Symmetrizing evolution of dimer structures on tensile-strainedSi(001)surfaces: First-principles density-functional calculations

Abstract

Using density-functional theory calculations, we investigate the symmetry evolution of asymmetric surface dimers on $\mathrm{Si}(001)$ according to the applied tensile strain. As the strain increases, the asymmetry of the surface dimers decreases and the surface geometry is rearranged. We find a new surface reconstruction of $\mathrm{Si}(001)$ with alternating asymmetric dimer and symmetric dimer (ADSD) along a dimer row. The ADSD structure is more stable than the symmetric dimer (SD) or asymmetric dimer (AD) structure under 6.2--16% of biaxial strain and 7.5--23% of uniaxial strain. Under higher strain, the surface dimers are fully symmetrized and become SDs. Electronic structure analysis reveals that the stabilization of the ADSD structure is correlated with the surface band gap closing of AD surfaces under tensile strain and the strong $\ensuremath{\pi}$ interaction on SD surfaces.