The structural and electronic properties of platinum–germanide on Ge(111)

We report a scanning tunneling microscopy and spectroscopy study of the formation of platinum–germanide phases on Ge(111). Platinum was deposited on Ge(111) at room temperature and subsequently annealed at temperatures varying from 773 K to 1173 K. At annealing temperatures below 1073 K, disordered germanide islands are found on the terraces. However, at temperatures above 1073 K a new germanide phase nucleates at the pre-existing step edges of the Ge(111) surface. The electronic structure of this germanide phase exhibits band gaps below −2.2 eV and above 1.8 eV with respect to the Fermi level. In addition, several well defined electronic states are resolved within the energy range from −2.2 eV to 1.8 eV. We interpret these observations within the framework of the nearly free electron and quantum well state models.