Femtosecond dynamics of final-state effects in the valence band photoemission of silver clusters on a graphite substrate

We studied the electronic structure of quasi size-selected silver clusters grown in nanopits of a graphite surface using ultraviolet photoelectron spe ctroscopy at T = 40 K. For clusters with more than 9 x 10(2) atoms the init ial state of the d-electrons has already reached the bulk limit, but there is a dynamic final-state effect which we can explain with a simple model ta king into account the finite lifetime of the photohole (corresponding to a charged cluster) and the cluster-substrate interaction on a femtosecond tim escale. Below a critical cluster size of about 5 x 10(2) atoms we have obse rved additional initial-state effects.