MULTIPLY IONIZED ATOM PRODUCTION IN KEV-N+-SI-SURFACE SCATTERING

A definite energy threshold is found for the appearance of doubly and triply charged ions when N+ ions are elastically scattered from surface atoms in a clean silicon surface. These threshold energies directly confirm the model in which multiply charged ions are created in binary encounters by molecular-orbital electron promotion, and then axe partially neutralized as they leave the surface. Characteristic velocities for neutralization of scattered N2+, N+ and recoiled Si3+, Si2+, Si+ ions in silicon are in the same range as have been found for rare gas and metal ions. For each element they seem to scale roughly as the square root of ionization potential of each charge state, but there appears to be no other systematic dependence.