Electronic instabilities of the two-dimensional Sn/Ge(111) α-phase

The Sn/Ge(111) interface presents at room temperature an ordered root 3 x root 3R(30 degrees) surface reconstruction, formed by a submonolayer array of tin adatoms, which reversibly transforms upon cooling into a 3 x 3 structure. Recently, it has been claimed that the formation of a commensurate charge density wave is responsible for this transition. We present high-resolution synchrotron radiation photoemission results which support, instead, that the driving force of the transition is rehybridization: fluctuations in the tin adatom type of bonding freeze-in at low temperature to yield the static long-range ordering of the 3 x 3 ground state which is governed by an ideal 1/2 ratio of the sp(3)/sp(2) hybridization balance. (C) 1999 Elsevier Science B.V. All rights reserved.