THz spectroscopy of VO 2 epitaxial films: Controlling the anisotropic properties through strain engineering

Abstract

We use THz time-domain spectroscopy to investigate the farinfrared properties of vanadium dioxide thin films, strain-engineered through epitaxial growth on (100)R TiO 2 substrates. The films exhibit a large uniaxial tensile strain along the rutile c-axis. X-ray diffraction measurements reveal a structural transition temperature of 340 K, whereas independent THz conductivity measurements yield a metal-insulator transition temperature of 365K along c R. Analysis of these results suggests a Mott-Hubbard behavior along the c R-axis. Along c R the conductivity is approximately 5500 (Ω cm) -1, comparable to bulk single crystals. The tensile strain leads to remarkably uniform cracking oriented along the rutile c-axis, resulting in a large conductivity anisotropy in our single-crystal epitaxial thin films. We discuss our results in the context of previous measurements and calculations of the properties of VO 2, under different strain conditions. This work demonstrates the potential of strain engineering to tune the properties of complex materials while also serving as a powerful discriminatory tool for probing microscopic responses. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.