Defects observed by electron microscopy in gold bombarded with keV gold ions II. Mechanism of defect formation

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Abstract
Further electron microscopy studies were made of the vacancy type defects produced in gold thin films by keV gold ion bombardment along channeling directions at room temperature as described in Part I. It was found that the defect density increased linearly with dose, and that the defect size distribution was independent of dose for a given ion energy. The average defect size increased with increasing ion energy. Measurements of the defect depth distributions below the surface were also made for bombardments along a fixed direction (i.e. [001]) as a function of energy (5–120 keV) and for bombardments of fixed energy (40 keV) as a function of channeling direction (i.e. [111], [001], and [011]). The distributions were all sharply peaked below the surface. It was concluded that serious glissile defect losses to the surface occurred within 100–200 Å of the surface. Considerable evidence in the literature supporting this conclusion was cited. The defect depth distributions in the regions unaffected by surface losses were compared with the corresponding ion penetration data, and reasonably good agreement was found. The results indicated that: (1) essentially all of the observed defects were produced beyond the range of randomly colliding incident ions and were therefore caused by channeled gold ions; (2) the defects were formed in situ at displacement cascades initiated by the dechanneling of incident channeled gold ions by thermally displaced atoms; (3) the stopping of channeled gold ions in gold at room temperature by dechanneling at thermally displaced atoms is a major stopping mechanism in the energy range where nuclear stopping is important.