Shifts and widths of metal-overlayer quantum-well states near ${\mathit{E}}_{\mathit{F}}$ observed by photoemission

Photoelectron energy spectra reveal discrete valence-electron states in the range 0–220 meV above ${\mathit{E}}_{\mathit{F}}$ for 1–3 atomic layers of Na on Cu(111). Apart from a stepwise dependence on the number of atomic Na layers the energy of the quantum-well states depends in a gradual manner on how full the layer is. The states are as well defined in energy as comparable surface states producing peak widths (50–90 meV), which depend on temperature and coverage.