An electron microscope study of helium bubble diffusion in gold

Abstract

The diffusion of small helium bubbles in gold, formed by room temperature implants of 200 eV helium ions, has been followed during electron microscopy in-situ annealing. Brownian motion of bubbles has been directly observed together with their loss to the nearby surface. The results of an isochronal study have been modelled and analysed in terms of both surface diffusion and ledge nucleation controlled bubble diffusion. Although the data was limited, both mechanisms led to surface diffusion activation energies of the order of 1 eV. However, the combination of the new data with the detailed 1133 K D b measurements given by Willertz and Shewmon favoured direct surface diffusion controlled bubble diffusion. The best value for D s was given by D s = 7.4 × 10 −5 exp(−1.23/ kT) cm 2/s. Information obtained from bubble data for gold appears to conflict seriously with the previous values obtained in surface grooving studies.