Femtosecond time-resolved studies of image-potential states at surfaces and interfaces of rare-gas adlayers

For rare-gas layers of sufficient thickness new electronic states arise from the screened image-potential of the metal within the adlayer. These states have similar properties as the image-potential states on clean surfaces, but are spatially located at the dielectric/metal interface and can have energies above the vacuum level. We discuss the origin and the basic properties of these previously unexplored interface states for the system Ar/Cu(1 0 0). We will show how time-resolved 2PPE can be used to study their decay by resonant tunneling through the layer into vacuum and by electron-hole-pair decay into the metal.