Correlation of metal-to-insulator transition and strain state of VO2 thin films on TiO2 (110) substrates

Abstract

We explore the possibility of tuning the metal-to-insulator transition (MIT) of crystalline VO2 thin films by strain engineering. We deposit high-quality VO2 epitaxial films of different thicknesses on TiO2 (110) substrates by pulsed laser deposition. The strain state of the deposited film varies with its thickness. This allows us to correlate the MIT characteristics with the strain state of the VO2 film by a careful characterization of the structural and electrical properties. Thin VO2 films on TiO2 (110) substrates are almost fully strained up to thicknesses of about 20 nm and exhibit tensile strain along the c axis of the (high-temperature) metallic rutile phase leading to an increase in the MIT temperature by as much as 30 °C in comparison to the almost fully relaxed 300 nm-thick VO2 film. The strain gradient within the thicker samples leads to a continuous serial switching of layered regions of the VO2 film from the insulating to the metallic state with increasing temperature.