Crystal Preparation And Temperature-Resistance Characteristics Of Vanadium Dioxide

Vanadium dioxide is a semiconductor oxide which has important applications in infrared detection,smart windows,gas sensing devices,infrared optical switches and field-effect devices.The application of vanadium dioxide is based on the large variation of temperature-resistance characteristics of the material.The most widely known characteristics is the metal insulator transition?MIT?characteristic of M phase VO₂ at 68?.Although the properties of large area polycrystalline VO₂ films prepared by magnetron sputtering have reached the requirements of application and commercialized,continuous pursuit of the high performance of the devices and the need for in-depth scientific research raise requirements for large area,high crystallinity and high performance VO₂ single crystal thin films.In this thesis,the effects of different preparation conditions on the structural and temperature-resistance characteristics of VO₂ with different phases are systematically investigated,and the important factors affecting the growth of high quality VO₂ are revealed.Based on the existing model,we analyze the process of material growth and the temperature-resistance characteristics to figure out the way for preparing high quality VO₂.The main contents and results of the thesis include the following three aspects:?1?using V₂O₅ as the source material,vanadium dioxide microcrystal was prepared by chemical vapor deposition without catalyst.The effects of preparation temperature,sample location,vacuum and substrate on the morphology of the prepared samples were studied in detail.The optimum preparation conditions of VO₂ were determined.According to this method,large scale vanadium dioxide nanosheets with tens of microns in size can be obtained.The variable-temperature Raman spectroscopy test showed that the sample had obvious MIT characteristic,but the phase transition was not uniform because of the influence of the substrate.?2?In the above research process,it is found that V₂O₅ source is changing to VO₂.Using this characteristic,mm grade VO₂ single crystals have been successfully prepared using Al₂O₃crucible.The MIT temperature is⁶8?,temperature hysteresis is³?,and the resistance change is 10⁴ orders of magnitude,showing that the material has high quality.The above results are explained according to the phase diagram of vanadium dioxide.?3?the effects of the reaction temperature,reaction time and the quantity of the precursor materials on the preparation of B phase vanadium dioxide were studied in detail by solution deposition.High quality B phase vanadium dioxide crystal film was prepared.The temperature-resistance characteristic of the material is measured and the temperature coefficient of resistance?TCR?of the material is found to be anisotropic.In the?001?plane,the TCR value at 280 K is-3%/K,which meets the application requirements of the microbolometer type infrared detector.In the direction normal to the?001?surface,the TCR value is only-1.7%/K.Further study on the temperature dependence of the IV curves shows that the temperature-resistance characteristics are anisotropic,temperature dependent and voltage dependent.We give a preliminary explanation of this phenomenon.