Tunable insulator–metal transition in VO2-based nanocomposite thin films via strain and defect engineering

Vanadium dioxide (VO2), an insulator-to-metal material, has garnered significant research interest due to its potential applications in radiative coolers, optical memories, and optical switches. VO2 exhibits reversible metal-to-insulator transition near 68 °C, thereby requiring tunable transition temperatures (Tc) in VO2 thin films for practical device applications. In this work, we explore the role of strain, oxygen vacancies, and band bending in controlling the Tc in VO2 nanocomposite thin films deposited on c-cut sapphire by embedding different metallic nanoparticles in a VO2 nanocomposite thin film (Au, Ni, and W). All the VO2 nanocomposite thin films showed reduced switching, enlarged hysteresis width, and reduced Tc compared to pristine VO2 thin films grown on (0006) sapphire at similar deposition parameters, with W–VO2 thin films exhibiting the least Tc (49.6 °C). The reduced transition temperatures were found to be correlated with increased b axis strain, reduced work function of the VO2 thin film, and increased oxygen vacancy formation. Our study provides critical insights into the interplay between strain, band bending, and oxygen vacancies brought about by metallic nanoparticles in determining the structural and electrical properties of VO2 and thereby tuning Tc.