Depth-resolved positron annihilation studies of argon nanobubbles in aluminum

The formation of Ar bubbles in Al has been investigated by using depth-resolved positron annihilation spectroscopy and transmission electron microscopy. Due to Ar bubble formation, the Doppler-broadening S parameter decreases, while the W parameter increases compared to the reference unimplanted Al sample. The effect of Ar ion fluence and annealing temperature on these parameters has been investigated. The presence of Ar at near-surface region has been confirmed by Rutherford backscattering spectroscopy. Transmission electron microscopy also shows that the Ar bubbles are in solid state with fcc structure after annealing at 870 K. The average diameter and lattice parameter of these solid Ar bubbles are estimated to be about 4±1 nm and 0.495±0.005 nm, respectively.