Synthesis And Properties Of Silicon Nanowire Arrays

Silicon is a indirect band gap semiconductor, whose light-emitting efficiency is very low. Due to the size-dependent quantum confinement, silicon nano-materials become direct band gap semiconductors and light-emitting efficiency increases. They have attracted great interest in the last few years for important applications in nanoscale electronic devices and biomedical field. Until now, there have been various methods for synthesizing silicon nano-materials. But how to synthesize silicon nano-materials using simple and industrial methods is a problem. In additon, semiconductors have band gaps to absorb light over a wide spectral range, so they can be used in degrading organic pollutants as photocatalysts. Silicon is a main group semiconductor material, whose nanostructures also have photocatalytic activity. In this paper, we focus our research on the synthesis of silicon nanowire arrays and photocatalytic studies of porous silicon nanowire arrays.1.We fabricated large-area aligned silicon nanowire arrays by one-step chemical etching method using HF and AgNO3 etching solution. The influence of the concentration of silver nitrate and hydrofluoric acid, temperature and etching time on the morphology of silicon nanowire arrays was discussed by altering the experimental parameters. According to the influence of the various experimental parameters on the morphology of silicon nanowire arrays, we obtained the optimal synthesis technology parameters as following:HF concentration:3.6-4.8 M, concentration of AgNO3: 0.01-0.02 M, synthesis temperature:25-50℃, synthesis time:30-60 min. The XRD results demonstrated that silicon nanowire arrays retained the crystal structure of the starting silicon wafer. In addition, the raman spectra and reflectance spectra of silicon nanowire arrays were characterized. The formation mechanism of silicon nanowire arrays were analyzed briefly.2. Porous silicon nanowire arrays were fabricated from highly doped silicon wafers by a two-step metal-assisted chemical etching method. The morphology and structure of porous silicon nanowire arrays were characterized by SEM and HRTEM. The results confirmed porous silicon nanowire arrays retained the crystallographic orientation of the starting silicon wafer and there were many pores whose diameters were approximately in the range of 2-20nm on the surface of silicon nanowires. The H-terminated, Pt-modified and Au-modified porous silicon nanowire arrays were obtained by a facile chemical method. The surface structure, chemical composition of different surface modified porous silicon nanowire arrays were characterized by FTIR, XRD and SEM.3. The photocatalytic activity of different surface modified porous silicon nanowire arrays was evaluated by the photodegradation of rhodamine B and methylene blue. We found that the relative intensity of the absorption peaks of rhodamine B diminishs little in the presence of as-prepared, Pt-modified or Au-modified porous SiNW arrays, while the absorption peaks under H-terminated porous SiNW arrays diminish more. So the potocatalytic activity of porous SiNW arrays is improved remarkably by HF treatment. But metal modification improved hardly the potocatalytic activity of porous SiNW arrays. The photocatalysis mechanism of the H-terminated porous Si nanowire arrays was investigated. Good photocatalytic activity of H-terminated porous silicon nanowire arrays was demonstrated. This property lied in the Si-Hx bonds on the surface of porous silicon nanowire arrays. It makes silicon nano-materials have a potential application in photocatalysis.