The defects which formed in alkali halide crystals that were subjected to low-energy electron bombardment were investigated by the simultaneous use of optical absorption, mass spectroscopic, and depth-profile surface sputtering techniques. The results showed that, at temperatures near to or below room temperature, F centers, small F-center clusters, and alkali metal clusters formed during electron bombardment. At temperatures of up to 400C, colloid formation (metallic phases in the bulk of crystal) occurred due to the higher mobility of the F centers. Depth profile measurements suggested strongly that the metallic phase was situated on the surface of the crystals whereas the F-center type defects formed in the bulk, or near to the surface. The surface clearly acted as an efficient trap for defects. The spatial distributions of point defects and metal were investigated at temperatures as low as -90C, where F-center mobility was negligible. The results revealed significant low-temperature metallization at the surface, and proved that long-range hot-hole diffusion took place during electron bombardment.

N.Seifert, S.Vijayalakshmi, Q.Yan, A.Barnes, R.Albridge, H.Ye, N.Tolk, W.Husinsky: Radiation Effects and Defects in Solids, 1994, 128[1-2], 15-26