Porous Vanadium Dioxide Film Prepared By Magnetron Sputtering And Its Performance Optimization

M phase VO₂ undergoes a well-known reversible metal-insulator transition（MIT）at 68℃,with a huge and ultrafast change in infrared transmittance.Based on this feature,the applications of VO₂ thin film to building windows can realize intelligent control of the solar energy.But in the actual application of VO₂ thin film,there still exist some problems such as low visible light transmittance and solar modulation efficiency,it is difficult to improve both of them at the same time.Through computer simulation,researchers found scatter VO₂ particles in electrolyte or introduce pores into films can significantly improve the visible light transmittance and does not reduce the solar modulation efficiency.As a well-developed industrial fabricating method,magnetron sputtering method has many advantages.Hence,preparing porous structure VO₂ films by magnetron sputtering method is of great significance for realizing the commerical application of intelligent window.This paper using dual magnetron sputtering method and slant magnetron sputtering method to fabricate porous structure VO₂ thin filmon quartz glass.The influence of annealing parameters and different carbon content on the thin film optical performance were studied.Through the way of adding buffer layer on the common glass substrate,excellent properties of VO₂ thin film was obtained and the different buffer layer were compared.Specific content are as follows:（1）Using dual target sputtering method,through the optimization of carbon content and heat treatment parameters,thin film with best performance which T_lumum andΔT_sol are 40.4%and 6.8%respectively is obtained under the condition of the sputtering power of carbon and vanadium are 50 w and 77 w,sputtering time 15 min,heat treatment temperature of 400℃,air pressure 500 pa and heat treatment for 2hours.By XRD and SEM characterization,we find that with the increase of carbon content,crystalline of VO₂ reduced,according to the position of the diffraction peak,a small amount of C get into VO₂ crystal lattice and replace the position of O atom;In addition,with the increase of carbon content,the density of the film decrease,the grain morphology transform from a mixture of the long bar and tiny particles to pure tiny particles,and the content of the porosity in thin film increases gradually.（2）The angle of deposition has great influence on optical properties and microstructure of the films.With the increase of the angle from 0^o to 60^o,visible light transmittance increased but the solar modulation efficiency decreased.According to the microstructure it may be result from surface roughness,disordered and uneven distribution of particles.（3）Through the way of adding buffer layer,VO₂ thin film can be prepared on float-glass substrate,the key is to prevent the diffusion of sodium ions in glass substrate,and the buffer layer with similar crystal structure can also induce VO₂crystal formation.For the good thermal conductivity,thermal expansion coefficient between the glass substrate and VO₂ thin film,VO₂ thin film prepared on FTO owns a lower transition temperature than theory,and visible light transmittance is higher than the film prepared on silicon glass,but obviously,the amplitude of near infrared adjustment decrease.Moreover,increasing deposition temperature leads to a higher transition temperature.