Ultrafast atomic diffusion inducing a reversible transition on Sn/Si(111):B

Here, we present experimental and theoretical evidence of a new reversible transition that takes place in Sn/Si(111):B. The system changes from an insulating (2 √ 3 × 2 √ 3)R30º structure at room temperature to a (√ 3 × √ 3)R30º symmetry above 520 K (2 √ 3 and √ 3 in the following). We explain this transition using a microscopic diffusive mechanism, where a Sn tetramer diffuses on the surface among 24 inequivalent ground states, giving rise to the √ 3 symmetry. This transition is reminiscent of other dynamical fluctuations transitions, but it includes as an essential novel ingredient the diffusion of Sn tetramers along the surface settling an order-disorder transition for the system.




Side and top views for the Sn/Si(111)B-2 √ 3 atomic structure. Large, medium, and small balls correspond to Sn (green) and Si (orange) first and second layer atoms, respectively; small grey balls in the side view represent B atoms. Inside the unit cell (indicated by black solid lines) Sn adatoms, lateral, and central tetramer atoms are plotted in different colors (brown, blue, and purple, respectively).

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