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Disproportionation Phenomena on Free and Strained Sn/Ge(111) and Sn/Si(111) Surfaces

G. Ballabio·G. Profeta·S. de Gironcoli·S. Scandolo·G. E. Santoro·E. Tosatti
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Abstract

Distortions of the $\sqrt3\times\sqrt3$ Sn/Ge(111) and Sn/Si(111) surfaces are shown to reflect a disproportionation of an integer pseudocharge, $Q$, related to the surface band occupancy. A novel understanding of the $(3\times3)$-1U (``1 up, 2 down'') and 2U (``2 up, 1 down'') distortions of Sn/Ge(111) is obtained by a theoretical study of the phase diagram under strain. Positive strain keeps the unstrained value Q=3 but removes distorsions. Negative strain attracts pseudocharge from the valence band causing first a $(3\times3)$-2U distortion (Q=4) on both Sn/Ge and Sn/Si, and eventually a $(\sqrt3\times\sqrt3)$-3U (``all up'') state with Q=6. The possibility of a fluctuating phase in unstrained Sn/Si(111) is discussed.

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G. Ballabio, G. Profeta, S. de Gironcoli, S. Scandolo, G. E. Santoro, E. Tosatti. 2002-07-09. Disproportionation Phenomena on Free and Strained Sn/Ge(111) and Sn/Si(111) Surfaces. https://doi.org/10.1103/physrevlett.89.126803

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