Full elemental depth-profiling with nanoscale resolution: The potential of Elastic Recoil Detection (ERD) in membrane science

Abstract

Extensive characterization is needed to understand how the physicochemical properties of polymeric membranes are related to their transport properties and to allow optimization of membrane design. Currently, most techniques characterize the (near)-surface region of the membrane, even though its bulk obviously also plays a significant role in the final membrane performance. To achieve depth-profiles of the elemental composition of both integrally skinned asymmetric (ISA) and thin-film composite (TFC) membranes, elastic recoil detection (ERD), an ion beam analysis technique, is now introduced to the field as a potentially highly valuable tool to complement for instance XPS, EDX or RBS. The determination of the complete elemental composition, importantly also including hydrogen, as function of the membrane thickness allows to gain knowledge about its depth-heterogeneity at an impressive combination of ca. 15 nm resolution with ppm-range sensitivity. This very low detection limit additionally allows the analytical quantification of e.g. remnants from synthesis conditions. The potential as well as the pitfalls of ERD as a novel, valuable technique for membrane characterization are critically discussed and illustrated by the determination of the thickness of polyamide-based top-layers of TFC membranes.