ATOMIC STEP STRUCTURES ON CLEAVED ALPHA-ALUMINA (012) SURFACES

Cleaved a-alumina (012) surfaces are imaged with reflection electron microscopy (REM). A RHEED-THEED diffraction method is demonstrated for on-line determination of surface orientation. The observed defect structures on the (012) surface include vacancy-type of terraces, islands, kinks and ledges of a few atoms high, Steps of height possibly less than about 0.8 angstrom may be seen in REM images. The formation of the surface steps of different heights is described based on the atomic structure of the bulk crystal. The electron beam damage to the surface domains initially terminated with oxygen and aluminium layers, respectively. is interpreted based on the electrostatic desorption model after Auger decay. This effect is responsible for the bright-dark band-type contrast observed in REM images, and can be employed to identify the surface termination. It has been found that the REM image sensitivity is significantly improved with a field emission gun (FEG).