Large-Area Synthesis and Microstructural Investigations of Silicon Nanowires and Te/Bi<sub>2</sub>Te<sub>3</sub>-Si Core-Shell Structures

Abstract

Large-area randomly-oriented silicon nanowires (SiNWs) were synthesized using Au-coated p-type Si (100) substrates via the solid-liquid-solid (SLS) process under different growth conditions. Microstructural studies on the NWs produced showed that straight crystalline nanowires of large aspect ratios were generally obtained at a growth temperature of 1000°C along with some worm-like amorphous structures. Large-area vertically aligned silicon nanowire (SiNW) arrays on p-type (001) Si substrates were also synthesized in an aqueous solution containing AgNO3 and HF by self-selective electroless etching. Diameters of the SiNWs produced from both methods varied from 50 nm to 350 nm and their lengths generally extended from several to approximately a few tens of µm depending on the growth conditions used. Te-Si and Bi2Te3-Si core-shell structures were subsequently obtained via galvanic displacement of SiNWs in acidic HF electrolytes containing HTeO2+ and Bi3+/HTeO2+ ions. The reactions were basically a nanoelectrochemical process due to the difference in redox potentials between the materials. The modified SiNWs of core-shell structures had roughened surface morphologies and, therefore, higher surface-to-bulk ratios compared to unmodified SiNWs. They should have potential applications in sensors, photovoltaic and thermoelectric nanodevices. Microstructural studies on the SiNWs and core-shell structures produced are presented using various microscopy, diffraction and probe-based techniques for characterization.