Preparation And Photo-catalytic Performances Of Hybrid Silicon Nanowire Arrays

As an important new type of semiconductor nanomaterial, silicon nanowires (SiNWs) have attracted much attention over the last decade due to their high aspect ratio, special structure, unique properties and potential applications in broad fields. Photo-catalysts based on hybrid SiNW structures offer several outstanding advantages, such as high electrochemical stability, efficient electron-hole separation, flexible selection of semiconductors with desired band gaps for efficient visible light absorption, and thus have important applications for photo-catalytic degradation of environmental pollutants. In this thesis, we have successfully synthesized hybrid Bi₂SiO₅/Si nanowire and Cu₂O/Si nanowire arrays by decorating the surfaces of silicon nanowires obtained by using the silver-assisted electroless wet chemical etching. The morphologies, microstructures and photo-catalytic performances of as-prepared samples were systematically studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), and ultraviolet-visible spectroscopy (UV-Vis). The summary of this thesis is listed as follows:First of all, Silicon nanowire arrays were successfully synthesized by using metal-catalyzed chemical etching methods. Their morphologies and microstructures were systematically studied. It was found that the SiNWs are regularly arranged with diameters of 30-300 nm and length about 65μm along the intrinsic [100] direction of the single crystalline silicon wafer.Bi₂SiO₅ modified silicon nanowire arrays were fabricated via dip-coating Bi(NO3)3 on silicon nanowires and subsequent annealing. It was found that the length, morphologies and microstructures of pristine silicon nanowires are not destructed during the process. We used the Bi₂SiO₅ modified silicon nanowire arrays as photo-catalysts for photo-catalytic degradation of methyl orange under UV-light irradiation. The results of photocatalytic experiments indicate that the hybrid structures possess superior photo-degradation performance. We proposed that the hetero-structures formed in the hybrid Bi₂SiO₅ modified silicon nanowire arrays enhance the performance due to their efficient electron-hole separation and excellent photo-catalytic stability. Finally, we successfully fabricated hybrid Cu₂O/Si nanowire arrays via depositing Cu on silicon nanowires and subsequent annealing. It was found that the hybrid Cu₂O/Si nanowire arrays retain the length, morphologies and microstructures of pristine silicon nanowires during the process. Using the hybrid Cu₂O/Si nanowire arrays as photo-catalysts for photo-catalytic degradation of methyl orange under visible light irradiation, we found that the hybrid structures possess superior photo-degradation performance. We proposed that the p-n hetero-junctions formed in the hybrid structure enhance photo-catalytic activity and stability due to their efficient electron-hole generation and separation.