Dynamical fluctuation and surface phase transition at the Sn/Ge(111) root 3 x root 3R30 degrees-alpha interface

The root 3 x root 3R30 degrees-alpha surface phase of Sn/Ge(lll) transforms reversibly upon cooling into a 3 x 3 phase. Using high-resolution photoemi ssion, the effect of this transition on the Sn core-level and the Fermi sur face (FS) has been determined. The topology of the FS show a Fermi momentum along T (K) over bar and T (M) over bar of 0.27 +/- 0.02 Angstrom(-1) and 0.30 +/- 0.02 Angstrom(-1), respectively. In the low-temperature phase, a w ell-resolved core-level splitting is observed for the Sn adatoms. Our data are consistent with a local-bonding representation, when the transition is driven by freezing of dynamic fluctuations of two inequivalent types of Sn adatoms, coexisting at room temperature. (C) 2000 Elsevier Science B.V. All rights reserved.