Reflection of Noble Gas Ions at Solid Surfaces

A method was developed for distinguishing the reflection of ions at solid surfaces as ions or as metastable atoms. Results are given for He/sup +/, Ne/sup +/, and Ar/sup +/ ions incident on clean W, Mo, and Si(100) and on contaminated W, Hf, and Ge(111) surfaces. The reflection coefficient of ions to ions (R/sub ii/) is found to be small (0.0004 to 0.002) and essentially independent of incident ion energy. The reflection coefficient of ions to metastable atoms (R/sub im/) is found to increase with ion energy from values comparable to R/sub ii/ at 10 ev to values as high as 0.04 to 1000 ev. Discussion of these results is given in terms of the known resonance and Auger transitions which can occur near a solid-surface for ions of sufficiently large ionizatlon energy. It is shown that the results can be accounted for only if ions are transformed to metastable atoms very close to the surface, and a possible mechanism for this process is proposed. (auth)