Study On Preparation And Properties Of W-doped VO₂ Films

Vanadium dioxide (VO2) exhibits thermochromism via a reversible metal-to-semiconductor phase transition(MSPT) around 68℃, accompanied by dramatic changes in electrical resistivity and optical properties. The transition temperature Tc of VO2 films can be reduced to room temperature by doping. Doped VO2 films are promising materials for its properties of phase transition.W-doped VO2(V1-xWxO2)films were deposited onto glass substrates by reactive magnetron sputtering and vacuum annealing. The composition ,micro-structure, morphology and thickness of the films were characterized by XPS, XRD, SEM, AFM and step profiler. Thermal hysteresis loops of resistance were measured by four-point probe method.The composition,micro-structure, morphology and transition characteristics of VO2 films prepared under various parameters were discussed. The results showed that: as the m(O2)/m(Ar) ratio decreased in preparing vanadium oxide films by reactive sputtering, the mean valence of V in the films decreased, and the films changed from V2O5 phase into mixed-phase of low valance vanadium oxides. While the m(O2)/m(Ar) ratio was 1:11, the main component of films was V2O5. As time rose in deoxidizing V2O5 films by vacuum annealing, the films underwent a V2O5→V6O13→mixed-phase of VO2(B),VO2(γ)and V6O13→mixed-phase of VO2(A)and V6O13 transition, the grains in the films became bigger, and the crystalline was improved gradually. The VO2 films, which undergoing MSPT around 62℃, accompanied by a resistivity variation as large as 2.1 decades and a obvious thermal hysteresis of 10℃, was ahieved.The influences of tungsten doping on transition properties of V1-xWxO2 films were analyzed. The results showed that: tungsten existed as W6+and W5+ in V1-xWxO2 films. Tungsten (0