Gas bubbles in beryllium implanted with He ions at temperatures <= 700 K and after post-implantation annealing

Helium bubbles in beryllium implanted with 5 and 15 keV He ions at temperat ures, T-irr, from 300 to 700 K before and after post-implantation annealing at temperatures, T-ann, up to 1100 K have been studied by TEM, Tiny overpr essurized He bubbles are observed for T-irr less than or equal to 500 K. At T-irr = 700 It the bubbles are larger and mainly facetted. At higher fluen ces coarser and flattened-out gas cavities and labyrinth systems are develo ped. a qualitative explanation of He reemission data at different irradiati on temperatures based on these observations is suggested. An estimate of th e dissociation temperature of HeV complexes in Be gives a value of 900 K. T he development of the gas porosity during annealing of Be implanted with He ions at T-irr less than or equal to 500 K demonstrates features similar to those of fcc-Ni and Cu, in which a part of He bubbles maintain their overp ressure up to 70% of the melting point. Ion irradiation leads to an enhance d growth of a microcrystalline surface layer of cph-BeO which is suspected to act as a barrier for the permeation of thermal vacancies. Finally, the a ppearance and the parameters of helium bubbles are compared with those of d euterium filled cavities developed under equivalent conditions and the diff erences are discussed. (C) 1998 Elsevier Science B.V. All rights reserved.