Surface-sensitive measurements of excitonic processes in rare gas clusters by electron energy loss spectroscopy

We present the electron energy loss spectra of Ar clusters as a function of cluster size ranging from 120 to 3500 atoms/cluster. The intensity of the bulk excitation peak decreases for cluster sizes larger than 500 atoms/cluster. This characteristic feature can be explained based on a simple calculation that takes into account the mean free path of the incident electrons. The present study demonstrates the promise of surface-sensitive measurements of the excitation processes of clusters