Vacuum Vapor Preparation And Growth Mechanism Of Semiconductor Nanomaterials

Recently, research on one-dimensional (1D) nanomaterials has become one of the research frontiers and focuses of the nanomaterials field. 1D semiconductor nanomaterials are of great importance for not only fundamental researches but also the construction of functional nanodevices due to their unique physical-chemical properties. They have attracted great attention and developed rapidly in the past twenty years. An essential problem in 1D nanomaterials researches is to develop the efficient and convenient synthesis techniques. In the other hand, inspecting the native growth mechanism of materials will benefit and direct the synthesis work.Chemical vapor deposition, an important synthesis method for effective synthesis of nanomaterials, was developed very well in resent years. In this thesis, a novel vacuum chemical vapor reaction (CVR) method, which is low-cost, convenient-operated, and environment-friendly, was designed for the synthesis of semiconductor nanomaterials. Various semiconductor materials have been obtained through this method.The two kinds of important semiconductors chalcogenide and silicon were chosen as the study system on the basis of literature. The process of synthesis, morphology characterization and growth mechanism of their nanostructures were investigated in detail. This research is of great importance for the evolution of nano-semiconductor science and technology. The main results presented in the thesis are as follows:1. Synthesis of vertical standing CuS nanoplates on flat substrate via vacuum CVR method. This result provided a theoretic foundation for the fabrication of novel structured nanodevices. The morphology and crystal structure were investigated by SEM and TEM. It was found that the orientation of CuS nanoplate perpendicular to the substrate surface was decided by the native anisotropy characterization of CuS.2. Through the vacuum CVR process, we prepared flexible Cu2Se nanowires with two different structures that are determined by whether to be catalyzed by gold. The nanowires obtained from the sample that was not catalyzed by gold membrane are mono-dispersed with a global particle at the tip of each wire. It is found that the component of wires and the particles are quite different, thus it is concluded that the nanowires were not epitaxially grown from the particles, however, the particles play the roll of catalyst in the reaction which is similar to the solid-liquid-solid process. The growth direction of gold-catalysed nanowires is well oriented, depending on the crystal structure of the growing center of the nanowires. The two kinds of nanowires both have a uniform diameter of about 50 nm and an average length of 50μm. Our research indicates that the nanowires have a single crystal face-center cubic structure. By using the SEM, it is detected that the growth mechanism of the two kinds of nanowires follows different pathways. The preparation of Cu2Se nanowires represents the experimental template for the exploration and application of 1D nanomaterials. The selenide might become an important substitute for the energy transition materials.3. Fabrication of regular oriented single-crystalline silicon sub-micron wire arrays through the CVR method. The existence of Ag2Te particles on the tip of the nanowires indicates the formation of silicon sub-micron wires follows the vapor-liquid-solid growth mechanism. A main difference from the classic VLS mechanism in our experiment is that the vaporous silicon resources were obtained via the prior chemical reaction between silicon substrate and Te vapor at high temperature but not introduced by blowing a Si contianing vapor (such as silane). The results of this study have greatly enriched the VLS growth mechanism and its application, and the vapor reactants of VLS reactions are no longer limited to the gaseous or volatile materials. In addition, the catalyst we choose is Ag2Te, which has not been reported as a catalyst of nanowire growth in literature. So the application of chalcogenides is expanded in the catalytic area.The perfect combination of chalcogenides and silicon nanostructures will bring new properties. It is worth being researched further. One significant characteristic of Ag2Te catalyzing is that it changed the common (111) growth direction of silicon wires, representing a new method of controlled synthesis.