Study On The Preparation Of Micro-nano Structured VO₂ Thin Film And Its Thermochromic Performance

VO₂ is a kind of polycrystalline transition metal oxide.The reversible transformation of semiconductor phase to metal phase occurs near 68?.In the process of phase transformation,the optical,electrical and magnetic properties will change obviously.Especially,the optical transmittance of VO₂ changes abruptly in the near infrared region before and after the phase transformation,while the visible transmittance(T_vis)is almost unchanged,which is an ideal intelligent material regulating sunshine.Therefore,VO₂ can be applied to smart window research,which has broad prospects in military,industrial,civil and other fields.So far,the phase transition mechanism,preparation methods and functional modulation of VO₂ thin films have been extensively studied.However,the problems of T_vis,low efficiency of solar modulation(?T_sol),high temperature of phase transition(T_c)and color in smart window applications have not been solved.In this paper,a variety of micro-nanostructured VO₂ thin film have been proposed and designed.In the aspects of the balance of T_vis and?T_sol,color control and changing T_c,focus on the mainly following research:Monolayer Si O₂ nanosphere arrays are deposited on sapphire substrates by self-assembly method.Because the surface of Si O₂ spheres is parabolic,which is very similar to the nipple structure of insect compound eyes,the refractive index from the top of the nanosphere to the middle of the side is gradient,which can effectively suppress the reflection of incident light and enhance the transmission of incident light.Therefore,the anti-reflection bionic VO₂/Si O₂ array thin film structure similar to insect compound eye is proposed and designed.VO₂ were deposited on the surface of nanosphere arrays by magnetron sputtering and thermal annealing.The anti-reflection bionic VO₂/Si O₂ array thin film was formed.Compared with the planar compact VO₂thin films prepared under the same conditions,the phase transition temperature was reduced from 61.2?to 42.5?,and T_vis was increased from 24.9%to 43.5%.A method of combining nanosphere lithography technology with magnetron sputtering technology was proposed to prepare semi-perforated VO₂ thin films with Waffle-like structure.By reducing the thickness of VO₂ thin films with periodic semi-perforated structure,T_vis could be improved.This structure is different from the effect of increasing the visible transmittance by simply reducing the thickness of continuous VO₂ thin films which produce the side effect of decreasing?T_sol.Compared with the continuous VO₂ films,the semi-perforated VO₂ films increase T_vis from 8.8%to 42.6%,and?T_sol from 5.9%to 5.5%.This provides a new idea for solving the balance between T_vis and?T_sol.At the same time,the phase transition temperature of the semi-perforated VO₂ films decreases by 6?compared with the continuous VO₂ films due to the effect of decreasing thickness.A method of modifying the transmission spectrum of VO₂ thin films by using the localized surface plasmon resonance(LSPR)characteristics of Au nanoparticles to change the inherent brown-yellow color of VO₂ is proposed.Firstly,V/Au/V sandwich structure was prepared by magnetron sputtering and ion sputtering,and then VO₂/Au/VO₂ sandwich structure was formed by rapid thermal annealing.The obtained results show that with the increasing size of Au nanoparticles,the wavelength and intensity of LSPR change,which effectively modulate the transmission spectrum of VO₂ and the color change from brown to blue-green.At the same time,the T_c of VO₂thin films is reduced to 42.5?due to the effect of electron injection.In summary,by constructing VO₂ micro-nanostructured thin film,this paper aims to solve the problems of low T_vis,low?T_sol,high T_c and color in the field of VO₂-based thermochromic smart windows.The research is constructive to promoting the development of VO₂-based smart windows.