Strain-induced structure transformations on Si(111) and Ge(111) surfaces: a combined density-functional and scannning tunnneling microscopy report

TL;DR

This study combines density functional theory and scanning tunneling microscopy to analyze how strain influences surface reconstructions of Si(111) and Ge(111), revealing phase diagrams and predicting structural transitions under strain.

Contribution

It provides the first calculated formation energy for unstrained Si(111)-9x9 surface and predicts surface reconstruction changes under tensile strain.

Findings

Surface transformations are explained by a strain-dependent phase diagram.

Unstrained Si(111)-9x9 formation energy is reported for the first time.

Si(111) is predicted to adopt a c(2x8) reconstruction under tensile strain above 0.03.

Abstract

Si(111) and Ge(111) surface formation energies were calculated using density functional theory for various biaxial strain states ranging from -0.04 to 0.04, and for a wide set of experimentally observed surface reconstructions: 3x3, 5x5, 7x7 dimer-adatom-stacking fault reconstructions and c(2x8), 2x2 and \sqrt{3}x\sqrt{3} adatoms based surfaces. The calculations are compared with scanning tunneling microscopy data obtained on stepped Si(111) surfaces and on Ge islands grown on a Si(111) substrate. It is shown that the surface structure transformations observed in these strained systems are accounted for by a phase diagram that relates the equilibrium surface structure to the applied strain. The calculated formation energy of the unstrained Si(111)-9x9 dimer-adatom-stacking fault surface is reported for the first time and it is higher than corresponding energies of Si(111)-5x5 and Si(111)-7x7 dimer-adatom-stacking fault surfaces as expected. We predict that the Si(111) surface should adopt a c(2x8) reconstruction when tensile strain is above 0.03.