STM STUDY OF THE INCOMMENSURATE STRUCTURES OF PB ON GE(111) AND SI(111) SURFACES

The incommensurate structures of Pb on Ge(111) and Pb on Si(111) have been investigated at room temperature with scanning tunneling microsco py. On most Ge(111) samples a striped incommensurate phase was observe d for Pb-coverages just above 4/3 ML. However, evidence for the existe nce of an additional incommensurate phase with hexagonal symmetry was also found. The STM image of the hexagonal phase can be interpreted as a moire pattern formed between the adlayer and the substrate. In the case of Pb on Si(111) we observed both hexagonal and striped incommens urate phases. Surprisingly, six different commensurate subdomains were found in the striped phase, which indicates that there are two differ ent adsorption sites.