Durability of thermochromic VO2 thin films under heating and humidity: Effect of Al oxide top coatings

•Thermochromic VO2 films were made by sputtering.•These films transformed to non-thermochromic V2O5 under heating and humidity.•Top coatings of Al oxide delayed the oxidation very significantly.

An explorative study was performed on sputter-deposited thermochromic (TC) VO2 films exposed to heat treatment under dry and humid conditions. The ambient conditions were harsh and 80-nm-thick VO2 films were rapidly converted to non-TC V2O5. It was found that a 30-nm-thick sputter-deposited Al oxide top coating provided good protection and delayed the oxidation for more than one day upon heating in dry air at 300 °C and that protection occurred for several days at 95% relative humidity and 60 °C. The thickness of the Al oxide was important and, expectedly, increased thickness yielded enhanced protection. Our results are important for TC fenestration as well as for other technical applications.