Reactive germanium/transition metal interfaces investigated with synchrotron radiation photoemission: Ge/Ni and Ge/Pd

We report the first photoemission studies of the electronic structure at the interface between Ge(111) and d-metal overlayers at monolayer coverages. Two systems are discussed, Ge(111)/Pd and Ge(111)/Ni. In the case of Ge(111)/Pd a broad, reacted germanide-like phase is formed with similar electronic features to the Si(111)/Pd interface. In the Ge(111) Ni case an evolution of the valence band structure versus coverage from a reacted situation to a metal rich situation is found, indicating a strong gradient of concentration. The interface is narrower than for Ge/Pd. Photoemission spectra of the valence band at hv=80 eV are presented as well as core line data of the Ge 3d which show the trends in binding energy shifts and the changes in the relative intensities as a function of metal coverage. The discussion is carried out on the differences in the growth of these interfaces and comparisons are made to the correspondent silicide/metal systems.