QUANTUM-SIZE EFFECTS IN ULTRATHIN CU(100) FILMS

We report an angle resolved photoemission study of quantum size effect s observed in the electronic structure of pseudomorphic Cu(100) films. The 3d band of a one-layer film exhibits an 80% reduction in its perp endicular dispersion and a 10% reduction in its parallel dispersion. T he perpendicular dispersion of the 3 d band evolves rapidly with incre asing film thickness, since the 3 d electrons are strongly localized o n the ion cores. Quantum-well resonances are produced due to the discr etization of the perpendicular wave vector in the s,p band. They produ ce oscillations in the Fermi level intensity as they disperse through it when the film thickness is increased. The observed oscillation peri od of approximately six layers matches that of oscillations in the mag netic exchange coupling between ferromagnetic Co films separated by Cu spacer layers. The connection of the quantum-well states to bulk elec tronic structure is determined by comparing oscillation amplitudes for two different photon energies.