Epitaxy of MgO on alkali halides with NaCl-type structure

Abstract

Reflection high-energy electron diffraction has been used to examine the growth of MgO on (001) surfaces of LiF, NaCl, and KCl in the temperature range 25–250 °C. MgO grew initially with parallel orientation, i.e., (001)MgO∥ (001)s and [100]MgO∥[100]s. The substrate temperature at which parallel orientation occurred depended on the nature of the substrate, increasing in the sequence LiF, NaCl, and KCl. The mode of MgO growth did not depend on the substrate temperature and the lattice misfit. MgO initially formed three-dimensional nuclei. At high substrate temperatures (250 °C) the range of film thickness over which parallel orientation persisted depended on the nature of the substrate, decreasing in the sequence LiF, NaCl, and KCl. For a given substrate this range of film thickness increased with increasing substrate temperature. Infrared spectra obtained for films deposited on substrates at 25–250 °C showed the presence of hydroxyl groups only in films deposited on substrates at low temperatures (25 °C). These results suggest that (1) the range of film thickness over which parallel orientation persists is influenced by the misfit between the MgO and the substrate lattice, decreasing with increasing lattice misfit and (2) the parallel orientation is also influenced by the incorporation of impurities such as hydroxyl groups into the growing film at later stages of growth on substrates at low temperatures.