Desorption and Secondary Ion Production During Bombardment of CO/Ni(111) with Ne+ and Ne++ Ions at Very Low Impact Energies

Abstract

We have studied ion — induced desorption at very low impact energies. Singly and doubly charged Ne ions with impact energies E0 between 20 eV and 500 eV have been used. The desorbing species (neutrals and ions) have been analysed by means of a quadrupole mass spectrometer. The desorption cross section σCO for neutral CO which is desorbed predominantly was determined for different impact energies and impact angles. When using doubly charged Ne ions instead of singly charged ones, no difference in the desorption cross section for neutral CO could be found. For impact energies below 100 eV the secondary ion yield of CO+ and Ni+ was found to be higher for bombardment with Ne++ than for Ne+. As an explanation, we propose an additional, new mechanism for secondary ion production; the particle emission is caused by momentum transfer during binary collisions, accompanied by ionization via electron capture by the primary ion from the sputtered particle.