HEXAGONAL AND NONHEXAGONAL SUPERLATTICE STRUCTURES ON STAGE-1 ALKALI-METAL GRAPHITE-INTERCALATION COMPOUNDS STUDIED BY SCANNING TUNNELING MICROSCOPY

We have investigated the surface of stage-1 C8M (MCs, Rb) graphite intercalation compounds by scanning tunnelling microscopy in an inert gas atmosphere. On the atomic scale we have found hexagonal (2 × 2) superlattices as well as nonhexagonal superlattices, corresponding to a (√3 × 4) and a (√3 × √13) ordering of the alkali metal atoms at the surface. We have observed three equivalent rotational domains of the one-dimensional ordering, inclined at 120° with respect to each other, with domain sizes ranging from 100 to > 600 A ̊. Defects and irregularities were found at the very sharp domain boundaries as well as within the large domains of the one-dimensional phase. A possible transition process from the hexagonal (2 × 2) superlattice to the one-dimensional ordering, based on a dilution of the alkali metals atoms at the surface, is discussed. © 1990.