Tunneling Images of Germanium Surface Reconstructions and Phase Boundaries

We have imaged with the tunneling microscope the microscopic surface topography of germanium layers grown by molecular-beam epitaxy on Si(111)-7×{}7. The surface structures corresponding to Ge(111)-c2×8 and Ge(111)-7×{}7 are resolved. The Ge-c2×8 structure is shown to consist of a coherent combination of two simpler units both of which exist independently on the surface. The associated phase boundaries are illustrated. The Ge 7×{}7 structure is shown to be similar to that obtained for Si(111). Defects in the cell are also imaged.