Bidirectional tuning of phase transition properties in Pt : VO2 nanocomposite thin films

Abstract

A phase transition material, VO₂, with a semiconductor-to-metal transition (SMT) near 341 K (68 °C) has attracted significant research interest because of drastic changes in its electrical resistivity and optical dielectric properties. To address its application needs at specific temperatures, tunable SMT temperatures are highly desired. In this work, effective transition temperature (T_c) tuning of VO₂ has been demonstrated via a novel Pt : VO₂ nanocomposite design, i.e., uniform Pt nanoparticles (NPs) embedded in the VO₂ matrix. Interestingly, a bidirectional tuning has been achieved, i.e., the transition temperature can be systematically tuned to as low as 329.16 K or as high as 360.74 K, with the average diameter of Pt NPs increasing from 1.56 to 4.26 nm. Optical properties, including transmittance (T%) and dielectric permittivity (ε′) were all effectively tuned accordingly. All Pt : VO₂ nanocomposite thin films maintain reasonable SMT properties, i.e. sharp phase transition and narrow width of thermal hysteresis. The bidirectional T_c tuning is attributed to two factors: the reconstruction of the band structure at the Pt : VO₂ interface and the change of the Pt : VO₂ phase boundary density. This demonstration sheds light on phase transition tuning of VO₂ at both room temperature and high temperature, which provides a promising approach for VO₂-based novel electronics and photonics operating under specific temperatures.