Electronic properties of (2 x 1) and c(4 x 2) domains on Ge(001) studied by scanning tunneling spectroscopy.

The surface electronic structure of Ge(001) was studied by scanning tunneling spectroscopy. The measured surface densities of states unequivocally reveal the presence of a metallic state on the (2 x 1) domains, which is absent on the c(4 x 2) domains. This metallic state, so far observed only in integral measurements, is attributed to the flip-flopping dimers that constitute the (2 x 1) domains. Our data also reveal a set of previously unresolved surface states, in perfect agreement with published theoretical predictions.