Interstitial defect clusters in gold after bombardment with 270 eV gold ions

Abstract

The formation of interstitial atom clusters in gold foils due to low energy gold ion bombardment was investigated using transmission electron microscopy. Essentially no damage was produced in specimens having relatively clean surfaces by bombardments between + 100°c and -30°c. At lower bombardment temperatures in the range -30°c to -90°c significant damage appeared at a density which increased gradually with decreasing temperature. The possible role of impurities in nucleating the interstitial damage clusters was investigated by bombarding specimens with argon ions, and also by intentionally contaminating the specimen surfaces by exposure to electron or ion beams in the presence of hydrocarbon vapours prior to (or during) gold ion bombardment. The argon bombardment and surface contamination caused considerably higher densities of damage than were found in the clean gold bombarded specimens. In agreement with other investigators it is concluded that the damage in ion bombarded gold is formed by the aggregation of interstitial point defects driven into the foils by replacement collision sequences. However, the results of the present work indicate that damage is nucleated by hydrocarbon or argon impurities which are driven small distances into the specimen surfaces. Once nucleated, inward growth of clusters occurs by the accretion of point defects. A temperature dependence of the damage near 0°c in argon ion bombarded specimens therefore cannot be taken as evidence for the onset of interstitial point defect mobility near this temperature, as previously supposed by several investigators. In fact, the present results are consistent with an interstitial which is already highly mobile below -90°c.