Electronic structures in unoccupied states of Bi thin film studied with two-photon photoemission spectroscopy

We have performed synchrotron-radiation angle-resolved photoemission and angle-resolved two-photon photoemission (2PPE) study of Bi(1 1 1) films with the thickness of 12 bilayers grown on Si(1 1 1) – 7 × 7. From the detailed analysis of the excitation energy dependence of angle-resolved 2PPE spectra, we have determined the electronic structures in the occupied and unoccupied regions. The observed electronic structures in the unoccupied states above the Fermi-energy were attributed to the quantum-well states originate from the quantization of the 6p-derived bulk bands.