2025/07/31 by H. Acosta-Rivera, Víctor Rico, Acosta-Rivera, H. +13
Engineering · Materials Science · #Applied Physics (physics.app-ph) #FOS: Physical sciences #Ga2O3 and related materials #Gas Sensing Nanomaterials and Sensors #Materials Science (cond-mat.mtrl-sci) #Transition Metal Oxide Nanomaterials
paper · pdf · doi:10.48550/arxiv.2507.23393
openalex publication_date 2025/07/31 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The formation of VO2 crystalline domains in amorphous substoichiometric nanocolumnar VOx thin films subjected to an oxidation process at temperatures below 300°C has been studied. It is obtained that values of [O]/[V] above 1.9 lead to the sole formation of V2O5 after oxidation, while values below 1.9 favor the formation of VO2, V3O7 and V2O5 crystalline domains for temperatures as low as 260°C. Moreover, it is found that the adsorption of oxygen and its incorporation into the film network produce a relevant volume expansion in a so-called swelling mechanism that makes pores shrink. Under some specific conditions, the low temperature oxidation does not only trigger the formation of VO2 domains but also a drastic reduction of oxygen-deficient amorphous VOx in the films, which clearly improves the overall transparency and thermochromic modulation capabilities. The changes in the optical and electrical properties of these films during the metal-insulator transition have been studied, finding the best performance when the stoichiometry of the film before oxidation is [O]/[V]=1.5 and the oxidation temperature 280°C. These conditions yield a relatively transparent coating that presents an optical modulation in the near-infrared range of nearly 50% and a drop of electrical resistivity of more than two orders of magnitude. A tentative model based on the volume increase experienced by film upon oxidation is proposed to link the structural/chemical features of the films and the formation of VO2 domains at such relatively low temperatures.