A critical review of the understanding of the reversible phase transition √3 x √3 ↔ 3 x 3 for the α-phase of the Sn/Ge(111) and Sn/Si(111) interfaces was presented. Experimental data and theoretical calculations suggest the following. (a) Sn/Ge(111) presents a reversible phase transition associated with the freezing of a surface soft phonon. At high temperature the dynamical fluctuations of the underlying 3 x 3 structure give rise to the observed √3 x √3 symmetry. (b) Sn/Si(111) did not present the 3 x 3 phase although the √3 x √3 reconstruction should be understood within the dynamical fluctuations model found for Sn/Ge(111). (c) These properties were modulated, but not substantially modified, by either defects or by electron many-body effects.

Dynamical Fluctuations and the √3 x √3 ↔ 3 x 3 Transition in α-Sn/Ge(111) and Sn/Si(111). J.Ortega, R.Pérez, F.Flores: Journal of Physics - Condensed Matter, 2002, 14[24], 5979-6004