Surface phonons of S:Si(001)-(1×1)

Abstract

We present results of ab initio calculations of vibrational properties of the Si(001) surface covered by a monolayer of sulfur. The S:Si(001) system is a prototype of chalcogen adlayers on (001) surfaces of Si or Ge. Our results highlight all features characteristic for the whole class of such adsorption systems. We find a number of pronounced localized surface phonon modes as well as resonances part of which are characteristic for the adlayer while others are directly related to the substrate surface. The physical origin and nature of these modes is discussed employing surface phonon dispersions, atomic displacement patterns, respective charge density perturbations, and spectral phonon densities. In our calculations, the surface is modeled within the supercell approach and we use pseudopotentials together with a plane wave basis set. The surface phonon properties are calculated within density functional perturbation theory.