Diffraction patterns obtained from atomically clean germanium surfaces contained half-integral order beams in (110) azimuths for both the (100) and (110) surfaces and in all azimuths for the (111) surface. These results were considered to be due to displacements of the surface atoms from their normal bulk lattice positions in the surface plane. Adsorption of oxygen on all of these surfaces extinguished all of the diffraction beams which were not of integral order. In addition to the normal surface lattice spacings of clean (111) and (100) surfaces of silicon, there were surface structures with larger spacings, most of which depended upon the conditions of ion bombardment and/or subsequent heat treatment. Two such structures were observed for the (100) surface of silicon. One was a double-spaced lattice in the (110) azimuth; similar to that for germanium. The other had a spacing which was about 8% greater than that of normal silicon, and was obtained only after radiation quenching of the crystal from 1000C. Two large-spaced structures were observed for the (111) surface. All of these structures were extinguished by exposure to oxygen. Evidence was presented which indicated that these structures were not due to contamination, but  to the silicon itself.

Structure and Adsorption Characteristics of Clean Surfaces of Germanium and Silicon. R.E.Schlier, H.E.Farnsworth: Journal of Chemical Physics, 1959, 30, 917