The Fermi surface of Sn/Ge(111) and Pb/Ge(111)

The analysis of the electronic structure and Fermi surface of 0.33 monolayers (ML) of Sn/Ge(111) and Pb/Ge(111) has played an important role in understanding the phase transition from a room-temperature reconstruction to a (3 × 3) reconstruction below ∼200 K. Nowadays, the increasing resolution of image-type electron analysers enables us to obtain whole sets of constant-energy surfaces and energy-distribution curves. We review the electronic structure of Sn and Pb on Ge(111) and report high-resolution angle-resolved photoemission data for Sn/Ge(111)-(3 × 3) at 110 K. The results exclude nesting or any opening of a gap in the (3 × 3) phase at this temperature. From a comparison with density functional theoretical calculations, we conclude that the results on the electronic structure are only compatible with a (3 × 3) unit cell with one Sn atom displaced upward from the other two.