Metal/semiconductor incommensurate structure with a rare domain configuration exhibiting p31m symmetry

An incommensurate overlayer structure on a Ga/Si(lll) surface, which can be identified with the 6.3 root 3 x 6.3 root 3R30 degrees superstructure obse rved by the electron diffraction method, has been directly observed using s canning tunneling microscopy. The domain-wall pattern of this structure con sists mainly of an array of isolated triangles, in contrast to the meshlike network usually observed on an incommensurate overlayer. A particular feat ure of this structure is that it assumes a rare domain configuration with p 31m symmetry, rather than the p3m1 symmetry of the underlying Si(lll) doubl e layer, to relax the strain induced by its relatively high Ga coverage.