Energy Spectra of Electrons Induced by MeV Atom Clusters

The first observation of the energy distribution of electrons emitted from solids bombarded by MeV atom clusters is reported. In the backward direction, using graphite and Si bombarded by C n + and Al n + ( n ≤8), an appreciable suppression of electron emission has been observed at electron energies lower than ∼10 eV. Electron yield per atom decreases with increasing n , and becomes less than 50% at n ≥3, relative to the case of n =1. The experimental results cannot be explained in terms of projectile stopping cross sections nor by the clearing-the-way effect. It is probable that the suppressed electron emission is a result of the suppression of the transport or surface transmission of the produced low-energy electrons, rather than of the suppression of ionization.