A HIGH-RESOLUTION ELECTRON-MICROSCOPY STUDY OF MGO/AL2O3 INTERFACES AND MGAL2O4 SPINEL FORMATION

MgO films were deposited on the (0110BAR)Al2O3 prism plane and the (0001)Al2O3 basal plane of sapphire by molecular beam epitaxy (MBE). Cross-sectional specimens with thicknesses of less than 15 nm were prepared so that the MgO/Al2O3 interface could be investigated by high resolution electron microscopy (HREM). Two different orientation relationships were obtained for MgO films deposited on the differently oriented sapphire substrates. Misfit dislocations at the interface were analysed and a structural model for the atomic arrangement of the interface was proposed. Good matches between simulated and observed images of the MgO/Al2O3 interfaces were obtained. The HREM observations, image simulations and optical diffractograms confirm that MgAl2O4 (spinel) forms at the interface by a solid state reaction under electron beam irradiation.