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采用水热法在高压反应釜内的高温、高压超临界水热环境下,以去离子水为反应介质,使活性高且难溶于水的一氧化硅粉末(SiO)通过硅原子的重结晶成核生长出本征硅纳米线。通过温度控制仪控制高压反应釜内温度和压力的变化,探索制备硅纳米线的最佳水热条件。通过多次实验探索,得知水热法制备硅纳米线的最佳条件是温度大于等于450℃、压力在9～10 MPa。然后通过扫描电子显微镜(SEM)、能量色散X射线光谱仪(EDX)、高分辨透射电镜(HRTEM)观察SiNWs的形貌和结构,分析其组成成分。通过SEM可观察到硅纳米线表面光滑、最小直径达50 nm及长度为3～5μm,由EDX图像可知SiNWs中只有硅和氧两种元素,而且Si∶O原子数比为3.5∶1.0。在HRTEM下可知硅纳米线是由芯部的晶体硅结构和外部无定形的二氧化硅包覆层组成,且包覆层小于5 nm。研究了本征SiNWs的拉曼光谱,发现拉曼主峰蓝移且在低频发生不对称宽化,分析认为是硅纳米线中存在的压应力和缺陷导致的。同时,在实验的基础上解释水热法制备SiNWs的机制,SiO在水热环境下歧化反应生成硅和二氧化硅,然后Si和SiO2开始堆叠生成SixO,即大量的纳米团簇,在一定温度下硅原子重结晶,同时在SixO的引导下沿一维方向生长。
Hydrothermal method is adopted in the high-temperature and high-pressure supercritical hydrothermal environment in a high-pressure reactor to use deionized water as a reaction medium to make silicon oxide powder with high activity and hardly water-soluble (SiO) recrystallized through silicon atom Nucleated silicon nanowires were grown by nucleation. The temperature and pressure in the autoclave were controlled by a temperature controller to explore the optimal hydrothermal conditions for the preparation of silicon nanowires. Through many experiments and exploration, we know that the optimum conditions for the preparation of silicon nanowires by hydrothermal method are temperature of 450 ℃ and pressure of 9 ~ 10 MPa. The morphology and structure of SiNWs were observed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and high resolution transmission electron microscopy (HRTEM). It can be observed by SEM that the surface of the silicon nanowires has a smooth surface with a minimum diameter of 50 nm and a length of 3 to 5 μm. It can be seen from the EDX images that SiNWs contain only two elements of silicon and oxygen, and the atomic ratio of Si: O is 3.5: 1.0. It is known from HRTEM that silicon nanowires consist of a crystalline silicon structure of the core and an outer amorphous silica cladding with a cladding of less than 5 nm. The Raman spectra of intrinsic SiNWs were investigated. It was found that the main Raman peaks were blue-shifted and asymmetrically broadened at low frequency, which was considered as the result of compressive stress and defects existing in SiNWs. At the same time, the mechanism of hydrothermal preparation of SiNWs was explained on the basis of experiment. SiO reacted in water and heat to form silicon and silica. Then Si and SiO2 began to stack to form SixO, that is, a large number of nanoclusters. At a certain temperature Under the silicon atoms recrystallization, while in the SixO under the direction of one-dimensional growth.