TRAPPING OF IONS AT METAL-SURFACES

The surface trapping probability S(E-i) of Na+ on Cu(001) has been mea sured for incident energies E-i between 5 and 600 eV via resonant ion neutralization for both 45 degrees and 8 degrees incidence. For 8 degr ees incidence, S(E-i) decreases with increasing energy. For 45 degrees incidence, however, S(E-i) decreases to zero at approximately 25 eV, and then increases with increasing energy up to 125 eV. We explain thi s behavior in terms of the changing surface corrugation seen by an ion as its energy increases.