AVS 58th Annual International Symposium and Exhibition
    Thin Film Division Friday Sessions
       Session TF-FrM

Paper TF-FrM11
Crystallographic Orientation of Vanadium Dioxide Nano-Grains on Various Single-Crystal Sapphire Substrates

Friday, November 4, 2011, 11:40 am, Room 110

Session: Thin Films: Growth and Characterization II
Presenter: Felipe Rivera, Brigham Young University
Authors: F. Rivera, Brigham Young University
J. Nag, Vanderbilt University
R.F. Haglund Jr., Vanderbilt University
R. Davis, Brigham Young University
R. Vanfleet, Brigham Young University
Correspondent: Click to Email
Vanadium dioxide (VO2) is a material of particular interest due to the reversible semiconductor to metal phase transition that VO2 exhibits near room temperature (~ 68 °C) and the accompanied hysteresis. Recent studies suggest that external stresses applied to VO2 crystals have an effect on the transition temperature and hysteresis. Thin films of VO2 were deposited on three different cuts of sapphire by Pulsed Laser Deposition (PLD). Electron Back-Scattered Diffraction (EBSD) was used to study the orientation of the crystalline VO2 grains obtained and showed epitaxial relationships between the different single-crystal substrates. A predominant family of crystallographic relationships is present in all cuts of sapphire wherein the rutile VO2 {001} planes tend to lie parallel to the substrate's {10-10} and the rutile VO2 {100} planes lie parallel to the substrate's {1-210} and {0001}. This family accounts for the majority of the VO2 grains observed on all substrates with specific orientations (and stresses) depending upon the substrate's normal direction. Transmission Electron Diffraction patterns taken from cross-section of particles of the A and R cut sapphire substrates helped to lift the ambiguity present in the rutile {100} axes. EBSD showed additional families of relationships in the C and R cuts of sapphire, most related to the aforementioned predominant family. Variations in the transition temperatures of the deposited thin films mentioned in this study are attributed to the stresses generated by the epitaxial relationships.