Structual Design, Optical And Electrical Performance Evaluation In Vanadium Dioxide Composite Films

Recently,researches on the thermochromic smart optical modulating ability of VO₂ and other vanadium oxide keep growing.The obstacles of single layer VO₂ on synthesis process,application performance and mechanism have been gradually being solved.Nevertheless,efforts are still demanded to improve the performance.In this paper,we solve the problem of high magnetron sputtering temperature,balance the sufficiently large transmittance with satisfied thermochromism and high mid-infrared reflectivity,creature a novel one-step annealing method to get self-assembly sturcture,and explore the thermochromic performance of some low-temperature transistion materials.Specifically,the main contents and results are as follows:1.By inducing ZnO seed layer and TiO₂ buffer layer,we got the VO₂/TiO₂/ZnO composit structure,lowing the deposition temperature from>400 ^oC to 300 ^oC in magnetron sputtering process.Compared with single VO₂,the VO₂/TiO₂/ZnO structure could also largely improve the luminous transmittance(T_lum)and solar modulating ability(?T_sol)of 26.5%in T_lum?20 ^oC?,12.4%in T_lum?90 ^oC?and 104.5%in?T_sol.Further work we applied V₂O₃ as both seed layer and buffer layer,and then got the VO₂/V₂O₃ structure,and then lowing the deposition temperature to 250 ^oC.2.The smart window structure has been designed integrally.Firstly the SiO₂?100nm?/AZO?300nm?/Glass was designed as the optimized Mid-infrared reflecting layer.Secondly the TiO₂?240nm?/VO₂?70nm?/TiO₂?10nm?/Glass structure was designed as solar modulating layer under the philosophy of skin comfort design.Finally this two multilayered stacks were combined together for energy efficient fenestration,the optical performance was measured as 42.5%in T_lum?25 ^oC?,39.8%in T_lum?95 ^oC?,6.9%in?T_sol,and the mid-infrared reflectivity was>80%,superior to existing literature.3.Composite films of VO₂-TiO₂ with self-assembled well-ordered multilayer structure were fabricated via a spinodal decomposition mechanism,which provided a facile and novel approach to fabricate nano-scale structures.We created a two-step approach,i.e.,the room temperature magnetron sputtering–annealing approach,to improve both the synthetic process and the product quality.We took advantage of different sapphire substrate planes?A-plane,R-plane,C-plane,and M-plane?to achieve different decomposition modes.We identified key mechanism into diffusion model with disorder-order transition.And we have found that the derived films exhibit superior optical modulation upon phase transition,significantly reduced transition temperature and hysteresis loop width,and high degradation resistance.4.Low-temperature thermochromic thin films of VO₂?B?and V₂O₃ have been fabricated and characterized.We deposited high quality epitaxial VO₂?B?thin films on STO?100?substrates,measured the optical properties variation among cooling and heating.The transition temperature was measured as 215K and the hysteresis loop width of 37K,the modulating ability reached up to 22.5%at the wavelegth of 2000nm.We grown epitaxial V₂O₃ thin films on sapphire as well as polycrystalline V₂O₃ films on glass or Si substrates,measured the optical modulation of 16%²5%with the various thickness of 30¹50nm at 2000nm.Meanwhile,we also optimized electrical performance of V₂O₃/SiN_x/Si samples by W-Ti co-doping.The obtained co-doped V₂O₃film shows a relatively high temperature coefficient resistant of-8.1%/K at 80K without hysteresis loop,which exhibits great potential in high sensitivity thermal resistor devices.Our work provides a comprehensive scenario of the V₂O₃ thin film physics.