Crystal Structure of Evaporated MgO Films on Amorphous and Polycrystalline Substrates

Abstract

Thin films of MgO were prepared by deposition from the vapor phase on amorphous and pylycrystalline substrates. Transmission and reflection electron diffraction were used to determine the orientation of the crystals in these MgO films. It was found that, on amorphous substrates initially at room temperature, the films possessed a crystal orientation which varied with film thickness. Films thinner than ∼ 500 Å showed a random orientation. As the film thickness was increased above ∼ 500 Å, a [111] preferred orientation was developed with an axis inclined away from the substrate normal and toward the direction of the vapor beam at oblique vapor incidence. At high substrate temperature (∼ 150–300 °C), the films followed the same behavior during growth. This preferred orientation is interpreted as a final growth orientation. On silver films as substrates, initially at room temperature, the same [111] preferred orientation was observed in films ≲ 100 Å thick and with increasing film thickness the orientation persisted. In thick deposits a slight inclination of the orientation axis was also observed at oblique vapor incidence. These results suggest that on Ag substrates the orientation is an initial nucleation orientation and also a final growth orientation.