AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS1+MC-WeA

Paper SS1+MC-WeA6
Surface Defects on MgO Thin Films: Formation, Detection, Electronic and Chemical Properties

Wednesday, October 4, 2000, 3:40 pm, Room 208

Session: Oxide Surfaces, Interfaces and Defects
Presenter: A.A. Kolmakov, Texas A&M University
Authors: A.A. Kolmakov, Texas A&M University
X. Lai, Texas A&M University
J.A. Stultz, Texas A&M University
D.W. Goodman, Texas A&M University
Correspondent: Click to Email
Surface defects play a significant role on metal oxide surfaces since they determine its electronic structure, chemical reactivity and adsorbate kinetics. There is great interest in studying surface defects on thin-film metal oxides to understand the properties of supported catalysts and gas sensing devices at the molecular level. Because of the low density of these oxide defects and sample charging, experimental studies of oxide surface defects still remain a challenging task. Using an ultrathin film deposition methodology and high surface sensitive capabilities of metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS) and temperature programmed desorption (TPD) along with scanning tunneling microscopy (STM), the properties of surface and near-surface defects were probed. A comparative study of morphology and electronic structure with reactivity of low-defect MgO(100) films was undertaken. Defect-ridden films exhibited occupied levels located ~2 eV above the top of the valence band, observed as a separate band in MIES, unlike defect-free thin films. This additional feature was attributed to the emission of electrons from point defects (F-centers) created on the surface and subsurface regions. Initially unseen in MIES, extended defects became detectable via NO titration. These defects manifest themselves as strong, reactive centers. MIES and TPD data indicate that at ~100 K, NO adsorbs dissociatively on surface defects and produces N@sub 2@O. Differences in electronic and chemical properties between these two films were further evidenced from their morphological differences as observed by STM.