Preparation of silicon nanowires by hydrothermal and its physical properties

Intrinsic silicon nanowires were prepared using hydrothermal method, with high activity silicon oxide powder (SiO) as raw material and deionized water as reaction medium, made through recrystallization and nucleation growth of the silicon atom in high temperature and high pressure supercritical water thermal environment in high pressure reaction kettle. The best hydrothermal conditions to prepare silicon nanowires were explored. It showed that the best condition of hydrothermal preparation of silicon nanowires was temperature of more than 450°C and pressure of 9~10 MPa by multiple experiments exploration. Through the scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDX) and high resolution transmission electron microscopy (HRTEM), the morphology and structure of SiNWs were observed and analyzed, and its components were analyzed. SEM showed that the surface of silicon nanowires was smooth, and its minimum diameter was 50 nm and its length was about 3 ~5 μm. It could be seen that SiNWs was made up of only silicon and oxygen elements, and silicon and oxygen atom number ratio was 3.5:1.0 by EDX image. Under the HRTEM, it showed that silicon nanowires was composed of crystalline silicon structure in the core and external amorphous silica cladding layer less than 5 nm. The Raman spectrum of intrinsic SiNWs showed that the Raman main peak occurred blue shift and asymmetric widening in low frequency due to the stress pressure and defect in SiNWs. The growth mechanism of preparation SiNWs by hydrothermal could be explained on the basis of experiment. SiO in water thermal environment reaction formed silicon and silicon dioxide by disproportionation, then Si and SiO₂ began to stack formation a large number of nano clusters Si_xO, and silicon atom recrystallized in a certain temperature, at the same time, the nanowires grew under the guidance of the Si_xO SiNWs along the one dimensional direction.