Vanadium dioxide (VO2) thin films were deposited at room temperature on Corning 2947 glass substrates by direct current (DC) magnetron sputtering with a high purity VO2 target. Crystal structure, surface topography, surface morphology and optical properties of the deposited VO2 thin films were investigated. The deposited films exhibited a single orientation of (110) with a crystallite size of 41.3 nm as confirmed by the X-ray diffraction analysis and Scherrer formula, respectively. From the surface topography analysis, the film surface had root mean square surface roughness of ~6.8 nm and consisted of round-shaped grains. Similarly, from the surface morphology analysis, spherical-like grains were observed on the surface of the deposited VO2 thin films with estimated average grain size of 34.2 nm. The deposited thin films showed high transmittance and low reflectance in the visible and near-infrared wavelength regions at room temperature. In addition, from the optical transmittance against temperature measurements, only a few transmittance variation and a slight change in hysteresis loop were detected during heating and cooling between room temperature and 100 °C. Hence, the deposited VO2 thin films were found to exhibit lack of phase transition.
Investigation on properties of vanadium dioxide (VO2) thin films has received significant attention as it is a thermochromic material potentially for applications on architectural glazing in order to reduce energy consumption from usage of air-conditioning system. Most studies have focused on the hysteresis behavior of thermochromic VO2 thin films that occurs at a certain phase transition temperature. Although large area coating techniques have recently been developed, there are still many obstacles in trying to deploy energy-efficient windows. Hence, this work concisely reviews on VO2 thin films as thermochromic materials, and developments on preparation methodologies in order to enhance the thermochromic characteristics of VO2 thin films.
Influences of substrate temperature on crystal structure, surface topography and surface morphology of cerium dioxide or ceria (CeO2) thin films deposited using radio frequency (RF) magnetron sputtering were studied. The substrate temperature was varied i.e. room temperature, 100, 200 and 300 °C. The characteristics of the film surface could be controlled by tuning the substrate temperature. As studied in the X-ray diffraction (XRD) analysis, the CeO2 thin films exhibited a cubic fluorite structure with predominant (200) orientation at substrate temperature of room temperature and 200 °C, while (111) preferred orientation at substrate temperature of 100 and 300 °C. The CeO2 films featured uniform surface topography and surface morphology, as observed from the atomic force microscopy and scanning electron microscopy analyses, respectively. The surface roughness and the average grain size of the films fluctuated with increasing substrate temperature. This phenomenon was suggested due to the difference in the preferential orientation of the films as in the XRD analysis.
Properties of vanadium dioxide or vanadia (VO2) thin films prepared using radio frequency (RF) magnetron sputtering with a pure VO2 target were analysed. The properties consisted of crystal structure, surface topography, surface morphology as well as optical and thermochromic properties of VO2 thin films. The deposition was conducted in an argon atmosphere of flow rate of 30 sccm, substrate temperature of 500 °C and RF sputtering power of 100 W. The film, which was deposited with film thickness of 50 nm, exhibited a single orientation of (110) orientation. The film surface featured quite homogeneous and continuous surface topography, and spherical-like grains that represented grains in VO2(M) phase. The film had low surface roughness resulting in quite high optical transmittance and relatively low optical reflectance, at room temperature throughout visible and near-infrared regions. Meanwhile, the film also showed a phase transition at ∼65.0 °C with hysteresis width of 38 °C.
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