Preparation Of SiC Nanomaterials Using Graphene As Carbon Sources

SiC is the third generation of broadband gap semiconductor materials with properties of high thermal stability, good chemical stability, high critical field, and saturated electron mobility and so on. Comparied with its SiC bulk materials, its nanomaterials possess not only the intrinsic characteristics of the bulk materials, but also the excellent properties of the nanomaterials, such as the size effect, macroscopic quantum tunneling effect, etc., thus SiC nanomaterials are often used in the functional materials and electron devices. There are many methods fabricating SiC nanomaterials, like vapor-solid method, molten salt method, chemical vapor deposition method and laser ablation method, etc. Among these methods, the simplest one is vapor-solid method. Molten salt method could reduce the reaction temperature, heating time, and easy to control the shape ande size of the as-prepared specimens.In recent years, it is the hot spot on preparing SiC nanomaterials when using graphene as the carbon source. There are many studies about growing graphene through SiC decomposition and reversely using graphene as carbon source to fabricate SiC nanomaterials. All the crystal form of prepared SiC nanomaterials on graphene were proved to be single crystal type, 3C-SiC. This thesis focuses on preparing different crystal types of SiC nanomaterials through vapor-solid method and molten salt method by which the whole experiments conduct in the absence of the catalyst. The main work is as follows:(1) In this thesis, SiC nanomaterials with different crystal structures were successfully prepared by the vapour-solid method which the graphene was as carbon source without the catalyst involvement. Meanwhile, the experiment parameters were considered to investigate the effects on preparing SiC nanomaterials which the parameters included temperature, time, crucible, raw materials, and protective atmosphere. The results shows that with the temperature increasing, the diffraction peaks intensity increased at first and decreased subsequently. When the reaction time increased, the diffraction peaks get corresponding increase. Different cystal types are abtained in different crucibles, the samples grow in the corundum crucible have a single crystal form: 2H-SiC, while the samples fired in the graphite crucible possess two crystal types 3C-SiC and 2H-SiC. In the atomsphere of Ar, the crystal types of 3C-SiC and 2H-SiC could be obtained at 1400℃ in the graphite crucible, while in high vacuum of 10-3pa, only 2H-SiC can be attained.(2) This paper have used different molten salts to make SiC nanomaterial in the condition of making Si powder and graphene as the raw materials and the mechanism of experiment has also been studied. The results show that NaCl is the most suitable for the preparation of SiC nanomaterial among LiCl-KCl, NaCl-NaF and NaCl molten salts. NaCl not only is a corrosion free molten salt, but also possesses high melting point, which can make molten salt in slow evaporation. The mechanism of the preparation of SiC nanomaterial in NaCl molten salt is vapour-solid, Si powder in NaCl molten salt evaporated and reacted with graphene suspended in the top of NaCl molten salt.(3) Both Magnesium reduction to prepare SiC nanomaterial and the experimental conditions has been studied. The results shows that the NaCl molten salt is suitable for the experiments and when the mole ration of SiO2, Mg, C is 1:2:3, none of Si material apprear in the final prepared product, and the crsral form of the fabricated SiC have been proved to be 2H-SiC.