OBSERVATION OF SURFACE CRYSTALLOGRAPHY BY REFLECTION ELECTRON-MICROSCOPY

Surface crystallography of (111) and (100) facets on spherical single crystals of Pt and Au was studied by reflection electron microscopy. Effects of surface channelling allow a very accurate determination of crystallographic directions. The facets were cleaned by Ar ion bombardment and smoothened by electron beam heating. In order to obtain atomically flat surfaces the specimens had to be cooled down very slowly after annealing. By such treatments the (100) surfaces of Au and Pt and also the (111) surface of Au are reconstructed with certainty. The direct electron microscopic observation of these reconstructions is very difficult or impossible after the transfer through the atmosphere to a conventional electron microscope. However, modifications of the surface topography controlled by the reconstruction can be observed. As an example the edges of the (100) facets at the starting curvature of the crystal sphere are shown. Here sequences of monatomic steps are formed, following the directions of the (100) surface reconstruction, which is written in matrix form as N 1 -1 5 with N = 12-14. Reconstructed domains on (100) surfaces of Pt and Au could be imaged. As another example for surface crystallography the observation of screw dislocations starting a monatomic step and edge dislocations forming a low-angle grain boundary are shown. © 1990.