Temperature-Dependent Surface States and Transitions of Si(111)-7×7

Uv photoemission and electron-energy-loss measurements of Si(111)-7 × 7 between $T=15\mathrm{} \mathrm{and} 300$ K reveal significant temperature-dependent changes in the occupied surface states and their transitions which can be associated with electron-phonon coupling at the surface. Several new surface states and transitions are determined at low temperatures, including a highly localized (∼2-meV-wide), half-occupied state that resides within a 100-meV-wide surface-state band gap and determines the Fermi-level position.