Photoexcitation of resonances in Ag films on Ni(111)

Angle-resolved photoelectron spectra from Ag films supported on a Ni(111) substrate show interesting behavior in response to variation of the photon energy. In contrast to previous reports of discrete and dispersionless quantum-well states in metal films,the Ag/Ni system supports quantum-well resonances that exhibit ``ratcheting'' energy dispersions and oscillatory emission intensities. These observations are reproduced in a model calculation taking into account both the initial and final continuums of states involved in the photoexcitation process.