A VO2 film exposed to ambient air is prone to oxidation, which will degrade its thermochromic properties. In this work, the authors deposited an ultrathin Al2O3 film with atomic layer deposition (ALD) to protect the underlying VO2 film from degradation, and then studied the morphology and crystalline structure of the films. To assess the protectiveness of the Al2O3 capping layer, the authors performed a heating test and a damp heating test. An ultrathin 5-nm-thick ALD Al2O3 film was sufficient to protect the underlying VO2 film heated at 350 degrees C. However, in a humid environment at prolonged durations, a thicker ALD Al2O3 film (15 nm) was required to protect the VO2. The authors also deposited and studied a TiO2/Al2O3 bilayer, which significantly improved the protectiveness of the Al2O3 film in a humid environment. (C) 2015 American Vacuum Society.