Sublinear effect in electron emission from solids bombarded with swift gold clusters

A sublinear effect in the secondary electron emission from insulating solids under impacts of gold clusters (Au)(n), n = 1-5, with energy E = 33-11000 keV/atom has been observed experimentally using the ARAMIS and Tandem accelerators at Orsay. The effect manifests itself in the decrease of the number of emitted electrons per cluster atom with the increase of the number of atoms in the cluster and the projectile energy. We explain this phenomenon by a mechanism of sweeping-out electrons, which causes a decrease in the number of available electrons in the solid, after the passage of the forward atoms of the cluster through the atomic layers from which the electrons can be emitted. Calculated absolute values of the sublinear effect as well as its dependencies, based on the theory of secondary electron emission, are in agreement with the experimental data.