The Photo-Electric Effect in Metallic Clusters

Small clusters of Silver atoms have been observed to yield about 100 times more photo-electrons than crystalline Silver (per unit area of surface) for photons with energy up to 1.5 ev above threshold. I have calculated the yield from Silver and Sodium clusters of up to 55 atoms using a Green's function formalism. A method of successive approximations takes into account the scattering of the electrons by the ion-cores as well as by the surface. The formalism is applied to an independent-electron model with a muffin -tin potential. Each electron feels the incident light wave and the polarization field of all the other electrons computed with the bulk dielectric function. Scattering of the photo-excited electron is included as a final step in the photo-emission process. The cross-sections calculated for Silver clusters are in good agreement with experiment; for Sodium clusters, however, the relevant experimental data are incomplete.