Thermochromic VO2 film deposited on Al with tunable thermal emissivity for space applications

Thermochromic VO2 thin films were deposited on various substrates, namely quartz, Si, and Al, using RF reactive magnetron sputtering deposition. IR thermometry measurements reveal that the emissivity properties of the system VO2/substrate strongly depend on the IR optical properties of the substrate. VO2 films deposited on a highly IR reflective substrate such as Al, present an emissivity dependence on temperature that is opposite to that of VO2 deposited on an IR transparent substrate, like quartz and Si. XPS and Raman measurements show that VO2 undergoes a crystalline structure transition from monoclinic to tetragonal when deposited on Al, quartz, and Si. They also confirm that the transition is accompanied by a change from an insulator or semiconductor state to a metallic state. The emissivity performance of VO2/Al as compared to that of VO2/quartz and VO2/Si is attributed to the higher IR reflective properties of Al in comparison to quartz and Si. The increase of emissivity with temperature makes the VO2/Al system of strong interest as a passive smart radiator device for thermal control of spacecraft. (C) 2011 Elsevier B.V. All rights reserved.