Growth and Characterization of Germanium and Silicon Nanostructures Huang Jinquan A Thesis Submitted for the Degree of Doctor of Philosophy Department of Electrical and Computer Engineering National University of Singapore 2010 i Abstract In this dissertation, the growth and characterization of five different types of germanium (Ge) and silicon (Si) nanostructures are presented The nanostructures include one-dimensional Ge nanowires (GeNWs), GeSi oxide nanotubes (GeSiOxNTs), heterostructures of GeNW-GeSiOxNT, Si nanowires (SiNWs) and near zerodimensional Ge nanodots (GeNDs) The first three were obtained using bottom-up approaches where the materials were self-assembled together with the aid of metal catalysts The formation of the SiNWs, on the other hand, was by a top-down process making use of metal nanodots formed using an anodized aluminium oxide (AAO) template AAO was also utilized as a thermal evaporation mask for the deposition of the regular arrays of GeNDs The formation mechanism of each type of nanostructure was investigated in detail GeNWs were obtained via the vapour-liquid-solid growth catalyzed by active gold (Au) droplets On the other hand, the formation of the GeSiOxNTs required passivation of the Au catalyst so that growth was limited to the rims of the Au dots Consequently, the GeNW-GeSiOxNT heterostructure was a result of timely control of the Au passivation such that formations of hollow tubes and solid wires took place at different time For the top-down fabrication of SiNWs, uniform and well-aligned SiNWs were produced by chemical wet etching using AAO-templated chromium/gold nanodots as a hard mask blocking material This dissertation also explored some unique properties of the as-synthesized nanostructures In particular, thermal conductance measurements have shown that the wire-tube heterostructure demonstrated a thermal rectification as high as 6% The different charge-trapping characteristics of the GeNDs were also studied using the scanning capacitance microscopy technique ii Acknowledgements First and foremost, I am particularly grateful to my thesis supervisors: Wai Kin for his support and guidance, especially his enigmatic encouragement in looking out for serendipity which indeed miraculously happened; Shijie for allowing me extreme freedom in pursuing any area of my interest in my Ph.D studies I am also extremely fortunate to have worked with Sing Yang, my “master” in all areas including the correct approach to research, the intelligent tricks, e.g how to be at least not-wrong when I cannot prove I am right, in manuscript preparation, the happy hours in WalaWala, my first Kilkenny beer (and the countless ones after), etc Special thanks also go out to: Nancy for the numerous TEM sessions she performed for me and I sincerely wish that her eyesight did not suffer as a result; Prof John Thong for his gracious accommodation in CICFAR, and Mrs Ho and Chee Keong for their help in preventing a logistical nightmare Their hearts must still be fluttering with fear after my two unintentional, and fortunately unsuccessful, attempts to “destroy” the lab using fire and flood Meng Lei and Chee Leong for the regular tea sessions during my thesis writing days though they seldom helped to wash the tea sets Rongguo and Cong-Tinh for the thermal rectification measurements Folks like Anna, Pi Can, Ren Yi, Wang Rui, Huijuan, Ziqian, Alfred, Heng Wah, Shi Fa, Jason and many others for their wonderful company; some must have profited a lot over the bets and the mahjong games that I lost during my stay in CICFAR Lastly, I am eternally grateful to my family My sisters and my brother for taking care of my mum, who has always treated me with unconditional love and care My dad, who now must have been blessing me in the other world His strict home teachings had trained me well and helped me tide over the difficult time in my Ph.D studies Table of Contents iii Table of Contents Abstract i Acknowledgements ii Table of Contents iii List of Figures vii List of Tables xiii Chapter Introduction and Motivation 1.1 Nanotechnology 1.2 Semiconductor Nanostructures 1.3 Challenges and Opportunities in Syntheses of Si and Ge Nanostructures 1.4 Organization of Thesis Chapter 2.1 Literature Review VLS Growth of Si and Ge Nanowires 2.1.1 VLS Mechanism and Its Variants 2.1.2 Factors affecting VLS Growth 12 2.2 SiNWs through Catalytic Etching 22 2.2.1 One-step Etching in Ionic Metal HF Solutions 23 2.2.2 Etching in HF/H2O2 with Patterned Metal Catalyst 29 2.3 VLS and Catalytic Etching as Complementary Methods 30 2.3.1 Material Types 30 2.3.2 Axial Orientation 31 Table of Contents iv 2.3.3 Nanowire Morphology 34 Summary 36 Chapter 3.1 Theory 37 Anodic Aluminium Oxide 37 3.1.1 Anodization Process 38 3.1.2 Mechanism for Formation of Regular Hexagonal Pore Arrays 39 3.1.3 Anodization of Al with Pre-textured Surface 44 3.1.4 Ultra-Thin AAO as an Evaporation Mask 47 3.2 Scanning Capacitance Microscopy (SCM) 49 3.2.1 SCM Operation Principle 50 3.2.2 SCM Operation Modes 56 Summary 62 Chapter GeNWs and GeSiOxNTs 63 4.1 Introduction 63 4.2 Experiment and Results 64 4.2.1 Sample preparation 64 4.2.2 GeNWs 66 4.2.3 GeSiOxNTs 69 4.3 Growth Mechanism 76 Summary 82 Chapter Heterostructures of GeNW and GeSiOxNT 83 5.1 Introduction 83 5.2 Experimental Details 85 Table of Contents v 5.3 Results and Analysis 86 5.3.1 Structural Characterization 86 5.3.2 Chemical Composition 90 5.4 Growth Mechanism 93 5.5 Application in Thermal Rectification 98 Summary 104 Chapter Well-aligned and Uniform SiNWs by Catalytic Etching 105 6.1 Introduction 105 6.2 Experimental Setup and Procedures 108 6.2.1 Control Experiment 108 6.2.2 Fabrication Procedure 110 6.3 Results and Discussion 112 6.3.1 General Morphology 112 6.3.2 Crystallinity 116 6.3.3 Precise Diameter Control 117 6.3.4 Other Masking Metals 121 Summary 127 Chapter GeNDs and Their Charge Trapping Characteristics 129 7.1 Introduction 129 7.2 GeND Fabrication 130 7.3 Results and Discussion 131 7.3.1 Surface Morphology of GeNDs 131 7.3.2 SCM Characterization 133 7.3.3 Group II GeNDs 142 Table of Contents vi Summary 144 Chapter Conclusion 145 8.1 Summary of Findings and Conclusion 145 8.2 Future Works 148 References 149 Appendix A: List of Publications 170 A1 Thesis-related Publications 170 A2 Other Publications 170 List of Figures vii List of Figures Figure 1-1 Intel central processing unit (CPU) transistor count trend Figure 2-1 (a) Au-Si binary phase diagram showing the compositional and phase evolution during the nanowire VLS growth process (b) Schematic depiction of the nanowire VLS growth Figure 2-2 Plot of the optimum growth temperature as a function of the diameter of the gold particle seeds for CVD growth of GeNWs 16 Figure 2-3 Variation in the shapes of GeNWs at different temperatures 20 Figure 2-4 Variation in the diameter and the aspect ratio of the GeNWs as (a) a function of pressure of GeH4 at 290 °C, and (b) a function of the growth temperature at 40 Torr of GeH4 21 Figure 2-5 (a) Scanning electron microscopy (SEM) micrographs of large-area SiNWs obtained in this project by catalytic etching in HF/AgNO3 (b) SEM image of the SiNWs at a higher magnification 24 Figure 2-6 Schematic depiction of the formation of vertically aligned SiNWs on a Si surface in ionic AgNO3/HF solution 27 Figure 2-7 HRTEM images of (a) an alloy-wire interface of a SiNW with a growth axis, (b) an alloy-wire interface of SiNW with a growth axis, (c) HRTEM cross-sectional image, and (d) the equilibrium shape for the wire cross sections predicted by Wulff construction 32 Figure 2-8 SEM micrographs of regular arrays of (a) Si nanowires of oval crosssections, (b) Si nanofins and (c) cylindrical nanowires obtained through laser interference lithography with different conditions combined with catalytic etching 35 Figure 3-1 Scanning electron microscopy (SEM) micrographs taken at (a) a 0o-tilt view and (b) a 45o-tilt view of an AAO template (with barrier layer removed) used in this project (c) SEM images of regular metal nanodots and (d) carbon nanotubes synthesized through the use of AAO templates 38 Figure 3-2 Simplified schematic of an electrolytic cell for aluminium anodization 39 Figure 3-3 Schematic diagrams for the electric-field strength distribution in some typical oxide barrier layers with the electrolyte-oxide interface marked by A, B, C and the oxide-metal interface marked by A’, B’, C’ 41 List of Figures viii Figure 3-4 (a) Two neighbouring pores having a separation larger than 2dE (b) The pores move towards each other to achieve a wall thickness of 2dE (c) The pores move closer with 2dW < 2dE (not drawn to scale) and a balanced curvature of 2θ < 180o (d) Two neighbouring pores that are too close to each other and (e) their self-adjustment to increase the wall thickness 42 Figure 3-5 SEM micrographs of (a) a barrier layer with hexagonally packed structure, viewed at a 0o-tilt, and (b) an oblique angle view of the cross-section of a typical AAO used in this project 43 Figure 3-6 SEM micrographs of AAO templates obtained from different acid electrolytes 44 Figure 3-7 Schematic depiction of formation of self-ordered porous AAO through a two-step anodization 46 Figure 3-8 Effect of surface pretexturing on anodization 47 Figure 3-9 SEM micrographs of ordered AAOs with inter-pore distances of (a) 100 nm, (b) 150 nm, and (c) 200 nm 47 Figure 3-10 Procedures of formation of metal dot arrays by evaporation through an AAO template 48 Figure 3-11 (a) Typical setup for atomic force microscopy (AFM) (b) Force-distance diagram showing the different regimes of tip deflection 51 Figure 3-12 Basic SCM detection system 53 Figure 3-13 The capacitance measured by the SCM sensor varies as the carriers move towards and away from the conductive cantilever tip 54 Figure 3-14 (a) High-frequency CV curves for a heavily and a lowly doped n-type semiconductor The CV curves in (b) shows the δC/δV for both n- and p-type materials 55 Figure 3-15 (a) 2D Topography image by AFM of the SRAM test sample used in this project, and (b) its reconstruction in 3D 56 Figure 3-16 SCM contrast images of the SRAM sample taken in (a) amplitude mode, and (b) hybrid-data mode with a 90o lock-in phase 58 Figure 3-17 Section analysis along the white line indicated in Figure 3-16(b) 58 Figure 3-18 High frequency CV curves and the corresponding differential capacitance δC/δV dependence on the dc bias for (a) n-type, and (b) p-type semiconductors 60 List of Figures ix Figure 3-19 Effect of different charges on (a) the high frequency CV curve, and (b) the δC/δV curve 61 Figure 4-1 Block diagram of a thermal evaporation system 65 Figure 4-2 (a) SEM micrograph of individual Au-dots obtained by annealing a nm Au film (b) Size distribution of 100 typical Au-dots randomly selected across the sample 66 Figure 4-3 (a) Setup, and (b) temperature setting for GeNW growth 67 Figure 4-4 (a) and (b) SEM images showing GeNWs with smooth surface morphology (c) TEM image of several Ge nanowires, which have a uniform diameter of about 80 nm.(d) High resolution TEM (HRTEM) image of a single Ge nanowire showing the growth direction and its SAED image (inset) 69 Figure 4-5 Block diagram of the experimental setup for the growth of GeSiOxNTs 70 Figure 4-6 (a) SEM image of the as-synthesized GeSiOxNTs (b) Close examination of the nanotubes reveals that each nanotube is a long, tubular structure with uniform diameter (c) and (d) SEM images showing the open-ended GeSiOxNTs and the wavy surface of the walls of the tubular structure 71 Figure 4-7 (a) TEM image of a single GeSiOxNT and (b) its HRTEM image 72 Figure 4-8 (a) Ge3d core level XPS spectra and (b) Si2p XPS spectra of GeSiOxNTs 74 Figure 4-9 STEM-EDX mapping of (b) Ge, (c) O and (d) Si of a typical GeSiOxNT in (a) 74 Figure 4-10 TEM spot EDX spectrum of a typical GeSiOxNT 75 Figure 4-11 (a) to (c): TEM images of a single GeSiOxNT showing gradual shape transformation under electron beam bombardment in the TEM (d) TEM images of a GeSiOxNT of 80 nm in diameter collapsing into (e) a solid nanowire of 50 nm in diameter 76 Figure 4-12 Schematic depiction of the growth mechanism of the GeSiOxNTs 80 Figure 4-13 (a) SEM image showing the Au dots on the surface of a growth sample with nanotubes removed (b) SEM-EDX on the Au dots in (a) reveals little Ge incorporation into the Au catalyst dots 81 Figure 5-1 Temperature profiles of Ge and GeI4 sources and Au-dotted Si substrate for the growth of (a) GeSiOxNT homostructures and (b) GeNW-GeSiOxNT heterostructures 85 References 157 84 Fang, H.; Wu, Y.; Zhao, J.; Zhu, J., “Silver catalysis in the fabrication of silicon nanowire arrays”, Nanotechnology, vol 17, p 3768 (2006) 85 Peng, K.; Hu, J.; Yan, Y.; Wu, Y.; Fang, H.; Xu, Y.; Lee, S T.; Zhu, J., “Fabrication of single-crystalline silicon nanowires by scratching a silicon surface with catalytic metal particles”, Adv Funct Mater., vol 16, p 387 (2006) 86 Peng, K.; Zhang, M L.; Lu, A J.; Wong, N B.; Zhang, R Q.; Lee, S T., “Ordered silicon nanowire arrays via nanosphere lithography and metal-induced etching”, Appl Phys Lett., vol 90, p 163123 (2007) 87 Huang, Z.; Fang, H.; Zhu, J., “Fabrication of silicon nanowire arrays with controlled diameter, length and density”, Adv Mater., vol 16, p 744 (2007) 88 Choi, W K.; Liew, T H.; Dawood, M K.; Smith, H I.; Thompson, C V.; Hong, M H., “Synthesis of silicon nanowires and nanofin arrays using interference lithography and catalytic etching”, Nano Lett., vol 8, p 3799 (2008) 89 Huang, Z.; Zhang, X.; Reiche, M.; Liu, L.; Lee, W.; Shimizu, T.; Senz, S.; Gösele, U., “Extended arrays of vertically aligned sub-10nm diameter [100] Si nanowires by metal-assisted chemical etching”, Nano Lett., vol 8, p 3046 (2008) 90 Huang, Z.; Shimizu, T.; Senz, S.; Zhang, Z.; Zhang, X.; Lee, W.; Geyer, N.; Gösele, U., “Ordered arrays of vertically aligned [110] silicon nanowires by suppressing the crystallographically preferred etching directions”, Nano Lett., vol 9, p 2519 (2009) 91 Fang, C.; Foll, H.; Cartensen, J., “Long germanium nanowires prepared by electrochemical etcing”, Nano Lett., vol 6, p 1578 (2006) 92 Wang, X.; Pey, K L.; Choi, W K.; Ho, C K F.; Fitzgerald, E.; Antoniadis, D., “Arrayed Si/SiGe nanowire and heterostructure formations via Au-assisted wet chemical etching method”, Electrochem Solid St., vol 12, p K37 (2009) 93 Geyer, N.; Huang, Z.; Fuhrmann, B.; Grimm, S.; Reiche, M.; Nguyen-Duc, T K.; Borr, J.; Leipner, H S.; Werner, P.; Gösele, U., “Sub-20 nm Si/Ge superlattice nanowires by metal-assisted etching”, Nano Lett., vol 9, p 3106 (2009) References 158 94 Lu, W.; Lieber, C M., “Semiconductor nanowires”, J Phys D: Appl Phys., vol 39, p R387 (2006) 95 Hisamoto, D.; Lee, W C.; Kedzierski, J.; Takeuchi, H.; Asano, K.; Kuo, C.; Anderson, E.; King, T J.; Bokor, J.; Hu, C M., “FinFET- A self-aligned doublegate MOSFET scalable than 20nm”, IEEE Trans Electron Devices, vol 47 p 2320 (2000) 96 Kedzierski, J.; Ieong, M.; Nowak, E.; Kanarsky, T S.; Zhang, Y.; Roy, R.; Boyd, D.; Fried, D.; Wong, H S P., “Extension and source/drain design for highperformance FinFET devices”, IEEE Trans Electron Devices, vol 50 p 952 (2003) 97 Cheng, G.; Kolmakov, A.; Zhang, Y.; Moskovits, M; Munden, R.; Reed, M A.; Zhang, J., “Current rectification in a single GaN nanowire with a well-defined p-n junction”, Appl Phys Lett., vol 83, p 1578 (2003) 98 Martin, C R., “Nanomaterials: a membrane-based synthetic approach”, Science, vol 266, p.1961 (1994) 99 Masuda, H.; Fukuda, K., “Ordered metal nanohole arrays made by a two-step replication of honeycomb structures of anodic alumina”, Science, vol 268, pp.1466 (1995) 100 Nielsch, K.; Muller, F.; Li, A P.; Gösele, U., “Uniform nickel deposition into ordered alumina pores by pulsed electrodeposition”, Adv Mater., vol 12, p 582 (2000) 101 Hoyer, P., “Formation of a titanium dioxide nanotube array”, Langmuir, vol 12, p 1411 (1996) 102 Li, J.; Papadopoulos, C.; Xu, J M.; Moskovits M., “Highly-ordered carbon nanotube arrays for electronics applications”, Appl Phys Lett., vol.75, p 367 (1999) 103 Su, Z.; Buhl, M.; Zhou, W., “Dissociation of water during formation of anodic aluminium oxide”, J Am, Chem Soc., vol 131, p 8697 (2009) References 159 104 Su, Z.; Zhou, W., “Formation mechanism of porous anodic aluminium and titanium oxides”, Adv Mater., vol 20, p 3663 (2008) 105 Cherki, C.; Siejka, J., “Study by nuclear microanalysis and 018 tracer techniques of the oxygen transport processes and the growth laws for porous anodic oxide layers on aluminium”, J Electrochem Soc., vol 120, p 784 (1973) 106 Siejka, J.; Ortega, C., “An O18 study of field-assisted pore formation in compact anodic oxide films on aluminium”, J Electrochem Soc., vol 124, p 883 (1977) 107 Jessensky, O.; Muller, F.; Gösele, U., “Self-organized formation of hexagonal pore arrays in anodic alumina”, Appl Phys Lett., vol 72 p 1173 (1998) 108 Diggle, J W.; Downie, T C.; Goulding, C W., “Anodic oxide films on aluminium’, Chem Rev., vol 69, p 365 (1969) 109 Masuda, H.; Satoh, M., “Fabrication of gold nanodot array using anodic porous alumina as an evaporation mask”, Jpn J Appl Phys., vol 35, p L126 (1996) 110 Masuda, H.; Yamada, H.; Satoh, M.; Asoh, H.; Nakao, M.; Tamamura, T., “Highly ordered nanochannel-array architecture in anodic alumiuna”, Appl Phys Lett., vol 71, p 2770 (1997) 111 O'Sullivan, J P.; Wood, G C., “The morphology and mechanism of formation of porous anodic films on aluminium”, Proc R Soc London, Ser A, vol 317, p 511, (1970) 112 Williams, C C., “Two-dimensional dopant profiling by scanning capacitance miscroscopy”, Annu Rev Mater Res., vol 29, p 471 (1999) 113 Naitou, Y.; Ando, A.; Ogiso, H.; Kamiyama, S.; Nara, Y.; Nakamura, K.; Watanabe, H.; Yasutake, K., “Spatial fluctuation of dielectric properties in Hfbased high-k gate films studied by scanning capacitance microscopy”, Appl Phys Lett., vol 87, p 252908 (2005) 114 Binnig, G.; Quate, C F., “Atomic force microscope”, Phys Rev Lett., vol 56, p 930 (1986) References 160 115 Cappella, B.; Baschieri, P.; Frediani, C.; MIccoli, P.; Ascoli, C., “Force- distance curves by AFM”, IEEE Eng Med Boil., vol 16, p 58 (1997) 116 Roiter, Y.; Minko, S., “AFM single molecule experiments at the solid-liquid interface: in situ conformation of adsorbed flexible polyelectrolyte chains”, J Am Chem Soc., vol 127, p 15688 (2005) 117 Digital Instruments Metrology Group (Veeco), Scanning Capacitance Microscopy Support Note, no 224, Rev D (1999) 118 Nakakura, C Y.; Hetherington, D L.; Shaneyfelt, M R.; Shea, P J., "Observation of metal-oxide-semiconductor transistor operation using scanning capacitance microscopy", Appl Phys Lett., vol 75, p 2319 (1999) 119 Edwards, H.; Ukraintsev, V A.; Martin, R S.; Johnson, F S.; Menz, P.; Walsh, S.; Ashburn, S.; Wills, K S.; Harvey, K.; Chang, M C., “P-N junction delineation in Si devices using scanning capacitance spectroscopy”, J Appl Phys., vol 87, p 1485 (2000) 120 Chuang, T C.; Shen, C M.; Lin, S C.; Huang, C M.; Chou, J H.; Lee, J C., “Alternating plane-view and cross-section scanning capacitance microscope technique to reveal various implant issue”, Conference Proceedings from the 33rd International Symposium for Testing and Failure Analysis (ISTFA), p 52 (2007) 121 Chim, W K.; Wong, K M.; Yeow, Y T.; Hong, Y D.; Lei, Y.; Teo, L W.; Choi, W K., “Monitoring oxide quality using the spread of the δC/δV peak in scanning capacitance microscopy measurements”, IEEE Electr Device L., vol 24, p 667, (2003) 122 Wong, K M.; Chim, W K.; Yan, J., “Physical mechanism of oxide interfacial traps, carrier mobility degradation and series resistance on contrast reversal in scanning-capacitance-microscopy dopant concentration extraction”, Appl Phys Lett., vol 87, p 053504 (2005) 123 Chim, W K.; Wong, K M.; Teo, Y L.; Lei, Y.; Yeow, Y T., “Dopant extraction from scanning capacitance microscopy measurements of p-n junctions References 161 using combined inverse modeling and forward simulation”, Appl Phys Lett., vol 80, p 4837 (2002) 124 Wong, K M.; Chim, W K., Ang, K W.; Yeo, Y C., “Spatial distribution of interface trap density in strained channel transistors using the spread of the differential capacitance characteristics in scanning capacitance microscopy measurements”, Appl Phys Lett., vol 90, p 153507 (2007) 125 Wong, K M.; Chim, W K., “Theoretical model of interface trap density using the spread of the differential capacitance characteristics in scanning capacitance microscopy measurements”, Appl Phys Lett., vol 88, p 083510 (2006) 126 Lide, D R (ed.), “Section 12, Properties of solids: Properties of semiconductors”, CRC Handbook of Chemistry and Physics, 90th Edition, CRC Press (2009) 127 Sze, S M., Physics of Semiconductor Devices, 2nd ed., Wiley, New York (1981) 128 Maeda, Y.; Tsukamoto, N.; Yazawa, Y.; Kanemitsu, Y.; Masumoto, Y., “Visible photoluminescence of Ge microcrystals embedded in SOS glassy matrices”, Appl Phys Lett., vol 59, p 3168 (1991) 129 Kamins, T I.; Li, X.; Williams, R S., “Growth and structure of chemically vapour deposited Ge nanowires on Si substrates”, Nano Lett., vol 4, p 503 (2004) 130 Jagannathan, H.; Deal, M.; Nishi, Y.; Woodruff, J.; Chidsey, C.; Mclntyre, P C., “Nature of germanium nanowire heteroepitaxy on silicon substrates”, J Appl Phys., vol 100, p 024318 (2006) 131 Nguyen, P.; Ng, H T.; Meyyappan, M., “Growth of individual vertical germanium nanowires”, Adv Mater., vol 17, p 549 (2005) 132 Sun, X H.; Didychuk, C.; Sham, T K.; Wong, N B., “Germanium nanowires: synthesis, morphology and local structure studies”, Nanotechnology, vol 17, p 2925 (2006) References 162 133 Mei, Y F.; Siu, G G.; Li, Z M.; Fu, R K Y.; Tang, Z K.; Chu, P K., “Polycrystalline tubular nanostructures of germanium”, J Cryst Growth, vol 285, p 59 (2005) 134 Han, W Q.; Wu, L.; Zhu, Y.; Strongin, M., “In-situ formation of ultrathin Ge nanobelts bonded with nanotubes”, Nano Lett., vol 5, p 1419 (2005) 135 Vapour pressure of Ge: x 10-7 Torr at 900 oC and x 10-7 Torr at 939 oC (melting point) Retrived on April 21, 2010 from Veeco website: http://www.veeco.com/library/Learning_Center/Growth_Information/Vapor_Press ure_Data_For_Selected_Elements/index.aspx 136 Li, C.; Liu, Z.; Gu, C.; Xu, X.; Yang, Y., “Controllable synthesis and growth model of amorphous silicon nanotubes with periodically dome-shaped interiors”, Adv Mater., vol 18, p 228 (2006) 137 Tuan, H Y.; Ghezelbash, A.; Korgel, B A., “Silicon nanowires and silica nanotubes seeded by copper nanoparticles in an organic solvent” Chem Mater., vol 20, p 2306 (2008) 138 Liang, C.; Terabe, K.; Hasegawa, T.; Aono, M., “Template synthesis of M/M2S (M=Ag, Cu) hetero-nanowires by electrochemical technique”, Solid State Ionics, vol 177, p 2527 (2006) 139 Sun, X.; Yu, B.; Meyyappan, M., “Synthesis and nanoscale thermal encoding of phase-change nanowires”, Appl Phys Lett., vol 90, p 183116 (2007) 140 Buffat, P.; Borel, J P., “Size effect on the melting temperature of gold particles”, Phys Rev A, vol 13, p 2287 (1976) 141 Wu, Y Y.; Yang, P D., “Melting and welding semiconductor nanowires in nanotubes”, Adv Mater., vol 13, p 520 (2001) 142 Goldberger, J.; Fan, R.; Yang, P D., “Inorganic nanotubes: a novel platform for nanofluidics”, Acc Chem Res., vol 39, p 239 (2006) 143 Lever, R F., “Gaseous equilibria in the germanium iodine system”, J Electrochem Soc., vol 110, p 775 (1963) References 163 144 Rolsten R F., Iodide Metals and Metal Iodides, John Wiley & Sons: New York, pp 300-304 (1961) 145 Wu, Y Y.; Yang, P D., “Germanium nanowire growth via simple vapour transport”, Chem Mater., vol 12, p 605 (2000) 146 Rodriguez, J F.; Mebrahtu, T.; Soriaga, M P., “Determination of the surface area of gold electrodes by iodine chemisorption”, J Electroanal Chem., vol 233, p 283 (1987) 147 Rodriguez, J F.; Soriaga, M P., “Reductive desorption of iodine chemisorbed on smooth polycrystalline gold electrodes”, J Electrochem Soc., vol 135, p 616 (1988) 148 Tadayyoni, M A.; Gao, P.; Weaver, M J., “Application of surface-enhanced raman spectroscopy to mechanistic electrochemistry - Oxidation of iodide at gold electrodes”, J Electroanal Chem., vol 198, p 125 (1986) 149 Wang, C Y.; Chan, L H.; Xiao, D Q.; Lin, T C.; Shih, H C., “Mechanism of solid-liquid-solid on the silicon oxide nanowire growth”, J Vac Sci Technol B, vol 24, p 613 (2006) 150 Yan, H F.; Xing, Y J.; Hang, Q L.; Yu, D P.; Wang, Y P.; Xu, J.; Xi, Z H.; Feng, S Q., “Growth of amorphous silicon nanowires via a solid-liquid-solid mechanism”, Chem Phys Lett., vol 323, p 224 (2000) 151 Hiraki, A.; Lugujjo, E.; Mayer, J W., “Formation of silicon dioxide over gold layers on silicon substrates”, J Appl Phys., vol 43, p 3643 (1972) 152 Kolasinski, K W., “Catalytic growth of nanowires: vapour-liquid-solid, vapour-solid-solid, solution-liquid-solid and solid-liquid-solid growth”, Curr Opin Solid St M., vol 10, p 182 (2006) 153 Cheng, W.; Dong, S.; Wang, E., “Iodine-induced gold-nanoparticle fusion/fragmentation/aggregation and iodine-linked nanostructured assemblies on a glass substrate”, Angew Chem Int Ed., vol 42, p 449 (2003) References 164 154 Wu, Y Y.; Fan, R.; Yang, P D., “Block-by-block growth of single-crystalline Si/SiGe superlattice nanowires”, Nano Lett., vol 2, p 83 (2002) 155 Minot, E D.; Kelkensberg, F.; Kouwen, M.; Dam, J A.; Kouwenhoven, L P.; Zwiller, V.; Borgstrom, M T.; Wunnicke, O.; Verheijen, M A.; Bakkers, E P A., “Single quantum dot nanowire LEDs”, Nano Lett., vol 7, p 367 (2007) 156 Clark, T E.; Nimmatoori, P.; Lew, K K.; Pan, L.; Redwing, J M.; Dickey, E C., “Diameter dependent growth rate and interfacial abruptness in vapour-liquidsolid Si/Si1-xGex heterostructure nanowires”, Nano Lett., vol 8, p 1246 (2008) 157 Lauhon, L J.; Gudiksen, M S.; Wang, D.; Lieber, C M., “Epitaxial core-shell and core-multishell nanowire heterostructures”, Nature, vol 420, p 57 (2002) 158 Wu, Y Y.; Yang, P D.; “Melting and welding semiconductor nanowires in nanotubes”, Adv Mater., vol 13, p 520 (2001) 159 Park, W I.; Yi, G C.; Kim, M.; Pennycook, S J., “Quantum confinement observed in ZnO/ZnMgO nanorod heterostructures”, Adv Mater., vol 15, p 526 (2003) 160 Goldberger, J.; He, R R.; Zhang, Y F.; Lee, S K.; Yan, H Q.; Choi, H J.; Yang, P D., “Single-crystal gallium nitride nanotubes”, Nature, vol 422, p 599 (2003) 161 Han, W Q.; Wu, L.; Zhu, Y.; Strongin, M., “In-situ formation of ultrathin Ge nanobelts bonded with nanotubes”, Nano Lett., vol 5, p 1419 (2005) 162 Xiang, R.; Luo, G.; Qian, W.; Zhang, Q.; Wang, Y.; Wei, F.; Li, Q.; Cao, A., “Encapsulation, compensation, and substitution of catalyst particles during continuous growth of carbon nanotubes”, Adv Mater., vol 19, p 2360 (2007) 163 Wu, H.; Wang, Q.; Yao, Y.; Qian, C.; Zhang, X.; Wei, X J., “Microwave- assisted synthesis and photocatalytic properties of carbon nanotube/zinc sulfide heterostructures”, Phys Chem C , vol 112, p 16779 (2008) References 165 164 Marsh, D H.; Rance, G A.; Whitby, R J.; Giustiniano, F.; Khlobystov, A N., “Assembly, structure and electrical conductance of carbon nanotube-gold nanoparticle 2D heterostructures”, J Mater Chem., vol 18, p 2249 (2008) 165 Yu, D.; Chen, Y.; Li, B.; Chen, X.; Zhang, M., “Fabrication and characterization of PbS/multiwalled carbon nanotube heterostructures”, Appl Phys Lett., vol 90, p 161103 (2007) 166 Li, F.; Cho, S H.; Son, D I.; Kim, T W.; Lee, S K.; Cho, Y H.; Jin, S., “UV photovoltaic cells based on conjugated ZnO quantum dot/multiwalled carbon nanotube heterostructures”, Appl Phys Lett., vol 94, p 111906 (2009) 167 Shen, G.; Chen, D.; Zhou, C., “One-step thermo-chemical synthetic method for nanoscale one-dimensional heterostructures”, Chem Mater., vol 20, p 3788 (2008) 168 Lao, J Y.; Wen, J G.; Ren, Z F., “Hierarchical ZnO nanostructures”, Nano Lett., vol 2, p 1287 (2002) 169 Gautam, U K.; Fang, X.; Bando, Y.; Zhan, J.; Golberg, D., “Synthesis, structure, and multiply enhanced field-emission properties of branched ZnS nanotube in nanowire coreshell heterostructures”, ACS Nano, vol 2, p 1015 (2008) 170 Mokari, T.; Banin, U., “Synthesis and properties of CdSe/ZnS core/shell nanorods”, Chem Mater., vol 15, p 3955 (2003) 171 Martin, B R.; Dermody, D J.; Reiss, B D.; Fang, M.; Lyon, L A.; Natan, M J.; Mallouk, T E., “Orthogonal self-assembly on colloidal gold-platinum nanorods”, Adv Mater., vol 11, p 1021 (1999) 172 Ostermann, R.; Li, D.; Yin, Y.; McCann, J T.; Xia, Y., “V2O5 nanorods on TiO2 nanofibers: A new class of hierarchical nanostructures enabled by electrospinning and calcination”, Nano Lett., vol 6, p 1297 (2006) 173 Zhang, R Q.; Lifshitz, Y.; Lee, S T., “Oxide-assisted growth of semiconducting nanowires”, Adv Mater., vol 15, p 635 (2003) References 166 174 Zhang, Y F.; Tang, Y H.; Wang, N.; Lee, C S.; Bello, I.; Lee, S T., “Germanium nanowires sheathed with an oxide layer”, Phys Rev B, vol 61, p 4518 (2000) 175 Hu, J Q.; Meng, X M.; Jiang, Y.; Lee, C S.; Lee, S T., “Fabrication of germanium-filled silica nanotubes and aligned silica nanofibres”, Adv Mater., vol 15, p 70 (2003) 176 Peng, H Y.; Pan, Z W.; Xu, L.; Fan, X H.; Wang, N.; Lee, C S.; Lee, S T., “Temperature dependence of silicon nanowire morphology” Adv Mater., vol 13, p 317 (2001) 177 Peng, H Y.; Wang, N.; Shi, W S.; Zhang, Y F.; Lee, C S.; Lee, S T., “Bulk- quantity Si nanosphere chains prepared from semi-infinite length Si nanowires”, J Appl Phys., vol 89, p 727 (2001) 178 Peierls, R E., Quantum Theory of Solids, Oxford Univ Press, London, (1955) 179 Lepri, S.; Livi, R.; Politi, A., “Thermal conduction in classical low-dimensional lattices”, Phys Rep., vol 377, p (2003) 180 Chang, C W.; Han, W Q.; Zettl, A., “Thermal conductivity of B-C-N and BN nanotubes”, J Vac Sci Technol B, vol 23, p 1883 (2005) 181 Hone, J.; Whitney, M.; Piskoti, C.; Zettl, A., “Thermal conductivity of single- walled carbon nanotubes”, Phys Rev B, vol 59, p R2514 (1999) 182 Chang, C W.; Okawa, D.; Majumdar, A.; Zettl, A., “Solid-state thermal rectifier”, Science, vol 314, p 1121 (2006) 183 Astakhova, T Y.; Gurin, O D.; Menon, M.; Vinogradov, G A., “Longitudinal solitons in carbon nanotubes”, Phys Rev B, vol 64, p 035418 (2001) 184 Savin, A V.; Savina, O I., “Nonlinear dynamics of carbon molecular lattices: Soliton plane waves in graphite layers and supersonic acoustic solitons in nanotubes”, Phys Solid State, vol 46, p 383 (2004) References 167 185 Iizuka, T.; Wadati, M., “Soliton transmission and reflection in discontinuous media”, J Phys Soc Jpn., vol 61, p 3077 (1992) 186 Sakai, S.; Samuelsen, M R.; Olsen, O H., “Perturbation analysis of a parametrically changed sine-Gordon equation”, Phys Rev B, vol 36, p 217 (1987) 187 Woafo, P., “Scattering of the φ4 kink with an interface”, Phys Rev E, vol 58, p 1033 (1998) 188 Goldberger, J.; Hochbaum, A I.; Fan, R.; Yang, P D., “Silicon vertically integrated nanowire field effect transistors”, Nano Lett., vol 6, p 973 (2006) 189 Zheng, G.; Lu, W.; Jun, S.; Lieber, C M., “Synthesis and fabrication of high- peformance n-type silicon nanowire transistors”, Adv Mater., vol 16, p 1890 (2004) 190 Ng, H T.; Han, J.; Yamada, T.; Nguyen, P.; Chen, Y P.; Meyyappan, M., “Single crystal nanowire vertical surround-gate field-effect transistor”, Nano Lett., vol 4, p 1247 (2004) 191 Li, Y.; Qian, F.; Xiang, J.; Lieber, C M., “Nanowire electronic and optoelectronic devices”, Mater Today, vol 9, p 18 (2006) 192 Kelzenberg, M D.; Turner-Evans, D B.; Kayes, B M.; Filler, M A.; Putnam, M C.; Lewis, N S.; Atwater, H A., “Photovoltaic measurements in singlenanowire silicon solar cells”, Nano Lett., vol 8, p 710 (2008) 193 Shimizu, T.; Senz, S.; Shingubara, S.; Gösele, U., “Synthesis of epitaxial Si(100) nanowires on Si(100) substrate using vapour-liquid-solid growth in anodic aluminium oxide nanopore arrays”, Appl Phys A: Mater Sci Process., vol 87, p 607 (2007) 194 Shimizu, T.; Xie, T.; Nishikawa, J.; Shingubara, S.; Senz, S.; Gösele, U., “Synthesis of rertical high-density epitaxial Si(100) nanowire arrays on a Si(100) substrate using an anodic aluminium oxide template”, Adv Mater., vol 19, p 917 (2007) References 168 195 Morton, K J.; Nieberg, G.; Bai, S.; Chou, S Y., “Wafer-scale patterning of sub-40 nm diameter and high aspect ratio (>50:1) silicon pillar arrays by nanoimprint and etching”, Nanotechnology, vol 19, p 345301 (2008) 196 Boor, J.; Geyer, N.; Wittemann, J V.; Gösele, U.; Schmidt, V., “Sub-100 nm silicon nanowires by laser interference lithography and metal-assisted etching”, Nanotechnology, vol 21, p 095302 (2010) 197 Solak, H H., “Nanolithography with coherent extreme ultraviolet light”, J Phys D: Appl Phys., vol 39, p R171 (2006) 198 Pevzner, A.; Engel, Y.; Elnathan, R.; Ducobni, T.; Ishai, M B.; Reddy, K.; Shpaisman, N.; Tsukernik, A.; Oksman, M.; Patolsky, F., “Knocking down highlyordered large-scale nanowire arrays” Nano Lett., vol 10, p 1202 (2010) 199 Choi, Y K.; Zhu, J.; Grunes, J.; Bokor, J.; Somorjai, G A., “Fabrication of sub-10-nm silicon nanowire arrays by size reduction lithography”, J Phys Chem B, vol 107, p 3340 (2003) 200 Williams, K R.; Gupta, K.; Wasilik, M., “Etch rates for micromachining processing - Part II”, J Microelectromech S., vol 12, p 761 (2003) 201 Lide, D R (ed.), “Section 9, Molecular structure and spectroscopy: Electronegativity”, CRC Handbook of Chemistry and Physics, 90th Edition, CRC Press (2009) 202 Li, X.; Bohn, P W., “Metal-assisted chemical etching in HF/H2O2 produces porous silicon”, Appl Phys Lett., vol 77, p 2572 (2000) 203 Borgstrom, M T.; Immink, G.; Ketelaars, B.; Algra, R.; Bakkers E P A M., “Synergetic nanowire growth”, Nat Nanotechnol., vol 2, p 541 (2007) 204 Chang, S W.; Chuang, V P.; Boles, S T.; Ross, C A.; Thompson, C V., “Densely packed arrays of ultra-high-aspect-ratio silicon nanowires fabricated using block-copolymer lithography and metal-assisted etching”, Adv Fuct Mater., vol 19, p 2495 (2009) References 169 205 Lee, W.; Ji, R.; Ross, C A.; Gösele, U.; Nielsch, K., “Wafer-scale Ni imprint stamps for porous alumina membranes based on interference lithography”, Small, vol 2, p 978 (2006) 206 Kustandi, T S.; Loh, W W.; Gao, H.; Low, H Y., “Wafer-scale near-perfect ordered porous alumina on substrates by step and flash imprint lithography”, ACS Nano, vol 4, p 2561 (2010) 207 Takeoka, S.; Fujii, M.; Hayashi, S.; Yamamoto, K., “Size-dependent near- infrared photoluminescence from Ge nanocrystals embedded in SiO2 matrices”, Phys Rev B, vol 58, p 7291 (1998) 208 Miesner, C.; Asperger, T.; Brunner, K.; Abstreiter, G., “Capacitance-voltage and admittance spectroscopy of self-assembled Ge islands in Si”, Appl Phys Lett., vol 77, p 2704 (2000) 209 Puntes, V F.; Krishnan, K M.; Alivisatos, A P.; “Colloidal nanocrystal shape and size control: The case of cobalt”, Science, vol 291, p 2115 (2001) 210 Pease, R F.; Han, L.; Winograd, G.; Meisburger, W D.; Pickard, D.; McCord, M A., “Prospects for charged particle lithography as a manufacturing technology”, Microelectron Eng., vol 53, p 55 (2000) 211 Erickson, A.; Sadwick, L.; Neubauer, G.; Kopanski, J.; Adderton, D.; Rogers, M., “Quantitative scanning capacitance microscope analysis of two-dimensional dopant concentrations at nanoscale dimensions”, J Electro Material, vol 25, p 301, (1996) 212 Kan, E W H.; Choi, W K.; Chim, W K.; Fitzgerald, E A.; Antoniadis, D A., “Origin of charge trapping in germanium nanocrystal embedded SiO2 system: Role of interfacial traps?” J Appl Phys., vol 95, p 3148 (2004) Appendix A: List of Publications 170 Appendix A: List of Publications A1 Thesis-related Publications Huang, J Q.; Chiam, S Y.; Tan, H H.; Wang, S J.; Chim, W K., “Synthesis of high-density and well-aligned silicon nanowires with precise diameter control using a metal nanodot array as a hard mask in chemical etching”, Chemistry of Materials, vol 22, pp 4111-4116, 2010 Huang, J Q.; Chiam, S Y.; Chim, W K.; Wong, L M.; Wang, S J., “Heterostructures of germanium nanowires and germanium-silicon oxide nanotubes and growth mechanisms”, Nanotechnology, vol 20, no 42, article no 425604, pp 425604-1 to 425604-8, 2009 Huang, J Q.; Chim, W K.; Wang, S J.; Chiam, S Y.; Wong, L M., “From germanium nanowires to germanium-silicon oxide nanotubes: Influence of germanium tetraiodide precursor”, Nano Letters, vol 9, no 2, pp 583-589, 2009 Huang, J Q.; Chim, W K.; Wang, S J.; Chiam, S Y.; Wong, L M., “Germanium nanostructures: Under control”, Nature Publishing Group, Asia Materials research highlight, 15 April 2009 Wong, K M.; Chim, W K.; Huang, J Q.; Zhu, L., “Scanning capacitance microscopy detection of charge trapping in free-standing germanium nanodots and the passivation of hole trap sites”, Journal of Applied Physics, vol 103, no 5, article no 054505, pp 054505-1 to 054505-5, 2008 A2 Other Publications Ren, Y.; Chim, W K.; Chiam, S Y.; Huang, J Q.; Pi, C.; Pan, J S., “Formation of nickel oxide nanotubes with uniform wall thickness by low-temperature thermal oxidation through understanding the limiting effect of vacancy diffusion and the Appendix A: List of Publications 171 Kirkendall phenomenon”, Advanced Functional Materials, vol 20, pp 3336-3342, 2010 Wong, L M.; Chiam, S Y.; Huang, J Q.; Wang, S J.; Pan, J S.; Chim, W K., “Energy band alignment of Cu2O and ZnO thin film heterojunctions”, Accepted for publication in Journal of Applied Physics, vol 108, no 3, article no 033702, pp 033702-1 to 033702-6, 2010 ... exploration of self-assembled synthesis and the possible applications of new Si and/ or Ge nanostructures and, (b) achieving a controlled growth of Si and Ge nanostructures 1.4 Organization of Thesis... Abstract In this dissertation, the growth and characterization of five different types of germanium (Ge) and silicon (Si) nanostructures are presented The nanostructures include one-dimensional... Temperature profiles of Ge and GeI4 sources and Au-dotted Si substrate for the growth of the wire-tube heterostructures 93 Figure 5-8 Schematic depiction of the growth mechanism of type-1