Defects observed by electron microscopy in gold bombarded with keV gold ions I. Nature of defects

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Abstract
The nature of small defect clusters produced in single crystal gold films by room temperature bombardment with 3 to 40 keV gold ions incident along [001] channeling directions to doses of 109 to 1012 ions cm−2 was investigated using transmission electron microscopy. The number of observed defects per measured incident ion rose from about 0.03 at 3 keV to ∼ 1 defect per ion for ion energies >10 keV. Above 15 keV, closely spaced groups of multiple clusters produced by individual ions were observed in significant numbers. Stereo microscopy showed that essentially all of the defects were produced within about 300 Å of the bombarded surface. Application of the defect contrast analysis of Wilkens and Rühle(5,13) for identifying the nature of small defects revealed that the visible defects were vacancy type over the entire range of ion energies used. Above 15 keV the defects were mainly dislocation loops; below 15 keV they appeared to be centers of dilatation. These results are contrasted with observations by Diepers(4) and Diehl et al.(5) of interstitial dislocation loops in copper and gold bombarded with 1–5 keV argon ions and with previous work (Merkle(7,8) and Noggle and Oen(9)) suggesting that a threshold knock-on energy of about 25 keV exists for the formation of a visible cluster in gold. Finally, models are proposed for the production of defect clusters in ion bombarded gold as a function of incident ion energy and specimen purity.