Thermochromic properties of VO2 nano-coatings by inverted cylindrical magnetron sputtering
Madiba, Itani Given
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Vanadium dioxide (VO2) films have been known as the most feasible thermochromic nano-coatings for smart windows which self control the solar radiation and heat transfer for energy saving and comfort in houses and automotives. Such an attractive technological application is due to the fact that VO2 crystals exhibit a fast semiconductor-to-metal phase transition at a transition temperature TM of about 68°C, together with sharp optical changes from high transmitive to high reflective coatings in the IR spectral region. The phase transition has been associated to the nature of the microstructure, stoichiometry and some other surrounding parameters of the oxide. This study reports on the effect of the crystallographic quality controlled by the substrate temperature on the thermochromic properties of VO2 thin films synthesized by inverted cylindrical magnetron sputtering. Vanadium dioxide thin films were deposited on glass substrate, at various temperatures between 350 to 600 0C, deposition time kept constant at 1 hour. Prior the experiment, deposition conditions such as base pressure, oxygen pressure, rf power and target-substrate distance were carefully optimized for the quality of VO2 thin films. The reports results are based on AFM, XRD, RBS, ERDA and UV-VIS. The atomic force microscopy (AFM) was used to study the surface roughness of the thin films. Microstructures and orientation of grain size within the VO2 thin films were investigated by the use of X-ray diffraction technique. The stoichiometry and depth profiles of the films were all confirmed by RBS and ERDA respectively. The optical properties of VO2 were observed using the UV-Vis spectrophotometer.