Periodicity and thickness effects in the cross section of quantum well states

The photoemission cross section of quantum well states in very thin Cu film s has been analyzed as a function of photon energy within a wide energy ran ge. We show that this cross section is periodical in k space, peaking aroun d vertical transitions of the respective Cu bulk band. The cross section pe ak width is analyzed in terms of final- and initial-state wave vector broad ening. The latter can only be detected at low kinetic energies due to reduc tion of final state broadening. The initial state k(perpendicular to) broad ening increases when the Cu film gets thinner, as simply expected from the uncertainty principle.