Abstract
Transition metal silicide nanowires compose a highly broad set of refractory materials that are promising materials that are currently used for many applications including CMOS devices, thin film coatings, bulk structural components, electrical heating elements, photovoltaics, thermoelectric and spintronics. Semiconducting silicides have been extensively investigated for silicon-based optoelectronics such as LEDs and IR detectors. The narrow bandgap semiconducting silicides, in particular CrSi2, β-FeSi2, MnSi1.8, and ReSi1.75, have been targeted and used for robust, stable, and inexpensive thermoelectric materials, and have shown potential for photovoltaic applications. β-FeSi2 is a silicon-rich phase with a orthorhombic structure (space group Cmca) that has direct-bandgap . It allows for making light-emitting devices which operate at 1.5mm that incorporate β-FeSi2 into a conventional silicon bipolar junction. ε-FeSi is a metallic material with a cubic structure (space group P213) that has been classified as a Kondo insulator. It has attracted interest for over half a century, mainly because of its unusual magnetic behavior.β-FeSi2 and ε-FeSi nanowires were produced on silicon substrates covered with a thick layer of silicon oxide through the decomposition of the double-source precursor FeCl3 and SiO in a Oxygen Assisted Growth (OAG) process. Unlike typical Vapor-Liquid-Solid (VLS) NWs growth, The NWs form without the addition of metal catalysts had no catalyst tips. The morphologies and structure of NWs were confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). SEM shows that the diameter of the NWs is below 100nm and the length of NWs is tens of micrometers. XRD reveals that samples can grow in single phase or in double phase NWs depending on the growth temperature. Energy spectroscopy for chemical analysis (ESCA) shows the NWs are covered a thick SiO2 layer. TEM results indicate that the NWs growth is along the low index plane. We also have fabricated two-terminal electrical devices of β-FeSi2 and ε-FeSi NWs, and they exhibited average resistivity about 2000μΩ．cm and 250μΩ．cm. We found that the resistivity decreases stepwise as the NWs is thinned in semiconducting nanowires. In conclusion, we have successfully synthesized freestanding single-crystalline nanowires of β-FeSi2 and ε-FeSi by OAG method. This shows that semiconducting and metallic NWs will prove to be promising materials in future nanotechnology.