Thermally generated defects in ultrathin MgO films on Mo(100) have been investigated using high-resolution electron-energy-loss spectroscopy (HREELS) in the 0–9-eV spectral region. The results indicate that the MgO films are thermally stable and nearly free from defects up to a temperature of 1100 K, above which defects in MgO are generated. The three distinct loss features observed at 1.15, 3.58, and 5.33 eV are due to electronic transitions associated with surface F centers, F aggregates, and F (or ${\mathrm{F}}^{+}$) centers, respectively. The addition of lithium into the MgO films produces [${\mathrm{Li}}^{+}$${\mathrm{O}}^{\mathrm{-}}$] centers and promotes the production of F-type defects upon high-temperature treatment. The formation of the [${\mathrm{Li}}^{+}$${\mathrm{O}}^{+}$] centers is likely a consequence of the substitution of ${\mathrm{Li}}^{+}$ for ${\mathrm{Mg}}^{2+}$ in the magnesium oxide lattice. The present studies have demonstrated the capabilities of HREELS for studies of electronic transitions associated with a variety of defects in the near surface region.

• Received 13 May 1992

DOI:https://doi.org/10.1103/PhysRevB.46.12688