.; Loh, K. P.; Ang, K.; Ting, Y. P., Whole cell environmental biosensor on diamond. Analyst 2008, 133, 739-743. VI    Table of Contents Declaration . I Acknowledgements . II List of Publications . IV Table of Contents VII Summary XII List of Tables XIV List of Figures . XV List of Abbreviations and Symbols XXV PART I BASIC ASPECTS Chapter 1: Introduction 1.1. An introduction to carbon materials . 1.2. Background on graphene 1.2.1. Unique structure and properties of graphene 1.2.2. Synthesis routes to graphene . 1.3. Graphene as a transducer in field-effect transistor (FET) sensor 11 1.4. Overview of objectives and work scope 13 1.5. References 15 Chapter 2: Literature Review 2.1. Principles of FET sensors . 23 2.1.1. Basic operation of FET sensors . 23 2.1.2. Working principles of back-gated and electrolytically top-gated FET sensors . 26 2.1.3. Comparisons between back-gated and electrolytically top-gated FET sensors 29 2.2. Bioelectronic applications of graphene FET (GFET) 31 2.2.1. Deoxyribonucleic acid (DNA)-based GFET . 32 VII    2.2.2. Protein-based GFET 36 2.2.3. Cell-based GFET . 37 2.3. Summary and outlook 39 2.3.1. Key challenges for the development of GFET sensors . 39 2.3.2. Outlook 41 2.4. References 42 Chapter 3: Experimental Techniques 3.1. Introduction 48 3.2. Spectroscopy 48 3.2.1. Raman spectroscopy 49 3.2.2. Ultraviolet-visible spectroscopy 51 3.2.3. X-ray photoelectron spectroscopy (XPS) 54 3.2.4. Fluorescence correlation spectroscopy (FCS) . 56 3.3. Microscopy . 58 3.3.1. Atomic force microscopy (AFM) 58 3.3.2. Scanning electron microscopy (SEM) . 60 3.3.3. Total internal reflection fluorescence microscopy (TIRFM) 61 3.3.4. Differential interference contrast (DIC) microscopy 63 3.4. Lithography 65 3.4.1. Optical lithography 66 3.4.2. Electron beam lithography (EBL) . 68 3.5. Microfluidic flow cytometry 70 3.6. References 73 PART II CHEMICAL ROUTES TO EXFOLIATED GRAPHENE SHEETS Chapter 4: High-Throughput Synthesis of Graphene by Intercalation-Exfoliation of Graphite Oxide and Study of Ionic Screening in Graphene Transistor 4.1. Introduction 76 4.2. Materials and methods . 78 VIII    The forces are generally electrostatic in nature. In order to increase the sensitivity, the tip is made to vibrate close to its resonant frequency. This mode is now termed as tapping mode. Variations in tip-sample distances and hence forces will alter the resonant frequency of the tip. The changes in resultant frequency, which correlate to the magnitude of forces in action, will be used to generate the topographic image of the sample. 3.3.2. Scanning electron microscopy (SEM) Scanning electron microscopy (SEM) relies on a beam of high-energy electrons, which scans a surface in a raster fashion, to generate information of the sample such as surface topography, chemical composition, crystalline structure and orientation. Figure 3.8. Schematic representation of the instrumentation of scanning electron microscopy. 60    Figure 3.8 shows a typical setup for SEM. An electron beam emitted from an electron gun is focused by a series of condenser lens and made to deflect in the x and y axes so that it scans the sample surface in a raster fashion. When the electron beam hits the sample, it penetrates the sample and creates an electron-sample interaction volume shaped like a tear-drop beneath the sample surface. Energy exchange occurs when the incident electron beam collides with the sample, giving rise to primary backscattered electrons which are reflected from the sample by elastic scattering, secondary electrons by inelastic scattering, Auger electrons, characteristic X-rays, cathodoluminescence and specimen current; each of which are detected by specialised detectors. While secondary electrons give information of the morphology and topography of samples and back-scattered electrons illustrate contrasts in composition of multi-phase samples, X-rays can be used for elemental analysis. With a narrow electron beam and large depth of field, SEM can be routinely used to acquire high definition and three dimensional images of samples. 3.3.3. Total internal reflection fluorescence microscopy (TIRFM) Total internal reflection fluorescence microscopy (TIRFM) utilises an induced evanescent field, which undergoes exponential intensity decay with increasing distance from the surface, to selectively excite fluorescent molecules immediately adjacent to a glass-water or glass-buffer interface (Figure 3.9). 61    Figure 3.9. (a) Schematic representation of the concept of total internal reflection fluorescence microscopy depicting the selective excitation of fluorescent molecules in a cell membrane of a living cell resting on a glass slide. (b) Exponential intensity decay of the evanescence field at the glass-buffer interface. Copyright (2012) Olympus America Inc. To understand TIRFM, it is necessary to discuss the Snell’s Law, in which light passing between two media of different refractive index is either refracted as it enters the second medium or reflected at the interface. This relationship is given by: n1 • sin θ = n • sin θ (Equation 3.6) Where θ is the angle between the incident wave and the normal in the medium of higher refractive index n1 and θ is the angle of refracted wave at the interface into the medium of lower refractive index n2. As the incident angle θ relative to the normal increases beyond the critical angle, where the refraction angle θ is 90o, a vast majority of light is completely reflected at the interface, leaving a small proportion of it penetrating through the interface and creating an electromagnetic field (called the evanescent field) in the medium of lower refractive index n2. Owing to the exponential decay of evanescent field intensity, fluorescent molecules far away from the surface will not be excited. This greatly reduces undesirable secondary fluorescence emission from molecules not in the primary focal plane and significantly 62    increases the signal-to-background ratio as compared to classical widefield techniques. Therefore, the combined use of TIRFM and FCS is frequently used to study the interfacial relationship between molecules and surfaces, which provides fundamental understanding to biological processes. The interfacial relationship between supported lipid bilayers and graphene can be studied in this manner. Being atomically thin and optically transparent, graphene does not cause significant attenuation to the evanescent field generated. Graphene simply changes the critical angle needed to achieve total internal reflection since the refractive index of graphene is higher than glass.14 3.3.4. Differential interference contrast (DIC) microscopy Differential interference contrast (DIC) microscopy is particularly useful to image living cells and unstained, transparent specimens which are difficult to observe under traditional brightfield illumination. Although phase contrast could be used to image these specimens, undesirable halo artifacts are often observed. Therefore, DIC was invented to detect optical gradients in specimens and convert them into intensity differences.15 A good demonstration of the apt use of DIC visualisation is shown in Section 7.3.3. Unaffected by the presence of graphene due to its optical transparency, the morphological differences between healthy red blood cells and malaria infected cells flowing across the graphene surface are clearly distinguishable with DIC without the need for fluorescence labelling. 63    Figure 3.10. Schematic illustration of the microscope configuration for differential interference contrast. Light is polarised in a single vibration plane by the polariser before entering the lower Wollaston prism that acts as a beam splitter. Next, light passes through the condenser and sample before the image is reconstructed by the objective. Above the objective, a second Wollaston prism acts as a beam-combiner and passes the light into the analyser where it interferes constructively and destructively. For DIC, the polarised light microscope is modified with two Wollaston prisms, one to the front focal plane of the condenser and another at the rear focal plane of the objective (Figure 3.10). When the plane polarised light, vibrating in one direction perpendicular to the propagating direction of light beam enters the first Wollaston prism, it is split into two parallel rays, vibrating perpendicular to each other. These rays intersect at the front focal plane of the condenser and travel extremely 64    close together with a slight path difference. The split beams then pass through the specimen where their wave paths are altered differently depending on the thickness and refractive indices of different segments of the specimen. As the two parallel beams enter the objective, they are focused above the rear focal plane. Here, they enter the second Wollaston prism which combines the two beams and removes the original path difference induced. However, having traversed the specimen at differing areas, the path lengths of the two parallel beams are no longer the same. In order to bring these two vibrating beams onto the same plane and axis for interference to occur, they are made to pass through a second analyser (polariser) above the Wollaston beam-combining prism. This light then enters the eyepiece where differences in intensity and colour corresponding to the specimen can be observed. The colour and intensity effects are related to the rate of change in refractive index and/or specimen thickness. Although a pseudo three-dimensional appearance of the specimen is formed, it does not represent the true geometric nature of the specimen and hence DIC images are not suitable for accurate measurement of heights and depths. 3.4. Lithography The general working principle of lithography is to use chemical reactions to create an image. Two methods are commonly employed for microscale or nanoscale device fabrication in the semiconductor industry, namely optical and electron beam lithography. 65    3.4.1. Optical lithography Optical lithography is a lithographic process that utilises visible or UV light to transfer a geometric pattern from a photomask to a light-sensitive photoresist coated on a substrate. The photomask is typically a fused quartz substrate with patterns defined by a layer of chrome, such that only regions which are not covered by chrome allow light to pass through. There are two types of resists, namely positive and negative. Positive resists contain a resin and a photoactive compound; the latter being an inhibitor of dissolution in the developer. Upon exposure to UV light, the photoactive dissolution inhibitor is destroyed, making the resin soluble in the developer. Therefore, a positive photoresist transfers a positive image of the mask pattern onto the substrate. On the other hand, negative resists contain a chemically inert rubber and a photoactive agent. Upon exposure to UV light, cross-linking between the photoactive agent and rubber is initiated, making the resultant UVexposed polymer less soluble in the developer. As a result, a negative image of the mask pattern is transferred onto the substrate. 66    Figure 3.11. Standard operating procedure for optical lithography. The standard operating procedure for optical lithography is illustrated schematically in Figure 3.11 and is further elaborated as follows:  Substrate preparation. Substrates should be free of organic contamination and excessive physically adsorbed moisture. Substrates are typically cleaned in acetone followed by isopropyl alcohol (IPA) with sonication.  Spin-coating and soft bake. An approximately one-nanometre to fewnanometres thick photoresist is deposited onto a cleaned substrate via spin coating. The resist-coated substrate is then prebaked to remove excess photoresist solvent. 67     Exposure. A photomask is aligned using a mask aligner to position its desired orientation above the resist-coated substrate. The photoresist is then exposed to a pattern of light, typically in the UV region, through the photomask. A resultant latent image of the mask may be visible after UV exposure.  Post-exposure bake. An optional step called post-exposure bake may be performed before development to quench standing waves especially for a highly reflective substrate. Standing waves are produced when coherent monochromatic light reflected from a substrate interferes with the incident light and these standing waves are responsible for the characteristic “scalloped” patterns observed after development.  Development. After exposure, the substrate is exposed to the developer. Mild agitation of the substrate or pumping of the developer should be used to ensure uniform development.  Hard bake. The polymer-patterned substrate may be hard-baked to improve stability, adhesion, and plasma and chemical resistance of the polymer layer for substrate processing by metallisation, ion implantation, wet chemical or plasma etching. 3.4.2. Electron beam lithography (EBL) Electron beam lithography (EBL) is a lithographic process that uses a focused electron beam to create nanometre-sized patterns on substrates covered with a layer of electron-sensitive resist. Unlike optical lithography which requires a photomask to project patterns onto the substrate, EBL does not require any mask since the 68    movement of the electron beam is solely controlled by the writing software. Therefore, a typical EBL system is a combination of SEM, comprising an electron gun that supplies electrons, an electron column that shapes and focuses the electron beam, a deflection system to raster the electron beam according to the pattern intended and a mechanical stage to position the substrate under the electron beam, with an additional computer system that establishes communication between the SEM and the writing software. Because the wavelengths of electrons are shorter than UV-visible light, EBL is capable of producing higher patterning resolution in the nanometre range. Figure 3.12. Schematic representation of electron beam lithography using a positive resist. Similar to optical lithography, EBL involves the usage of positive and negative resists. When exposed to electron bombardment, positive resist undergoes bond breaking, known as a chain-scission reaction, and the exposed regions become more soluble in the developer. As a result, an identical image to that drawn by the electron beam is left on the polymer-coated substrate (Figure 3.12). Conversely, negative resist produces a reversed image since the regions exposed to electron beam undergo a cross-linking reaction, making these regions less soluble in the developer. 69    Figure 3.13. Monte Carlo simulation of electron trajectories of 100 electrons at (a) 10 kV and (b) 20 kV in PMMA film. Reproduced with permission from ref.9. Copyright (1975) American Institute of Physics. Although EBL is capable of delivering feature sizes in the nanometre range, the resultant patterns are usually wider than intended due to electron-solid interactions (Figure 3.13).16, 17 As electrons penetrate the resist, collision of primary electrons with matter results in small angle scattering events (forward scattering) as well as large angle scattering events (backscattering), both of which create a wider beam profile at the bottom of the resist than at the top, resulting in additional resist exposure. As the primary electrons exchanged energy with the resist, secondary electrons are produced. Although secondary electrons are responsible for the main process of resist exposure, they contribute further to the widening of the electron beam diameter, culminating to a minimum practical resolution of 20 nm. 3.5. Microfluidic flow cytometry Flow cytometry is a process that quantifies and measures the physical and/or chemical characteristics of biological entities or non-biological particles as they pass 70    through a detector in a fluid stream.18 Therefore, it typically consists of a flow cell for particle manipulation in a fluid stream and an optical19 or electrical20 detector for particle analysis. Since its conception in 1940s, flow cytometry has become an indispensible tool in clinical laboratories, capable of counting and detecting viruses, bacteria and diseased mammalian cells for the diagnosis and prognosis of diseases.21 Although conventional flow cytometers are mature tools for high-throughput screening, the bulky operating units and the requirement for large sample volumes limit its widespread applications in the biomedical and analytical fields. A promising branch of fluid mechanics operating in the micrometre scale is microfluidics, which deals with the precise manipulation of fluidic behaviours in a geometric confinement of a few micrometres. The flow of a fluid through a microfluidic channel can be characterised by the Reynolds number, Re, given by: Re  LVavg   (Equation 3.7) Where L = 4A/P, with A being the cross sectional area of the channel and P being the wetted perimeter of the channel, µ is the fluid viscosity, ρ is the fluid density and Vavg is the average flow velocity. Due to the small dimension of microfluidic channel, Re is typically less than 100, which translates to a flow that is completely laminar with no turbulence. Hence, under laminar flow, particles can be transported in a relatively predictable manner in the microfluidic channel. 71    Figure 3.14. A microfluidc flow cytometer based on impedometric detection. Reprinted (adapted) with permission from ref.13. Copyright (2005) American Chemical Society. The incorporation of microfluidic flow channel as the flow cell in the flow cytometer system depicted in Figure 3.14 creates a more sophisticated analytical system, which is fully capable of better particle sorting suspended in smaller sample volumes, thereby achieving shorter analysis time and cost-effectiveness. Being amenable to microfabrication techniques, the development of microfluidic flow cytometers based on a “lab-on-chip” concept becomes plausible. As a proof of concept, we demonstrated in Chapter that by incorporating graphene transistor array with microfluidic flow cytometric assay, we were able to distinguish electrically healthy red blood cells from malaria infected ones. The use of graphene as the electrical detector is apt owing to its electrical sensitivity and atomic thinness which will not interfere with the hydrodynamics in the microenvironment. This demonstration, concomitant with the successful distinction between red blood cells and white blood cells20 and implementation of commercially portable microfluidic flow cytometer for the screening of human immunodeficiency virus (HIV) bear 72    testament to the potential use of microfluidic flow cytometric assay in clinical applications. 3.6. 1. References Banwell, C. N.; McCash, E. M., Fundamentals of Molecular Spectroscopy. 4th ed.; McGraw-Hill: New Delhi, 1995. 2. Brisdon, A. K., Inorganic Spectroscopic Methods. Oxford University Press: Oxford; New York, 1998. 3. Casiraghi, C.; Hartschuh, A.; Qian, H.; Piscanec, S.; Georgi, C.; Fasoli, A.; Novoselov, K. S.; Basko, D. M.; Ferrari, A. C., Raman spectroscopy of graphene edges. Nano Lett 2009, 9, 1433-1441. 4. Ferrari, A. C.; Meyer, J. C.; Scardaci, V.; Casiraghi, C.; Lazzeri, M.; Mauri, F.; Piscanec, S.; Jiang, D.; Novoselov, K. S.; Roth, S.; Geim, A. K., Raman Spectrum of Graphene and Graphene Layers. Physical Review Letters 2006, 97, 187401. 5. Das, A.; Pisana, S.; Chakraborty, B.; Piscanec, S.; Saha, S. K.; Waghmare, U. V.; Novoselov, K. S.; Krishnamurthy, H. R.; Geim, A. K.; Ferrari, A. C.; Sood, A. K., Monitoring dopants by Raman scattering in an electrochemically topgated graphene transistor. Nature Nanotechnology 2008, 3, 210-215. 6. Graf, D.; Molitor, F.; Ensslin, K.; Stampfer, C.; Jungen, A.; Hierold, C.; Wirtz, L., Spatially resolved raman spectroscopy of single- and few-layer graphene. Nano Letters 2007, 7, 238-242. 73    7. Li, D.; Muller, M. B.; Gilje, S.; Kaner, R. B.; Wallace, G. G., Processable aqueous dispersions of graphene nanosheets. Nature Nanotechnology 2008, 3, 101-105. 8. Becerril, H. A.; Mao, J.; Liu, Z.; Stoltenberg, R. M.; Bao, Z.; Chen, Y., Evaluation of solution-processed reduced graphene oxide films as transparent conductors. ACS Nano 2008, 2, 463-470. 9. Somorjai, G. A., Introduction to Surface Chemistry and Catalysis. Wiley: New York, 1994. 10. Benda, A.; Benes, M.; Marecek, V.; Lhotsky, A.; Hermens, W. T.; Hof, M., How to determine diffusion coefficients in planar phospholipid systems by confocal fluorescence correlation spectroscopy. Langmuir 2003, 19, 4120-4126. 11. Krichevsky, O.; Bonnet, G., Fluorescence correlation spectroscopy: the technique and its applications Rep. Prog. Phys. 2002, 65, 251-297. 12. Lenne, P.-F.; Rigneault, H.; Marguet, D.; Wenger, J., Fluorescence fluctuations analysis in nanoapertures: physical concepts and biological applications. Histochemistry and Cell Biology 2008, 130, 795-805. 13. Macháň, R.; Hof, M., Recent Developments in Fluorescence Correlation Spectroscopy for Diffusion Measurements in Planar Lipid Membranes. Int. J. Mol. Sci. 2010, 11, 427-457. 14. Bruna, M.; Borini, S., Optical constants of graphene layers in the visible range. Applied Physics Letters 2009, 94, 031901-031903. 15. Nomarski, G., Microinterféromètre différentiel ondes polarisées. J. Phys. Radium 1955, 16, 9S-11S. 74    16. Kyser, D. F.; Viswanathan, N. S., Monte Carlo simulation of spatially distributed beams in electron-beam lithography. Journal of Vacuum Science and Technology 1975, 12, 1305-1308. 17. Rai-Choudhury, P., Handbook of Microlithography, Micromachining and Microfabrication SPIE Optical Engineering Press Bellingham, Washington, USA, 1997; Vol. 1. 18. Chung, T. D.; Kim, H. C., Recent advances in miniaturized microfluidic flow cytometry for clinical use. Electrophoresis 2007, 28, 4511-4520. 19. Wolff, A.; Perch-Nielsen, I. R.; Larsen, U. D.; Friis, P.; Goranovic, G.; Poulsen, C. R.; Kutter, J. P.; Telleman, P., Integrating advanced functionality in a microfabricated high-throughput fluorescent-activated cell sorter. Lab on a Chip 2003, 3, 22-27. 20. Chun; Chung, T. D.; Kim, H. C., Cytometry and Velocimetry on a Microfluidic Chip Using Polyelectrolytic Salt Bridges. Analytical Chemistry 2005, 77, 2490-2495. 21. D'Archangelo, M., Flow cytometry: new guidelines to support its clinical application. Cytometry B Clin Cytom 2007, 72, 209-210. 75    [...]... 10 6 5.2.4 Raman and optical contrast spectroscopy 10 7 5.3 Results and discussion 10 7 5.3 .1 Characterisation of big sized GO (BSGO) sheets 10 7 5.3.2 Characterisation of graphene thin film FET 11 0 5.3.3 Fabrication and characterisation of all-carbon FET 11 4 5.3.4 Factors influencing carrier mobility 11 5 5.3.4 .1 Graphene/ metal and graphene/ graphene interface 11 5 5.3.4.2... protein-functionalised graphene in solution (blue curve based on experimental data in Figure 7.6 for protein-functionalised graphene) and under influence of charge impurity density with input parameters for black curve (ε = 1, z = 1 nm, Nic = 1. 75 10 12/cm2), red curve ( ε = 1, z = 2 nm, Nic = 3.5 10 12/cm2), yellow curve (ε = 10 , z = 1 nm, Nic = 5 10 12/cm2) and green curve (ε = 10 , z = 2 nm, Nic = 8 10 12/cm2)... all-carbon transistor performance 11 7 5.4 Conclusion 12 0 5.5 References 12 1 IX    PART III GRAPHENE BIOHYBRID DEVICES Chapter 6: A Bioelectronic Platform Using Graphene- Lipid Bilayer Interface 6 .1 Introduction 12 4 6.2 Materials and methods 12 5 6.2 .1 Fabrication of CVD graphene film 12 5 6.2.2 Fabrication and measurement of CVD GFET 12 6 6.2.3 Formation... fullerene, one-dimensional (1D) carbon nanotube (CNT) or three-dimensional (3D) graphite 1   1. 2 .1 Unique structure and properties of graphene Single-layer graphene has two atoms per unit cell denoted as A and B in Figure 1. 1,3 giving rise to two conical points (minima), K and K’, in its 2D Brillouin zone, where band crossing between the conduction and valence bands occurs As such, graphene can be perceived... preparation 15 9 7.2.5 Optimisation of microfluidic flow cytometric assay 15 9 7.2.6 DIC microscopy and video analysis 16 0 7.2.7 AFM tip functionalisation and force curves analysis 16 0 7.3 Results and discussion 16 1 7.3 .1 Biosensing mechanism for single malaria infected cell by GFET 16 1 7.3.2 Characterisation of CD36-functionalised graphene 16 3 7.3.3 Simultaneous optical and electrical... quality graphene sheets and (2) the fundamental understanding of the interface between biological entities and graphene The work involved in this dissertation therefore relates to these two points and is broadly divided into two sections, namely the chemical routes to exfoliated graphene sheets and the fabrication of graphene biohybrid devices for protein and cellular sensing Several key factors that... Figures Figure 1. 1 (Left) Honeycomb lattice of single-layer graphene showing C atoms in A and B sublattices (Right) Band dispersion of graphene showing the π bands touching one another at the K point, and the Dirac cone approximation to E(k) relation for small k around Dirac point (K) Reproduced with permission from ref.3 Copyright (2 010 ) IEEE Figure 1. 2 (a) Structural model and (b) 3D view of graphene showing... trophozoite-PE and schizont-PE velocity obtained from the time taken for PE to cross graphene channel of 15 µm The top and bottom of the box denote 75th and 25th percentiles of the population respectively, while the top and bottom whiskers denote 90th and 10 th percentiles respectively Maximum and minimum values are denoted by open squares Gaussian distribution of raw data points is shown Figure 7 .10 Effect... as a semiconductor with vanishing bandgap Figure 1. 1 (Left) Honeycomb lattice of single-layer graphene showing C atoms in A and B sublattices (Right) Band dispersion of graphene showing the π bands touching one another at the K point, and the Dirac cone approximation to E(k) relation for small k around Dirac point (K) Reproduced with permission from ref.3 Copyright (2 010 ) IEEE Since graphene is made... images on the right Device channel length and width was 8 µm and 15 µm, respectively (b) Box plots of percentage conductance XXIII    changes for trophozoite-PE and schizont-PE The top and bottom of the box denote 75th and 25th percentiles of the population respectively, while the top and bottom whiskers denote 90th and 10 th percentiles respectively Maximum and minimum values are denoted by open squares . graphene 2 1. 2.2. Synthesis routes to graphene 5 1. 3. Graphene as a transducer in field-effect transistor (FET) sensor 11 1. 4. Overview of objectives and work scope 13 1. 5. References 15 Chapter. Abbreviations and Symbols XXV PART I BASIC ASPECTS Chapter 1: Introduction 1. 1. An introduction to carbon materials 1 1. 2. Background on graphene 1 1. 2 .1. Unique structure and properties of graphene.   CHEMICAL GROWTH ROUTES TO GRAPHENE AND GRAPHENE APPLICATIONS ANG KAILIAN PRISCILLA NATIONAL UNIVERSITY OF SINGAPORE 2 012   CHEMICAL GROWTH ROUTES TO