Microstructure And Thermochromic Properties Of VO_x/HfO_x Composite Films

The phase transition process of VO₂ is accompanied by abrupt changes in optical properties,which enables VO₂ to have the ability to modulate sunlight energy and become an ideal thermochromic smart window material.Although the modulation amplitude of the pure-phase VO₂ film to near-infrared light exceeds 50%,due to the serious intrinsic absorption of the material,the visible light transmittance of a single-layer VO₂ film is usually less than 40%,which will greatly increase the lighting energy consumption and reduce the energy saving efficiency.In order to improve the performance of VO₂ thin films and promote their commercial application,it is usually necessary to design VO₂ thin films into a composite phase structure or add an antireflection layer.In this thesis,the composite phase vanadium oxide thin films were prepared by rapid annealing process.On this basis,the influence mechanism of the HfO₂ antireflection layer on the optical properties of the composite phase vanadium oxide thin films was studied,and VORTA(Vanadium Oxide Rapid Thermal Anneal)/HfO₂ bilayer composite films with excellent performance were prepared.At the same time,the VO₂(M)/HfO₂ film with monoclinic vanadium oxide as the bottom layer was prepared by rapid annealing of VOx(amorphous)/HfO₂ double-layer film.The specific research contents are as follows:(1)The optical properties of VO₂(M)/HfO₂ and(V₂O₅/VO₂)/HfO₂ thin films were simulated by effective medium theory and transport matrix method.According to the simulation results of the variation of the transmission spectrum of the single-layer VO₂(M)film with the thickness,the thickness of the subsequent film was determined.For the VO₂(M)/HfO₂ structure,simulations of different thicknesses of HfO₂ were carried out,and the optimal thickness of the HfO₂ film was determined.For the V₂O₅/VO₂ composite structure,the transmission spectrum simulation of different volume fractions of VO₂ was carried out,and the optimal volume fraction of VO₂ was determined.For the(V₂O₅/VO₂)/HfO₂ structure,the thermochromic properties of HfO₂ films with different thicknesses were simulated,and the optimal thickness of the HfO₂ films was determined.(2)Referring to the above simulation results,VORTA/HfO₂ bilayer composite films were prepared by room temperature magnetron sputtering and rapid annealing process,and the microstructure analysis and transmission spectrum test of the samples were carried out.The material properties of VORTA did not change during the sputtering of the HfO₂ layer.The phase transition temperature of VORTA/HfO₂ is lower than that of conventional VO₂(M)films due to the strain effect in VORTA films.Compared with single-layer VORTA,VORTA/HfO₂ exhibits better optical performance(The visible light transmittance T_lum is 51.6%,and the solar spectrum modulation capability?T_sol is 15.4%).In accelerated aging experiments,VORTA/HfO₂ showed good environmental stability.(3)The VO₂(M)/HfO₂ film with monoclinic vanadium oxide as the bottom layer was prepared by rapid annealing of VOx/HfO₂ bilayer film.The modulation mechanism of the preparation process parameters(oxygen flow rate,rapid annealing time and temperature during magnetron sputtering of amorphous vanadium oxide films)on the microstructure of VO₂(M)/HfO₂ films was investigated.The optical properties of the bilayer films prepared under different conditions were evaluated.Compared with monolayer VO₂(M),VO₂(M)/HfO₂ films exhibits better optical properties(40.9%for T_lumand 17.7%for?T_sol).