Growth of He bubbles in Al during annealing

The temperature dependent growth of He bubbles in Al films implanted at room temperature to various He concentrations is investigated by electron energy-loss spectroscopy (EELS) and transmission electron microscopy (TEM). EELS reveals even the weakest changes in He density within the bubbles by measuring the pressure shift of the He 11S0-21P1 transition. This is applied to investigate the mechanisms driving the growth of bubbles in the temperature range 20 deg C < or approx. T < or approx. 500 deg C. For T < or approx. 200 deg C indication is found that bubbles relax by emission of interstitial dislocation loops. At higher temperatures bubble migration and coalescence under absorption of thermal vacancies is evident. The final state is characterized by large cavities filled with He at low pressure as evidenced by the detection of the atomic He series. (author)