Synthesis And Characterization Of Silicon And Silicide Nanostructures

One-dimensional (1D) nanostructures have attracted much attention owing to their high aspect ratio, anisotropy, special structure and unique properties. The researchers focus their attention on how to control the morphology of the product, exploit the mechanism of growth process and investigate or improve the properties of the nanostructures. Silicon is a wonderful material for modern electronic devices and there has been intense research on various aspects. The continuously shrinking size of silicon devices has raised interest about the properties of silicon at the nanoscal. Bright luminescence in silicon was first discovered in the form of porous silicon and it became a useful materials for optical application. During the past few years, silicon and silicide nanostructures have been successfully synthesized. However, systematic investigations such as the growth conditions and growth mechanism have not been studied. Moreover, much effort shoud be focused on how to control the morphology and improve the properties of the nanostructures.Based on reviewing the recent progress of 1D silicon and silicide nanostructures, single crystal silicon nanowire, flower-like silicon nanostructures, silicon oxide hierarchical nanostructures, macropores on silicon, nickel silicide nanowires, iron silicide nanowires and silicon oxide nanotube have been prepared by thermal evaporation or chemical vapour deposition method (CVD). The optical, electrical and magnetic properties of these nanostructures have also been investigated.1. Silicon nanowires have been synthesized on silicon substrate and alumina (NCA) templates using Au as catalyst by CVD method. The diameter of the silicon nanowires can be controlled by the temperature and the pore diameter of the NCA. The waveguide properties of the silicon nanowires are very well due to their smooth surface and uniform diameter. Flower-like silicon nanostructures have been prepared by thermal evaporation method on silicon substrate using Au as catalyst. While, the silicon nanowires with small diameter can be obtained on silicon substrate without Au. Light emission of the flower-like nanostructure has been observed, which is considered to be the enhanced photothermal effect. The PL property of silicon nanowires synthesized by thermal evaporation method was also studied. The emission located at 450 nm was attributed to the oxide layer on the surface of silicon nanowires.2. SiO₂ hierarchical nanostructures consisting of a wire-like main stem and lots of rod-like sub-branches have been synthesized by a magnesium catalyzed thermal evaporation process. It is indicated that magnesium plays a critical role in the synthesis of SiO₂ hierarchical nanostructures including promotion for SiO evaporation and hierarchical-like growth of SiO₂. Moreover, the PL analysis of the SiO₂ hierarchical nanostructures reveals that blue and ultraviolet (UV) emissions are detected, which are different from those of other SiO₂ nanostructures. The growth mechanism and PL emission of SiO₂ hierarchical nanostructures have been discussed.3. A novel hydrofluoric acid free atmospheric pressure chemical vapour deposition method has been developed to synthesize macropores on silicon. The growth mechanism of the formation of the macopores has been discussed. The PL spectra of the macropores show a broad emission band with the peak position at 402nm, which is related with the defects of silica. Based on the growth mechanism, we synthesized the pores on silicon with small diameter by rapid thermal process (RTP) method. Moreover, the diameter can be controlled by the thickness of Sn film on silicon and the reaction time of RTP.4. Uniform nickel silicide nanowires have been prepared on Ni foil, foam Ni, Ni grade and silicon with Ni film by CVD method. The morphology of the product can be control by the growth conditions such as temperature, pressure, gas flow ratio and reaction time. Moreover, the arrayed nickel silicide nanowire can be obtained under an appropriate experiment condition. These nanowire arrays have good field emission property. The nickel silicide nanowires on Ni foam show good lithium ion battery performance because of high surface area ratio and good electron conductive property. A Ni diffusion controlled mechanism is proposed to explain the formation of the nickel silicide nanowires.Iron silicide nanowires have been prepared by thermal evaporation method. The effects of the gas flow ratio and growth time on the morphology and structures have been studied. Silica nanotube can be formed under an appropriate condition. The magnetic property of iron silicide nanowires was also investigated.