Study On Preparation And Properties Of Ag/VO₂ Composite Film

Vanadium dioxide?VO₂?thin film undergoes a metal-semiconductor reversible phase transition at⁶8?,and accompanys by a remarkable change in its light and electricity properties,leading to the wide application in the photovoltaic devices and smart windows.Aimed at the main factors restricting the application of VO₂ in photoelectric devices and smart Windows:relatively high room temperature phase transition temperature?T_c?,low solar modulation efficiency(?T_sol),and undesirable brownish yellow,the Ag nanoperiodic arrays?Ag PPAs?are controllably embedded in VO₂ films in this paper.By utilizing the local surface plasmon resonance characteristics?LSPR?of Ag PPAs with different micro-nano structures and different sizes,the inherent brownish yellow of the VO₂ film was diluted,and the controllable optical properties of composite films is achieved,further.At the same time,with the introduction of different amounts of metallic Ag PPAs,gradually reduce the phase transition temperature of VO₂.In this work,Ag PPAs of different sizes were prepared on a silicon?Si?and quartz substrate?SiO₂?via a polystyrene?PS?template method,and then compounded with a monoclinic VO₂ film with good crystal quality.By adjusting the size of Ag PPAs in VO₂ films,the optical/electrical properties of composite films were studied.From the resistivity-temperature??-T?curve,as the increase of specific surface area for the Ag nanoparticle in the composite film,the T_c is decreased.Combined with the analysis of its band model,with increase of the specific surface area of the Ag nanoparticle,more free electrons of the Ag nanoparticle would be injected into the VO₂ film,which results that the more absorbed energy at the nano-metal-semiconductor junction,leading to induced phase transitions at lower temperatures.From the absorption spectrum of the sample on the Si substrate,as the volume of the Ag nanoparticles decreases,the LSPR absorption peak undergoes a blue shift,diluting the brownish yellow inherent of the film.From the transmission spectrum of the sample on the SiO₂ substrate,as the decreased volume of the embedded Ag nanoparticles,the?T_sol of thin film increased from 17.26%to 27.86%.To get a series of PS templates with different specifications were obtained,plasma beam etching was introrduced to change the size and spacing of the PS spheres for the PS templates.Based on this,different sizes of Ag nanonets?Ag NNS?were successfully embedded into the VO₂ film by electron beam evaporation to fabricate Ag NNS/VO₂/SiO₂composite films,and the optical/electrical properties of the composite films were studied.From the?-T curves of the composite,as the increase of the embedded Ag NNS volume percentage,the T_c of film was decreased.Based on the transmission spectrum before and after the film phase transition,the volume percentage of the embedded Ag NNS in the composite film increases from 4.45%to 24.07%,and the?T_sol of samples decreases from26.56%to 13.20%.Therefore,the embedded Ag periodic arrays with special micro-nano structures can effectively tuned the optical-electrical properties of VO₂ films.