Stereo-electron microscopy of low-energy ion-bombarded gold

Abstract

Gold foils with stated purities of 99·999% and 99·9999% containing vacancy stacking-fault tetrahedral were irradiated inside an electron microscope with 300 eV Xe+ ions. It was found that tetrahedral ≳ 1000 A from the irradiated surface were affected by the irradiation at temperatures as low as 25°K. The mode of shrinkage of the tetrahedral was examined and found to be different at 77°K and below, and above 200°K. This transition is associated with the onset of interstitial migration across a stacking fault. The total amount of vacancy loss and the depth dependence of vacancy loss, as determined by stereomicroscopy, were found to be essentially independent of temperature from 25°K to 283°K but were clearly different for the two materials of different purities. In addition interstitial clusters were observed, and the observed density was correlated with temperature and material purity. These results are consistent with a model in which interstitials are mobile throughout the temperature range investigated, while impurities act as deep traps for these defects. The results put extremely severe constraints on other models for interstitial production and migration in gold, which are examined in some detail.