In situ TEM observation of helium bubble evolution in V/Ag multilayer during annealing

Multilayers have been considered as promising candidates for nuclear materials. In this paper, an in situ study on the growth of helium bubbles during annealing was performed by transmission electron microscopy. Bubbles in the Ag layers grew rapidly by vacancy absorption mechanism and reached a size comparable to the layer thickness, whereas bubbles in the V layers evolved slowly due to the lower diffusion rate of vacancies and stopped growing at the size of 1.8 nm. The interfaces with more than one orientation relationship in the V/Ag multilayer contained pockets of excess volumes that can readily trap helium and exhibit high helium solubility. The interfaces prevent bubbles from growing into nearby layers.