The Growth And Properties Research On SnO₂ Nanowires

As an n-type semiconductor material with direct wide band gap, SnO₂ was widely used in transparent conductive glass, solar cell, flat panel display, high-temperature electronic devices, gas sensors and other fields. Due to its excellent optical and electrical properties, SnO₂ with One-dimensional structure has broad potential application in optoelectronic devices, Ultraviolet (UV) laser system and many other fields, which attracts wide attention of the researchers. In this paper, we report the synthesize method, structure properties, growth mechanism and the field emission property of the tin oxide nanowires. The principal elements are listed as follows:1. Using vapor transport method, high-quality SnO₂ nanowires was made on the silicon substrate in a lower temperature (850°C) with high-purity N₂ as carrier gas, Au as catalyst, and the compound of SnO₂/SnO and graphite powders as starting materials respectively. We research the microstructrue and the surface morphology using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the selected area electron diffraction (SADE). It could be learned that the starting materials had great relationship with the microstructrue and the surface morphology features of the nanostructure of SnO₂. Use the mixture of SnO₂ and carbon for source materials, we produced long and straight nanowires whose diameters were between 50-200 nm. The nanowires produced by SnO and carbon had wide variety of structures such as straight-line, V-shape, Y-shape et al. Their diameters were about 150 nm.2. We studied the function of Au catalyst on the nanostructure morphology of tin oxide. The results showed that the catalyst play a very important role in the preparation of the nanostructure of tin oxide. The trial proved that it needs catalyst in the preparation of tin oxide nanostructure in a relatively low temperature. Or it would be very difficult to fabricate a single crystal structure without catalyst. The larger thickness of the catalyst, the larger diameter of the nanowires. We can control the location and scale of tin oxide nanowires by control the distribution and thickness of the catalyst on the substrate.3. The entire growth process of tin oxide nanowires had been seen clearly with controlling the reaction time, and its growth mechanism was studied. In high temperature, the catalyst Au films contracted into clusters. The larger of the Au films thickness, the larger of the cluster size. When the vapor product was transported to the substrate by carrier gas, the Au cluster reacted with the vapor product and produced melted alloy droplets firstly, and then formed crystal nucleus. The nanowires began to grow from the bottom when the reactant in droplets was saturated. If there is still reactant and the alloy droplets aren't solidified, the nanowires can continue to grow. The alloy droplets solidified in the top of the nanowires when the system was cold. The growth mechanism of the SnO₂ nanowires in our experiment follows the conventional vapor-liquid-solid (VLS) growth mechanism.4. We studied the field emission characteristics of the tin oxide nanowires with different morphology as the cold cathode. As reported, the tin oxide nanowires have a lower turn-on and threshold electric field than the zinc oxide and SnO₂ arrays have. The threshold electric field is 2.5-3 V/μm. It is a good material for field emission, but its stability is not very well and its F-N curve is nonlinear. Further intensive investigation is needed.