Synthesis And Characterization Of Silicon Carbide Nano-whisker By Thermal Evaporation Method

SiC nano-whiskers have not only a wide band-gap, high critical breakdown electrical field, high thermal conductivity, high charge carrier mobility, but also a series of excellent properties due to their low dimensions, leading to important applications in optoelectronics, composite materials, sensors, catalysts and so on. With the ordered array-structure, SiC nano-whiskers may also become a new generation of high resolution display materials and luminescent materials. It is of great significance to study the preparation, performance, growth mechanism and application of SiC nano-whisker arrays in both the scientific research and engineering application.Compared with other reported synthesis methods, a simple and low cost thermal evaporation technique was employed in this paper to prepare SiC nano-whiskers and arrays.β-SiC (3C-SiC) nano-whiskers and their array were synthesized on the different carbon substrates using different raw materials. The phase purity, morphology, crystal structure and defects of SiC nano-whiskers were characterized with X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersion spectroscopy (EDS). The optical, electronic and energy bandgap properties of them were investigated using Raman scattering. photoluminescence test (PL) and the field-emission measurement. The growth mechanism and the relationships between the structure and properties are also discussed based on the above investigation. Some innovative achievements have been obtained and important conclusions are drawn, establishing the fundamentals for the practical applications of SiC nano-whiskers in nano-devices.The results show that the different carbon sources and vacuum levels have some implications to the morphology and array structure of the nano-SiC whiskers. Tube-brush shaped array of SiC nano-whiskers with needle-like tips were obtained around carbon fiber axes, but less regularly arrayed hexagon prism shaped SiC nano-whiskers were grown on the graphite plates. The yields were all high in both cases. For tube-brush shaped arrays on carbon fiber low-vacuum system is needed, but no matter how low or high vacuum, prism shaped SiC whiskers on graphite plate can be always obtained. In a condition of melting, growth temperature has a little effect on the experimental results. Different temperatures have an impact on the growth pace, which is in turn reflected in the length of the whiskers. During different reaction time, the products have obvious distinctions in the appearance, which suggests the different stages of the reaction. From the different appearances and the experiment facts, the formation mechanisms of the SiC nano-whiskers with needle-shaped tips are proposed. Based on the (111) periodic twins in hexagon prism shaped SiC nano-whiskers, a crystallographic growth mechanism for the formation of the periodic twin structure growth is proposed.The down-shifting feature of Raman spectrum of SiC Nano-whiskers shows that there are some stacking faults in Nano-whiskers. The Photoluminescence spectra (PL) peaks of SiC Nano-whiskers are blue-shifted compared with the band gap of bulk 3C-SiC. The phenomena can be explained by the quantum confinement effects of the quasi-periodically twinning superlattice structure formed by the twin stacking faults.Field emission properties of lawny SiC nanowire array on the surface of the polished graphite plate were tested. The SiC nanowire emitters exhibit excellent macroscopic emission properties. It has low turn-on voltage (2.1V/μm) and high brightness.A technique using melt solution of CoSi and CoSi₂ to grow SiC nano-whiskers was also tried by the simple thermal evaporation. The supersaturation of the SiO was controlled by using different metal silicides at the same temperature, thus SiC whiskers with different morphologies were obtained on inner surface of the graphite crucible, and also observed on the surface of the freezed solution. It is believed that the formation of SiC NWs is a combination of solid-liquid-solid (SLS) reaction for nucleation and vapour-liquid-solid (VLS) process for nanowire growth.