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

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