Overlayer resonance and quantum well state of Cs/Cu(111) studied with angle-resolved photoemission, LEED, and first-principles calculations

Artikel i vetenskaplig tidskrift, 2007

Angle-resolved photoemission spectroscopy and low-energy electron diffraction are used to study submonolayer coverages of Cs on Cu(111) at room temperature (RT) and 170 K. At RT, the Cs saturation coverage is approximately 90% of the full monolayer coverage. The full monolayer is characterized by a quantum well state (QWS) band having an energy of 25 meV below the Fermi level (E-F) in the (Gamma) over bar point and a resonance band extending to energies below the Cu band gap. This is supported by our first-principles calculations. Low-energy electron diffraction shows that the Cs overalyer forms a (2x2) structure over a wide coverage range, in which the QWS has energies from 50 meV above to 25 meV below E-F. The continued energy shift of the QWS after saturation of the diffraction angles is interpreted in terms of vacancies in the overlayer.