Water-assisted synthesis of silicon oxide nanowires under supercritically hydrothermal conditions

Abstract

Large-scale amorphous silicon oxide nanowires (SiONWs) have been synthesized from silicon monoxide powder under supercritically hydrothermal conditions. The chemical bonding of amorphous SiONWs were investigated with Fourier-transform infrared (FTIR) spectrometry and near-edge x-ray absorption fine structure (NEXAFS) spectrometry. Our results show that the SiONWs are tens of microns long with a diameter from tens to hundreds of nanometers. Selected area electron diffraction (SAED) shows that the samples are amorphous. Energy dispersive x-ray spectrometry (EDX) analysis reveals that the SiONWs consist of Si and O elements in an atomic ratio approximately equal to 1:1.5. The results of FTIR and NEXAFS indicate that some OH groups are located on the surface of the SiONWs in the form of Si–OH. The relation between the chemical bonding and the possible growth mechanism was also discussed. During the growth process, water is an important species, which can provide H+ and OH− under supercritically hydrothermal conditions. The H+ and OH− block the defects of Si–O• and Si•, respectively, in the form of Si–OH and stabilize the structure. The Si–OH can reduce the adsorption activity of the SiONW surface which may be in favor of preventing the growth from the cross section and assisting the growth along the axial direction of the SiONWs.