ABSTRACT
Vanadium dioxide (VO2) undergoes a thermally-driven semiconductor-to-metal phase transition near 67°C, transforming from a monoclinic to tetragonal structure, and accompanied by dramatic changes in electrical and optical properties. The change in the resistivity for single crystal material is precipitous, generally resulting in cracking of the sample; whereas polycrystalline thin films exhibit hysteresis when cycled through the phase transition. Studies of the range of homogeneity of VOx sintered powdered samples indicate that oxygen vacanies strongly influence the semiconducting-state properties of VO2 , but have much less impact on the metal phase. Presumably the formation of V interstitials results in a rise in the mobile electron concentration and a reduction in the overall conductivity change through the phase transition. Considerable attention has been given to modifying the phase transition properties of this material by a variety of means. It has been demonstrated that momentum transfer to film atoms by energetic ion bombardment during film growth can alter the microstructure, and thereby the properties, of thin films.
