Preparation of Al thin films charged with helium by DC magnetron sputtering

Helium atoms, up to 6.9 at.%, were introduced into Al films by DC magnetron sputtering in a He/Ar mixed atmosphere and distributed evenly in it. The relation between the He/Ar flux ratio, bias voltage, substrate temperature and helium concentration is studied. The helium concentration can be easily controlled by change of the process parameters and it greatly affects the morphology of film. TEM analysis suggests that small helium bubbles with a diameter of 1 nm are formed in the grain.