The electronic structure of the valence and conduction bands at the Si͑100͒ surface has been studied by two-photon photoemission over a wide photon-energy range. The ionization energy was determined to 5.40 Ϯ0.03 eV. The occupied surface state at ⌫ is placed 0.15Ϯ0.06 below the valence-band maximum. Several other spectral features are assigned to transitions involving surface states and between bulk bands including backfolded bands due to the surface reconstruction. The moderate agreement between experimental data and band-structure calculations calls for an improved theoretical description of the two-photon photoemission process at semiconductor surfaces incorporating, e.g., a one-step model and excitonic effects.

The occupied and unoccupied electronic structure of thin epitaxial CoSi(2) films grown on Si(111) substrates was studied using time-resolved two-photon photoemission and valence-band photoemission spectroscopy. The work function of the sample surfaces and the Schottky barrier height at the metal-semiconductor interface were measured as a function of annealing temperature. The photoemission data reveal several occupied and unoccupied electronic states which exhibit a high sensitivity to the annealing temperature. Time-resolved measurements show a behavior typical for a short-lived hot-electron gas and indications for an image-potential resonance.

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