Sputtering patterns and defect formation in alkali halides

We have separated the sputtering patterns of NaCl irradiated with low energy electrons into component features from the directional ejection of halogen atoms and a random evaporation of the metal atoms. The sputtering yields anti-correlate with exciton luminescence. Lifetime studies reveal the presence of several exciton states with different diffusion energies. The sputtering yield shows a resonance with the production of surface excitons. The experiments confirm the view that defect formation in the halogen sub-lattice proceeds by a non-radiative exciton decay which initiates a replacement collision sequence along a chain of halogen ions.