Vanadium dioxide based thin films: enhanced performance for smart window applications
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Date
2010
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Publisher
University of Dar es Salaam
Abstract
Thermochromic vanadium dioxide (VO2) thin films that can control near infrared radiation throughput across a window were studied. Through precise control of the deposition conditions, single phase stoichiometric VO2 films were fabricated. A study on the influence of film thickness on the properties of VO2 films provided the optimum film thickness for a good compromise between thermochromism and luminous transmittance, Tlum. Multilayer stacks that significantly improved Tlum and solar modulation or those showing angular sensitivity were designed, employing VO2 optical constants extracted from transmittance and reflectance data. Particularly the three layer stack comprising of one VO2 layer between two antireflection layers, AR/VO2/AR, provided strong Tlum enhancement with calculated Tlum of ~59% compared to ~ 39 % for single layer VO2 film. Data from the multilayer calculations were employed in the fabrications of the respective multilayer structures. The optimum three layer structure gave a strikingly high value of Tlum, of 62.8 % in the semiconductor phase. Improvement in solar modulation was achieved by the five layer structures. The structures also displayed moderate angular sensitivities. Doped VO2 films were studied with a view to improving luminous transmittance and reducing the transition temperature of the films. A particularly important finding was the magnesium doped VO2 films, which resulted into a combined effect of significantly increasing the Tlum and reducing c, both of which are highly desired if the films are to be used for smart window applications. Aluminum doping showed significant improvement in Tlum but had c values higher than those of undoped films where as tungsten doping resulted into reduced transition temperature.
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Keywords
Thin films, Coatings, Vanadium dioxide
Citation
Mlyuka, N.R (2010) Vanadium dioxide based thin films: enhanced performance for smart window applications. Ph.D dissertation, University of Dar es Salaam. Available at http://41.86.178.3/internetserver3.1.2/detail.aspx?parentpriref=