HELIUM BUBBLE FORMATION IN NICKEL DURING HOT IMPLANTATION

Bubble formation in Ni during He implantation is studied in dependence upon temperature and He production rate. For three different helium p roduction rates (9, 50 and 260 appm h(-1)), the temperature has been v aried between 523 and 1050 K. The nominal helium content in each case after implantation was 100 appm. Subsequently performed TEM investigat ions yielded monomodal bubble size distributions. The measured bubble densities and mean radii show Arrhenius behaviour in a low temperature regime characterized by low apparent activation energies and in a hig h temperature regime characterized by high apparent activation energie s. These activation energies provide evidence that the low temperature regime is controlled by He diffusion via the self-interstitial/He rep lacement mechanism and the high temperature regime is He dissociation controlled according to standard nucleation models. For the high tempe rature regime also the rate dependencies confirm these findings. We co mpare our results with other experimental findings.