STM study of the structure and phases of Pb on Ge(111)

The different structures of Pb on Ge(111) have been studied as a function of Pb-coverage up to two monolayers with scanning tunneling microscopy. At low coverages a c(2 × 8) and a (√3 × √3)R30° reconstruction with a mixture of Pb and Ge adatoms both occupying T4-sites was observed. The bias voltage dependence of topographic images of these structures is interpreted in terms of a charge transfer between the different adatom dangling-bond orbitals. On the basis of the STM images new structural models for the metastable (4 × 4) reconstruction and the higher density (√3 × √3)R30° reconstruction are proposed. In addition a previously unobserved striped incommensurate phase was found for coverages greater than 43 monolayers. The data from this striped phase are compared with the predictions of domain-wall theory for commensurate-incommensurate phase transitions