Trapping and release of D from “saturated” implants in graphite

Abstract

Monoenergetic implants of hydrogen ions in graphite are known to form saturated layers with a thickness corresponding to the ion range. The saturation concentration which was originally assumed to be independent of depth, has been found to be considerably lower in the near surface part of the range than at or beyond the mean projected range. This effect can be demonstrated by observing the trapping and release behaviour during implantation with D +-ions of changing energy. We have observed the additional trapping of 3 keV D +-implants into layers saturated with 6 keV and the subsequent increase to re-emission coefficients R > 1 when this layer is again bombarded with 6 keV D +. The R > 1 behaviour is found in a temperature range between 300 and 700 K using re-emission spectroscopy of D 2, HD and CD 4. The results are discussed in terms of theoretical models for trapping and release.