INITIAL GROWTH OF SILVER ON GE(111) STUDIED BY SCANNING-TUNNELING-MICROSCOPY

Scanning tunneling microscopy (STM) has been used to study the Ge(111) surface after submonolayer depositions of Ag. At the lowest coverages a (4 X 4) reconstruction, with small insets of a (3 X 1) edge structure, is observed. Based on the STM images we propose a mixed Ag and Ge adatom structure for the (4 X 4) reconstruction, in which the adatoms have local (1 X 1) and (2 X 2) arrangements corresponding to a Ag coverage of 6/16 monolayers. The (3 X 1) structure appears to have a configuration similar to the Si(111)/Ag-(3 X 1) reconstruction, although in this case it has a much more limited extension, restricted to a few unit cells in the near vicinity of step edges and phase boundaries. At higher coverages, after the completion of a full (4 X 4)/(3 X 1) surface, a (square-root 3 X square-root 3)R 30-degrees structure appears showing STM images similar to those previously published for the Si(111)/Ag system.