Abstract
A rhenium single crystal with an initial (0001) orientation, recrystallized by twinning to yield {101̄ n} planes parallel to the surface. The LEED pattern displayed a one-dimensional superstructure which could be attributed to a system of regularly spaced steps. The 00 beam is diffracted from the (0001) plateaus of the steps, and not the high index plane. Heating the crystal in oxygen apparently modified the step system. Residual gas analysis showed that even after a “clean” LEED pattern has been obtained, carbon contamination is removed from the surface as CO by heating the sample in oxygen. Electropolishing of Re (0001) may result in basal plane etching. The faces of the rhombohedral pyramids thus formed were determined by analysis of LEED patterns and photomicrographs to be {112̄ n}, n = 2, 3, 4. The facet reflections are shifted in energy with respect to the normal reflections, due to a difference in inner potential. Also a dynamic interaction between the two sets of beams is suggested by observations. An intensity versus voltage plot for the normal 00 beam exhibits “forbidden” Laue maxima out to the 21st order. The absence of all but two secondary Bragg peaks may be explained with an Ewald sphere construction.
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