Work

Thermochromic properties and surface chemical states of reactive magnetron sputtered vanadium oxide thin films at various deposition pressures

Year: 2024

Type: article

Abstract: Vanadium oxide thin films were prepared using reactive magnetron sputtering method, varying the deposition pressures from 4 to 10 mTorr while maintaining the other sputtering parameters constant. Our investigations revealed sensitive dependence of deposition pressure, chemical states of the V and O atoms, crystal phases, and thermochromic (TC) optical modulation. Specifically, the film deposited at 8 mTorr displayed distinct TC characteristics with a prevalent monoclinic m-VO 2 phase according to X-ray diffraction (XRD), supported by X-ray photoelectron spectroscopy (XPS). Optical transmittance modulation and electrical property measurements revealed a metal–insulator transition (MIT), confirming the intimate connection between TC characteristics and presence of the m-VO 2 phase. Films deposited at pressures lower or higher than 8 mTorr exhibited typical semiconductor behavior without TC characteristics, further supported by in situ XRD, where (110) plane shifted to lower angle upon heating above τ C . Chemical state analysis by XPS revealed a clear correlation between V−O peaks and the presence of a VO 2 phase, with the film deposited at 8 mTorr displaying relatively large peak fitted area indicative of the VO 2 phase. These findings highlight the critical and sensitive dependence of the deposition conditions in tailoring the properties of vanadium oxide thin films and provide valuable insights for potential applications in chromogenic films. • Sputtered VO 2 film with an exceptionally narrow phase transition was deposited. • Deposition pressure varied to observe TC characteristic while fixing other parameters. • MIT phase transition directly observed with in-situ XRD and XPS analysis. • Crystallinity and chemical composition heavily depend on deposition pressures.

Source: Vacuum

DOI: 10.1016/j.vacuum.2024.113679