Atomic and Electronic Structure of Low-Index Surfaces

Silicon and germanium are the most important elemental semiconductors. They have the diamond cubic structure with sp hybrid bonds. The structure of the low index crystallographic planes, the only ones to be considered here, is shown in Fig. 1. It is seen that in the ill surfaces the atoms are triply bonded to the layer below and thus have one unpaired electron (dangling bond). Each atom of the 110 surfaces also... 

It is clear, then, that the surface atoms in Pt crystallites in the size range < 3nm have complex electronic and geometric structures which generate significant variations in reactivity between sites on Miller indices of low and high index, with dramatic potential in catalysis. 

By ion microscopy, the processes occurring on low index planes can be readily detected, whereas these are usually obscured by the high work function of these planes when observations are attempted by field emission of electrons. The ability of the ion microscope to reveal individual atoms, both in the adsorbed layer as well as in the substrate, opens up entirely new possibilities in the study of surfaces. This increase in resolution should permit a most detailed assessment of the relation between structure and surface processes. 

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