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A thin film of thermochromic VO2 was prepared on m-Al2O3 substrate using a radio frequency (RF) magnetron sputtering technique. The epitaxial growth of the monoclinic M1 phase of VO2 on the m-Al2O3 substrate was confirmed through synchrotron X-ray diffraction (XRD) measurements. The transformation of this monoclinic M1 phase into a rutile phase at ~68 °C was reflected in the temperature-dependent XRD measurements of the VO2 thin film. The temperature-dependent electrical resistance measurements of this sample also revealed an abrupt metal-to-insulator transition at ~68 °C, which is reversible in nature. Temperature-dependent X-ray absorption (XAS) measurements at V L-edge and O K-edge were performed to study the electronic structure of the epitaxial VO2/m-Al2O3 thin film during the metal-to-insulator (MIT) transition. [ABSTRACT FROM AUTHOR]

• N+ ion implantation induced modifications in the VO 2 films were studied. • N+ ion implantation has resulted in downward shift in structural transition temperature. • VO 2 film with implantation dose of 1 × 1015 ions/cm2 N+ ions showed metal to insulator transition at room temperature. Modifications in the structural and electronic properties of VO 2 films induced by N+ ion implantation were investigated. VO 2 films prepared by radio frequency (RF) magnetron sputtering deposition on quartz substrate were subjected to the N+ ion beam with 55 keV at different fluences (1 × 1015 and 1 × 1016 ions/cm2). Compared with the pristine VO 2 film (Tc ∼ 342 K), structural and electrical phase transition temperatures were shifted around room temperature in the N+ ion implanted sample (fluence = 1 × 1015 ions/cm2). Furthermore, a higher fluence of N+ ions (fluence = 1 × 1016 ions/cm2) had significantly modified the crystalline structure of VO 2 thin film, and a metallic behaviour was clearly noticed in the entire temperature range between 240 K and 373 K under this study. N+ ion implantation effectively induces the changes in the electronic structure of VO 2 thin films, which are further confirmed by the X-ray absorption spectroscopy (XAS) measurements. [ABSTRACT FROM AUTHOR]

• Structural phase transition in VO 2 thin films is modulated by annealing temperature. • Increasing annealing temperature led to increase in spectral weight of V 3 d || states. • Intermediate M2 phase is emerged in VO 2 films annealed at higher temperature (T > 510 °C). • Infrared (IR) switching temperature and IR switching performance is tailored by varying the annealing temperature. Monoclinic M1 to rutile structural phase transition (SPT) in thermochromic VO 2 is accompanied by the insulator to metal transition and transition from an infrared (IR) transparent to IR opaque phase. Fine control over the phase stabilization and the functional properties without additional doping can offer the ability to tailor VO 2 thin films for their respective applications. In this work, post deposition thermal annealing was used to control the phase stabilization and the modulation in thermochromic performance of polycrystalline VO 2 thin films. Monoclinic M1 to rutile SPT in VO 2 thin films was tracked by in-situ temperature dependent synchrotron X-ray diffraction measurements and an increase in the SPT temperature was observed with increasing annealing temperature. Intermediate monoclinic M2 phase emerges near the SPT temperature at higher annealing temperature. Temperature dependent X-ray absorption spectroscopy (XAS) measurements revealed the higher electron correlation effect among the V 3 d || states across the phase transition in VO 2 thin film having the intermediate phase. Spectral weight of V 3 d || states was found to increase with the annealing temperature. Lower annealing temperature drives the IR switching temperature towards room temperature while the higher annealing temperature improves the IR switching performance of VO 2 thin films. [ABSTRACT FROM AUTHOR]

Vanadium dioxide (VO 2) is one kind of desired thermochromic material for many smart devices because of its notable temperature-responsive infrared modulation and metal−insulator transition with underlying structural phase transition (SPT). Understanding on the tuning of these properties in an anticipated manner is essential to accomplish device realization. Here, we report the annealing time induced modifications in SPT and the thermochromic properties of VO 2 thin films. Using RF sputtering deposition, VO 2 thin films were grown at room temperature and their ex-situ annealing was carried out at 600 °C for different time from 2 min to 60 min. Structural, electronic and thermochromic properties of these films were investigated. VO 2 thin films samples annealed for longer time exhibit larger crystallite size, higher surface roughness and SPT temperature, and the reduced hysteresis width of SPT during heating and cooling cycle. X-ray absorption spectroscopy results indicate that the variation in the annealing time do not alter the electronic structure significantly. Nevertheless, VO 2 thin film samples with prolonged annealing display higher IR transmittance modulation across the SPT. • VO 2 thin films were stabilized by giving post deposition annealing treatment to room temperature deposited films. • Variation in annealing time modifies the structural phase transition of VO 2 thin films. • Thermochromic properties of VO 2 thin films were tailored by controlling the annealing time. [ABSTRACT FROM AUTHOR]