Probing unoccupied bulk bands via the cross section of quantum well states in thin films

The photoemission cross section of quantum well states in thin Cu(1 0 0) films on Co(1 0 0) has been analyzed in normal emission as a function of photon energy. Assuming conservation of the perpendicular wave vector k⊥, the cross section maxima can be assigned to direct transitions from the (initial) quantum well state to bulk-like final states. The value of k⊥ is obtained from the sharp k⊥ distribution of specific quantum well states, which is centered about discretized k⊥ values. Our data are compared with free-electron-like models and a low energy electron diffraction calculation of high-energy states in bulk Cu.