Microstructural Investigations of VO[sub.2] Thermochromic Thin Films Grown by Pulsed Laser Deposition for Smart Windows Applications

The structural properties of VO[sub.2] thin films, grown on either LSAT or Si substrates by pulsed laser deposition (PLD), are elucidated by means of transmission electron microscopy (TEM) methods. The TEM observations confirmed the successful growth of VO[sub.2] by PLD in variable thicknesses, by optimizing the O[sub.2] partial pressure and growth temperature. The films adopt a columnar polycrystalline morphology with narrow columns, up to the film thickness height. Four VO[sub.2] polymorphs have been detected by electron diffraction and high-resolution TEM (HRTEM) analysis, with M1 being by far the most abundant phase. Post-experimental strain measurements in HRTEM images have revealed that the actual residual strain is minimized due to the columnar morphology of the VO[sub.2] grains, as well as intrinsic oxide layers in the VO[sub.2] /Si epitaxy. The TEM outcomes confirmed the complementary electrical and magnetic measurements in the films, where a transition from a monoclinic M1 to a rutile VO[sub.2] R phase has been identified, influenced by the initial percentage of phases in thick VO[sub.2] films.