Functional Thin Films for Glazing Application

Abstract

Vanadium dioxide is a thermochromic material with great potential for use in intelligent glazing. The thermochromic properties result from a metal to semiconductor transition (MST) where there is an associated structural change from the higher temperature rutile structure to the lower temperature monoclinic structure. This structural transition results in significant changes in optical properties and electrical conductivity. Various chemical vapour deposition (CVD) methodologies have been utilised, to produce thin films of vanadium dioxide. Different strategies are presented for the inclusion of metal dopants and the production of nano-composites. The use of a surfactant molecule, tetraoctyl ammonium bromide (TOAB), is discussed and shown to significantly alter the morphology and microstructure of the deposited films. It is further shown that these microstructural changes lead to an enhancement of thermochromic properties. Films were analysed by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Their optical and thermochromic behaviour was also determined. The effect of transition metal dopants leads to changes in the MST temperature; furthermore incorporation of gold nano-particles in the films leads to significant changes in the colour of the film due to the presence of a surface plasmon resonance band. Energy modelling studies were performed with data generated from these coatings and several standard glazing products to illucidate their usefulness in contemporary archetecture. It was found that transition temperature, colour and the thermochromic “switching” properties all play a part in the energy performance of these coatings.