Synthesis And Characterization Of One-dimensional SiC Nano-materials

Silicon carbide (SiC) belongs to the third generation wide band gap semiconductor material. It possesses unique properties such as high thermal conductivity, high electron saturation drafting velocity, high breakdown electric field, low concentration of intrinsic charge carriers, high radiation-resistance, and chemical inertness and so on. These excellent physical properties make SiC a promising material for device applications at high temperature, high power, high frequency, and in harsh environment. It also has received much attention due to these unconventional properties since 1990s. Besides the properties of block SiC materials, one-dimensional nanometer sized SiC exhibits extra optical and electrical properties due to its nanometer dimension, and consequent quantum confinement effect and surface effect. It has become one of the most important materials in the semiconductor field along with the development of nanoscale electric devices and measurement.Based on the research history of SiC and the merits and demerits of various producing methods, we developed a simple heating method to synthesize one-dimensional SiC nanomaterials. In this method, carbon nanotubes or carbon black was used as the carbon source. It reacted with silicon contained atmosphere created by the silicon to form one-dimensional SiC nanostructures. The silicon source was always separated from the carbon source during the whole process. By altering temperature, time, the distance between carbon source and silicon source, and adding catalyst, how the reaction condition influences the morphology and structure of the products was investigated. The morphology and structure of the products were characterized and studied by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, and so on. The growth mechanism of the products is also discussed on the basis of the investigation. The results are significant to practical production of one-dimensional SiC materials in large scale.By altering the reaction conditions, it is found that as the reaction temperature and time increase and the distance between carbon source and silicon source decreases, the yield of one-dimensional SiC nanomaterials increases. After adding Fe as the catalyst, the yield can be improved; however, the impurity is then introduced. The growth mechanisms with and without catalyst follow the vapor-liquid-solid (VLS) andvapor-solid (VS) mechanism, respectively. However, both the growth direction is [111] and the growth is realized by piling up atoms onto (111) plane because the (111) planer has the lowest surface energy.Carbon black and silicon powder reacted with each other to produce prism-shaped SiC nanowhiskers, but the reaction needed a higher temperature compared to the reaction between Si and CNTs. Smooth prism-shaped SiC nanowhiskers were obtained after the reaction at 1500 ℃ for 12 hours, while rough prism-shaped SiC nanowhiskers were gained after the reaction at 1550 ℃ for 3 hours. The roughness of the surface may be related to heating time. The blue shift of LO phone line in the Raman spectrum may be possibly caused by the defects and the size confinement of one dimensional SiC nanostructures.Because of the participation of oxygen, low temperature (1200 ℃) reaction of silicon and carbon nanotubes led to the formation of pearl-like SiC nanowires, SiC nanowires and SiC/SiO₂ nanocables at different location of the graphite. Pearl-like SiC nanowires were formed by the combined effect of the growth velocity, the stem radius of the nanowire and the supersaturation degree of SiC in the catalyst droplet. The formation processes of SiC nanowires and SiC/SiO₂ nanocables can be explained by the calculation of the Gibbs free energy change (â–³_rG). It is concluded that SiC and CO₂ or SiC and SiO₂ can be obtained by the reaction of SiO and CO below 1200 K, while only SiC and SiO₂ can be obtained above 1200 K.As shown in the above studies, one-dimensional SiC materials with various morphologies and structures can be synthesized by altering reaction conditions. The method here is simple, the source materials are easy to get, and the yield is high. All these advantages are favorable for the production of one-dimensional SiC materials in large scale.