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

A phase transition material, VO, 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) tuning of VO has been demonstrated via a novel Pt : VO nanocomposite design, i.e., uniform Pt nanoparticles (NPs) embedded in the VO 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 : VO nanocomposite thin films maintain reasonable SMT properties, i.e. sharp phase transition and narrow width of thermal hysteresis. The bidirectional T tuning is attributed to two factors: the reconstruction of the band structure at the Pt : VO interface and the change of the Pt : VO phase boundary density. This demonstration sheds light on phase transition tuning of VO at both room temperature and high temperature, which provides a promising approach for VO-based novel electronics and photonics operating under specific temperatures.