The Characterization of the Low-Index α-Al203 Surfaces by REM

Four low-index surfaces; (A-surface), (0001) (basal surface), (R-surface), and of the α-Al203 single crystals were investigated by reflection electron microscopy (REM) and reflection high energy electron diffraction (RHEED) techniques[1] and the characteristics of these surfaces are reported. Specimens were prepared by polishing and annealing[2, 3], Orientation of each surface was confirmed with x-ray diffraction using a Laue camera. Microscopy observation was carried out on a JEOL JEM-200CX TEM operated at 100 KV.To facilitate a fair comparison, the surface areas which were obviously affected by a macroscopic tilt, localized contamination, etc., were avoided. Only the flat, clean, and smooth areas were compared. The surface (Fig. 1. The scale in this figure also applies to all other figures.) shows large atomically flat areas divided by steps running in <000 1> and directions. The steps in this image are not of the same height. Some are one or two atoms high and others are much higher. Fig. 2 shows the surface which is periodically facetted. One type of the facets is flat and atomically smooth while the other type is rough. The (0001) planes display curved and/or straight steps[4]. An example of curved step configuration is shown in Fig. 3. Most of the steps in this image have the same height. This step configuration is similar to the surface shown in Fig. 4. However, the contrast of the steps are very different; on the (0001) surfaces the steps are much darker and well-defined. A summary of these four surfaces is presented in the table below.