Surface-state band structure of the Si(100)2 x 1 surface studied with polarization-dependent angle-resolved photoemission on single-domain surfaces.

Abstract

The electronic structure of the Si(100)2\ifmmode\times\else\texttimes\fi{}1 surface has been studied with polarization-dependent angle-resolved photoemission. By using vicinal Si(100) samples, single-domain 2\ifmmode\times\else\texttimes\fi{}1 surfaces were obtained, and the surface-band dispersions were measured unambiguously along the symmetry axes \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}-J\ifmmode\bar\else\textasciimacron\fi{}' and \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}-J\ifmmode\bar\else\textasciimacron\fi{} in the surface Brillouin zone (SBZ). The obtained dispersions are compared to dispersions from earlier studies of two-domain surfaces, as well as to theoretical band-structure calculations. In addition to the well-known surface state attributed to the dangling bonds, five more surface-related structures were observed on the single-domain surface. One of these is the controversial surface state previously observed on two-domain surfaces at J\ifmmode\bar\else\textasciimacron\fi{}' in the [010] direction at \ensuremath{\sim}0.9 eV below the Fermi level (${\mathit{E}}_{\mathit{F}}$), which is not accounted for in any calculated surface band structure for the Si(100)2\ifmmode\times\else\texttimes\fi{}1 surface. Contrary to a previous report, it is also observed on the single-domain surface at several points in the SBZ.The second additional structure was found to disperse downwards along the \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}-J\ifmmode\bar\else\textasciimacron\fi{}' line, to a minimum energy of 3.4 eV below ${\mathit{E}}_{\mathit{F}}$ at J\ifmmode\bar\else\textasciimacron\fi{}'. It is interpreted as a back-bond resonance. The third additional structure was seen as a faint peak at the Fermi level in normal emission. Finally, two other surface-related structures were found in the \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}-J\ifmmode\bar\else\textasciimacron\fi{} direction, one at \ensuremath{\sim}-1.3 eV at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} in the second SBZ, splitting into two peaks for higher ${\mathbf{k}}_{\mathrm{?}}$ values. By using a linearly polarized light source, the symmetry properties of the surface states and resonances were determined along the symmetry axes \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}-J\ifmmode\bar\else\textasciimacron\fi{}' and \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}-J\ifmmode\bar\else\textasciimacron\fi{} in the SBZ. The polarization dependence for several states indicates a mirror symmetry along these directions, with the dangling-bond state having even parity in both directions, in agreement with theoretical predictions for symmetric dimer models, and the back-bond resonance having odd parity in the \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}-J\ifmmode\bar\else\textasciimacron\fi{}' direction. Three of the surface states and resonances are not accounted for in theoretical band structures for the 2\ifmmode\times\else\texttimes\fi{}1-reconstruction. Two of these can be explained by domains of asymmetric dimers, arranged into c(4\ifmmode\times\else\texttimes\fi{}2) or p(2\ifmmode\times\else\texttimes\fi{}2) periodicities.