Research On Phase Evolution Mechanism And Applications Of Vanadium Oxides Thin Film With Optical And Electrical Properties Changed

The photoelectric window of is important for the photodetector of high-speed aircraft it is more susceptible to interference from high-energy weapons.The protection technology of high-energy weapons is extremely important for infrared optical window.Using its instantaneous high temperature characteristics,a thermochromic coating is deposited on the surface,changing from transparent to opaque,thereby protecting the photodetector.With the complexity of the battlefield environment,windows such as fairings gradually transition from flat to convex.The convex surface can smoothly extend to the signal platform in a streamline shape to reduce air resistance.Achieving the uniform films on convex surface is significant important.In addition,the temperature change characteristics of vanadium oxide resistance can be used for the quenching protection of high-temperature superconducting tapes.Which has a higher resistance at low temperatures,functions as an insulating layer,and stabilizes the magnetic field;When temperature increase caused by quench,the resistance becomes low,and the film layer behaves as a conductor,drawing current to reduce heat.This article takes vanadium oxide film as the main line,studies its high-temperature infrared optical modulation performance and low-temperature resistance change performance,designs and completes different solutions according to different application requirements,which enriches the application of vanadium oxides.At the same time,the impact of transitions between different state of vanadium oxide film states and the its effect on property was monitored in real time.The specific process and main conclusions are as follows:First,the effects of parameters such as oxygen flow rate,deposition time,and deposition temperature on the infrared optical properties of the vanadium oxide film during the deposition process were studied.The vanadium oxide films prepared under different oxygen flow rates mainly contain two components,VO₂ and V₂O₅.With the increase of oxygen flow rate,the V₂O₅ components gradually increase,resulting in the decrease of the infrared optical transmittance and optical modulation performance of the film,42.13%at 0.2 sccm was reduced to 20.26%at 2.0.The increase of the film thickness can also promote the produce of the V₂O₅ composition in the film.The difference is that the vanadium oxide film has similiar phase transition temperature while the transmittance and optical modulation changed,which can benefit different background requirements.Temperature and bias voltage can provide the energy required for crystallization of VO₂.Although the optical transmittance of the film prepared at too low energy can reach 90%,it does not have modulation performance.Too high energy leads to the produce of V₂O₅ and caused the transmittance and modulation performance are reduced.The vanadium oxide film prepared at 500?and-120 V has an optical modulation performance of 76.50%.Secondly,post-annealing was conducted.When annealed in an air environment,due to the presence of oxygen,the VO₂ component in the film is oxidized to V₂O₅ at500?,resulting in the film's infrared optical modulation performance almost disappearing.In the annealing at 600?under nitrogen,the V₆O₁₃ component is formed in the film,which has the low transmittance at room temperature,resulting in the deterioration of the optical transmission performance of the film.The vacuum environment at 500?also also form the V₆O₁₃.Annealing at 500?under nitrogen environment can not only evacuate oxygen,but also avoid the formation of V₆O₁₃,and obtain the best optical modulation performance of?64%.Using variable-temperature Raman and high-temperature FTIR to perform real-time characterization of the performance and structure during high-temperature thermal cycling under nitrogen.It was found that as the temperature increases,the film undergoes a reversible VO₂ phase transition first,and then an irreversible V₂O₅ decomposition occurs at high temperature.This leads to reversible and irreversible changes corresponding to the optical transmittance.At the same time the effect of oxygen partial pressure,film thickness,and substrate materials on the electrical properties of vanadium oxide films at low temperature was studied using a filtered cathode arc vacuum system.The vanadium oxide film has several orders of magnitude resistivity change between low and room temperature.Thirdly,in order to deposit a uniform functional film on convex surface,a model of the deposition rate at any point on the convex surface was established based on the law of the cosine distribution of the Knudsen.Simultaneously,the distribution of different target-substrate distance,target source etch ring size and cosine correction factor on the deposition rate on convex surface was simulated.At the same time,the relationship between step residence time,deposition rate and film non-uniformity is established to realize the parameter design of deposition under the target uniformity.Based on simulation results and deposition parameters of vanadium oxide,a deposition system which could achieve uniform coating on the convex surface was designed and built.After experimental verification,the non-uniformity of the film on convex surface is less than 3%.the comparison of infrared optical transmittance at low and high temperature,the film has optical modulation performance.Finally,through test of I_c before and after coating indicates that the deposition process guarantees the stability of the performance of the superconducting tape.The vanadium oxide film was deposited on the high-temperature superconducting tape,and a test platform was designed and built to complete the characterization of the longitudinal resistance change of the film.The voltage-current test in the superconducting tape with local heating verified that the vanadium oxide film has high resistance at low temperature,which can prevent the current flow between the layer.And the resistance reduced when the local temperature increases,let current flows through the vanadium oxide film layer.So,the vanadium oxide has both the function of insulator and metal,which can apply to quench protection of high temperature superconducting coil.