Dynamical fluctuations as the origin of a surface phase transition in Sn/Ge(III)

The Sn/Ge(111) interface has been investigated across the 3 x 3 -->, root 3 x root 3 R30 degrees phase transition using core level and valence band photoemission spectroscopies. We find, both above and below the transition, two different components in the Sn 4d core level and a bond splitting in the surface state crossing the Fermi energy. Theoretical calculations show that these two effects are due to the existence of two structurally different kinds of Sn atoms that fluctuate at room temperature between two positions and are stabilized in a 3 x 3 structure at low temperature.