HI-ERDA versus SIMS to study helium profiling in pure bcc metals

(1) Service de Recherches de Métallurgie Physique, Direction de l'énergie nucléaire, CEA, F-91191 Gif-sur-Yvette, France.
(2) Laboratoire JANNUS, Service de Recherches de Métallurgie Physique, Direction de l'énergie nucléaire, CEA, F-91191 Gif-sur-Yvette, France.
(3) Groupe d’Etude de la Matière Condensée, CNRS-Université de Versailles Saint-Quentin-en-Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles Cedex, France.
Helium effects on microstructural and mechanical properties are key issues in fission or fusion materials research. Due to its extremely low solubility in most metallic alloys, helium strongly interacts with pre-existing and radiation-induced defects, leading to structures degradation. In order to extend the longevity of structural materials in the advanced reactors, it is necessary to comprehend the helium diffusion down to the atomic-scale.

Pure bcc metals (V, Fe, Ta, Nb and Mo) were implanted with 4He+ ions at energies ranging from 45 keV to 90 keV with a fluence equal to 5x1016 ions/cm2. After implantation, He depth profiles were deduced either from high energy heavy ion-induced elastic recoil detection analysis (HI-ERDA) or from secondary ion mass spectrometry (SIMS) profiles. Both techniques give similar results: all samples exhibit a projected range of around 200 nm, in agreement with TRIM theoretical calculations. The latter results were then compared with the He bubble distribution obtained by Transmission Electron Microscopy (TEM).  TEM micrographs reveal that the nanometric bubbles are homogeneously distributed in the microstructure.

The main aim of this study is to compare the experimental conditions and performances allowed by the use of HI-ERDA and SIMS in quantitative analysis of helium in pure bcc metals. Complementary post-implantation annealing treatments are carried out to characterize the 4He-depth profile evolution.