Preparation And Characterization Of One-dimensional Silicon Nanomaterials

Quasi one-dimensional nanomaterials have received intensive interests in recent years for their valuable electrical and optical properties, as well as their potential applications in nanodevices. Due to a crucial role of silicon on microelectronics industry, one dimensional silicon nanostructures can be expected to provide a basis for a future generation of nanoscale electronic and photonic devices. Till now, several prototype devices based on silcion nanowires (SiNWs) have been reported, which suggested that one-dimensional silicon nanostructures could be applied as ideal building blocks for the "bottom-up" nanoelectronic manufacturing.In the dissertation, alligned silicon micro-whiskers, silicon nanowires and a few silicon nanochains on silicon substrates were fabricated by chemical vapor deposition (CVD) method, respectively. Employing the nano-channal alumina (NCA) as template, we obtained large-scaled array-orderly silicon nanowires. Furthermore, several types of one-dimensional silicon nanostructures including dendrite nanostructures, nanowires, nanochains, biforked nanowires and nanocrews were synthesized by evaporating the SiO powders. The morphologies and structures of the samples were characterized and analyzed by field-emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), X-ray diffraction (XRD) and Raman spectrum etc. Moreover, the formation mechanisms of the as synthesized nanostructures were discussed. The main results achieved in this dissertation are given as below:We fabricated the alligned silicon micro-whiskers employing silane as precursors and silicon wafers coated by thick gold films as substrates. By altering the hydrogen proportion in ambient gases, large-scale crystalline SiNWs with the controllable diameter were synthesized on silicon substrates coated by thin gold films. Furthermore, array-orderly SiNWs were obtained by NCA templates.A possible growth model is established to explain the effect of hydrogen on silicon nanowire growth. If a lower flux of hydrogen is introduced into the ambient gases, the droplets with the lower surface tension result in small contact angle. Then in the growing stage, according to the VLS mechanism thicker nanowires will be formed due to the supersaturation of silicon. If a higher flux of hydrogen is introduced, then the thinner nanowires will be formed.We obtained the novel silicon dendrite nanostructure by evaporating the SiO powders in vacuum condition. Furthermore, by combining the SiO evaporation with metal catalyst, the uniform and dense silicon nanowires with the diameter of about 20-30 nm and the length of the ten of microns were fabricated. Three types of metal were deposited on the silicon wafer as catalyst. Further research indicates that there is a coexistence of VLS and OAG processes on the metal-coated silicon substrates and VLS process is relatively dominant under our experimental conditions.Silicon nanochains and biforked silicon nanowires were also obtained by thermal evaporation method. The chain-like silicon nano-structures composed of cylindrical section and the oscillating section were observed by FESEM. A typical core-shell morphology including the continuous monocrystalline silicon core and the oxide sheath is illustrated in the TEM image. The obvious transition from oscillation to smooth in the silicon nanochains can be ascribed to the droplet self-oscillation during the VLS growth process. Silicon nanocrews were fabricated by evaporating the mixture of SiO and CNTs powders.