Band structure and electron gas of In chains on Si(1Â 1Â 1)

The quasi-one-dimensional electron gas is studied for chain arrays on In/Si(1 1 1)4 × 1 and 4 × 2 surfaces using first-principles electronic-structure calculations. The band-structure calculations indicate a metallic (4 × 1) and a semimetallic (4 × 2) surface system. The latter result contradicts the interpretation of recent photoemission measurements. The partial occupation of the surface bands gives rise to an electron gas with an ill-defined dimensionality but a strong anisotropy. The square of the anisotropic plasma-frequency varies significantly between the directions parallel and perpendicular to the chains. We discuss consequences for the electrical conductivity, optical reflectance anisotropy and electron-energy losses and compare with available experimental data. The results and the comparison with experiments clearly indicate gap openings and a reduction of the metallicity during the phase transition 4 × 1 → 4 × 2 but not an insulating 4 × 2 phase.