Hydrogen superpermeation resistant to ion sputtering

Abstract

A nonmetallic monolayer on the surface of a metallic membrane gives rise to the superpermeation of suprathermal hydrogen. This means that virtually the whole implanted flux passes through the membrane, depending neither on membrane temperature nor on its thickness. The fact that superpermeation is degrading at a sufficiently high energy of the incident hydrogen particles was considered to be a ‘natural’ result of sputtering of the monolayer. This view was equally applied to Nb, one of the best metals for superpermeation. It is shown in this article that Nb containing O impurity will be normally superpermeable to suprathermal hydrogen at any incident energy, the earlier observed sensitivity to sputtering being conditioned by the NbC layer originally present at the ‘real’ Nb surface. The dynamic exchange between the surface and bulk O impurity is proven to be responsible for the superpermeability of Nb resistant to sputtering. When the NbC layer is present, it hinders such an exchange.