Effects of ALUMINIUM AND TUNGSTEN CO-DOPINGON the electrical and optical properties of vo2 based thin films

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University of Dar Es Salaam
Vanadium dioxide (VO2) has been identified by many studies as a potential material for energy efficient window coatings. It is desirable to lower the transition temperature, c to the vicinity of room temperature and provide high luminous transmittance (Tlum). However, small magnitudes of luminous transmittance of doped VO2 thin films have still been the challenge for window applications of the VO2-based coatings. This study focused on determination of the effects of aluminium and tungsten co-doping on the electrical and optical properties of vanadium dioxide (VO2) based thin films with a view of combining both increasing luminous transmittance (Tlum) and lowering of the transition temperature (τc). The films were prepared by DC reactive magnetron sputtering. Targets of vanadium, vanadium and tungsten alloy (V 99 % - W 1 %) and vanadium and tungsten alloy stacked with aluminium pellets (V : W : Al) in a mixture of argon and oxygen gases were used. The films were deposited at 450 oC. Sheet resistances of the films were obtained using a two-point probe and the JANDEL multipurpose four point probe with RM3-AR test unit. Shimadzu SolidSpec-3700 DUV UV-VIS-NIR and Perkin Elmer Spectrum BX FT-IR spectrophotometers were used to investigate the optical properties of the films. The phase transition temperature was obtained from both the transmittance-vs-temperature and sheet resistance-vs-temperature curves. The results revealed that VO2 : W : Al2 thin films has enhanced the luminous transmittance to 54.2 % and reduced the transition temperature to 61 oC compared to 44.8 % and 68 oC respectively, for VO2 thin film alone. A change in sheet resistance of 2 orders of magnitude was recorded for both undoped and co-doped VO2 thin films.
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John, C(2013)Effects of ALUMINIUM AND TUNGSTEN CO-DOPINGON the electrical and optical properties of vo2 based thin filmsMaster dissertation, University of Dar es Salaam, Dar es Salaam