Surface soft phonon and the root3 x root3 <--> 3 x 3 phase transition in Sn/Ge(111) and Sn/Si(111)

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  • 14 November 2000
Abstract
Different mechanisms, like Peierls transitions or Charge Density Waves, have been proposed as the origin of particular symmetries at semiconductor surfaces. Using Density Functional Theory (DFT) calculations, a soft phonon has been identified, for the first time, as the mechanism describing a surface phase transition: the reversible Sn/Ge(111) root 3 x root 3 <--> 3 x 3. We have also considered the similar isovalent Sn/Si(111) case and have found that it corresponds to a non-completely developed soft--phonon, whose partial softening explains the strong experimental similarities with the Sn/Ge system at room temperature.Surface phonon dispersion relations for this mode are given for both interfaces.

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