Defects in epitaxial insulating thin films

Abstract

Defects on thin epitaxial insulator films of NaCl(100), KCl(100), and MgO(100) generated during growth and by electron bombardment are investigated by high-resolution spot profile analysis in low-energy electron diffraction (SPALEED), photoelectron spectroscopy (XPS, UPS), electron energy-loss spectroscopy (EELS), and thermal desorption spectroscopy (TDS). All three insulators contain morphological defects: NaCl overgrows the monatomic Ge(100) steps in a carpet-like mode, whereas KCl grown on NaCl(100) forms a regular array of stacking faults up to three monolayers of KCl, and the MgO film grown on Ag(100) reveals a broadened (1 × 1) pattern in LEED due to the formation of mosaics. In EELS, surface colour centres, produced by electron bombardment, on NaCl induce losses at 2.1 eV for FS centres and at 1.5 eV for MS centres and on KCl induce losses at 1.6 eV and 1.0 eV, respectively. Close to room temperature, high electron exposures result in additional losses in the band gap due to surface and bulk plasmons of Na and K clusters. A similar anion vacancy defect structure on MgO with losses at 2.1 eV and 3.3 eV can be produced by incomplete desorption of metallic Mg from the MgO(100) surface. TDS experiments show that colour centres increase the binding energy of Kr physisorbed on NaCl(100) by about 25%. The concentration of point defects was determined by titration with noble gases in thermal desorption.