In-Situ Evolution Of Helium Bubbles In Sic Under Irradiation

The evolution of individual He bubbles in 4H-SiC thin foils during irradiation with 1.5 MeV Au ions has been studied by in-situ transmission electron microscopy. During irradiation, individual He-bubbles under displacement damage were observed to gradually decrease in size at different rates due to their position within the thin foil. In the bulk, slow bubble shrinkage at a constant rate can be explained by a competition between direct displacement of He out of the bubble and re-trapping, while the bubble remains at equilibrium pressure. A 1D-model proved that half of the ejected-He is re-trapped during the displacing irradiation. At high irradiation dose, the excess of vacancies due to bubble shrinkage and the vacancies provided by the irradiation itself leads to the formation of small satellite bubbles. The system thus evolves toward a steady state of bubble size with all the helium atoms in the matrix. In thin parts, bubbles showed a faster shrinkage rate with little or no re-trapping before quick disappearance. (C) 2015 AIP Publishing LLC.