Atomic-Scale Study of Ge-Induced Incommensurate Phases on Si(111)

Two Ge-induced incommensurate phases, γ and β, on Si(111) are observed and studied by \it in situ scanning tunneling microscopy. The γ phase consists of aligned triangular domains whose stacking sequence is faulted with respect to the Si(111)-1×1 surface. The β phase consists of two kinds of triangular domains whose stacking sequences are faulted and unfaulted with respect to the Si(111)-1×1 surface, respectively. In the β phase, two types of domain walls, ``zigzag'' and ``face-to-face'', form to release the strain. The triangular domains all exhibit a quasi-1×1 hexagonal close-packed structure. By studying the structural evolution from magic clusters to incommensurate structures, the structure models for γ and β phases are proposed.