SiC Nanowires by Silicon Carburization
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0963-Q11-03
SiC Nanowires by Silicon Carburization Loucas Tsakalakos, Jody Fronheiser, Larry Rowland, Mohamed Rahmane, Michael Larsen, and Yan Gao General Electric Global Research Center, Niskayuna, NY, 12309 ABSTRACT Polycrystalline SiC nanowires and composite Si nanowire-SiC nanograin structures have been synthesized using a combined catalytic chemical vapor deposition and carburization method. Si nanowires are grown at low temperature (550-650 C) and subsequently carburized at 1100-1200 C in a methane/hydrogen or propane/hydrogen environment. Thermochemical calculations showed that the Si carburization is thermodynamically favorable over a wide temperature range, whereas our studies showed that the Si nanowire carburization is kinetically limited below ~1100 °C. Partially carburized nanowires contained distinct SiC nanosized grains on the Si nanowire surface, whereas fully carburized nanowires were polycrystalline 3C SiC with grain sizes of ~ 50100 nm. INTRODUCTION Nanowires and related one-dimensional nanostructures have recently been shown to be important building blocks for nanosystems with significantly improved or completely new performance capabilities compared to micro-devices. Nanoscale devices such as field effect transistors [1,2,3], UV sensors [4], chemical sensors [5], and biosensors [6] have been demonstrated. SiC nanowires have been the subject of particular interest due to their wide-bandgap (Eg = 2.2 eV), high electron mobility (1000 cm2/V-s), high breakdown field, and high temperature stability, making them promising candidates for nanoscale UV LEDs, harsh environment sensors, and electronics. While most SiC nanowires materials studied are nominally single crystals, polycrystalline SiC nanowires may also be of interest as toughening elements in mechanical load bearing nanocomposites or as field emitters. Numerous methods for synthesizing SiC nanowires have been described in the literature. These include metalorganic chemical vapor deposition (MOCVD) [7], microwave plasma CVD [8], direct heating of substrates [9] nanotube confined reactions [10] thermal evaporation of powders [11], hot filament CVD [12] and sputtering combined with rapid thermal annealing [13]. More specifically, Kang et al. [7] used MOCVD with dichloromethylvinylsilane as the precursor, which supplies both the Si and C species required, whereas Lin et al [8] used tetramethyl silane and hydrogen in a microwave plasma reactor. Both works utilized Ni as the seed catalyst for nanowire growth, i.e. with the vapor-liquid-solid mechanism being operative [14]. It has also been
shown that it is possible to grow SiC nanowires on Si using the substrate as the Si source. Kim et al. [9] achieved such direct growth using Ga and GaN as the precursor with Fe as an additional catalyst, and Zhang et al. [15] formed SiC nanowires by flowing hydrogen and methane over an iron-coated Si wafer in a microwave plasma CVD reactor. Finally, Pan et al. [10] reacted carbon nanotubes (CNT) with SiO and Ar at 1400 °C to form SiC nanowires, with the CNTs act
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