3 C - And Luminous Performance Study Of Preparation Of Sic Nanowires

Cubic silicon carbide (3C-SiC) has excellent mechanical, thermal, optical and electric properties, which make it attractive for the devices designed to operate at high power, high temperature, high voltage, high frequency and harsh environment. In comparison with bulk3C-SiC,3C-SiC nanowires have more excellent performances, and some properties absent in bulk materials. This thesis is of two parts. The first is about synthesis of3C-SiC nanowires, including the effects of different raw materials and experimental conditions on the structure and morphology of products, and the investigations on the growth mechanism, and photoluminescence properties of the samples. Second part is about the synthesis and photoluminescence of Si nanocrystallines. The main results are as follows:1. Milled Si powders are mixed with activated carbon with the molar ratio of1:4,1:2, and1:1, respectively.3C-SiC nanowires are prepared by heating the mixture at1300℃for4hours with the portection of Ar gas under atmospheric pressure, and following heating in air. The sample synthesized at the molar ratio of1:2is of3C-SiC nanowires with pure structure and uniform morphology. The length of the nanowires is about tens micrometer, and the radius is tens nanometer. Residual oxygen in the reaction system plays a key role during the nucleation and formation of products. The growth mechanism is releated to vapor-solid and vapor-gas mechanics with oxygen-assistiant. There are two peaks resided at416and439nm in the photoluminescence line of the nanowires.2. Large quantities of3C-SiC nanowires are synthesized at the atmospheric pressure with the protection of Ar gas form the ball-milled SiO powders and activated carbon, which are stacked in an alumina boat separately. The samples on the surface of activated carbon are of pure3C-SiC. At the synthesis temperature of1250and1300℃,3C-SiC nanowires with the length of tens micrometer and radius of tens nanometer are observed. A higher temperature at1350℃results in the nanowiers together with nanoparticles. The nucleation of3C-SiC nanowires relates to vapor-solid reaction between SiO vapor and activated carbon, and the growth relates to vapor-gas reactions between SiO vapor and CO gas. Two peaks reside at416and439nm in the photoluminescence line of the nanowires.3. The silicon nanocrystals in benzene, de-ionized water or ethanol are fabricated via a chemical etching of silicon powders in mixture solution of HNO3and HF followed by the ultrasonic vibration. The silicon nanocrystals have an average size of about2nm, which are suspend in the solutions or surrounded in the amorphous shell. The photoluminescence band of Si nanocrystals are detected in toluene, de-ionized water and ethanol. With the invreasing excition wavelength, the intensity of photoluminescence peak increases at first, then decreases. Meanwhile, the position of photoluminescence peak redshifts monotonously. Excited at the same line, the Si nanocrystals suspended in benzene have the stongest emmission, while the photoluminescenece in ethanol is weakest.