Flash electropolishing of TEM lamellas of irradiated tungsten

Abstract

The study in the transmission electron microscopy (TEM) of the irradiation-induced microstructure of tungsten, a material promising for its applications at high temperatures in harsh radiation environments, is rendered difficult by the high level of radioactivity. To circumvent this problem, it is nowadays a routine to reduce the TEM sample size with the focused ion beam (FIB) technique. In this way, one extracts an electron transparent thin lamella that is only a few microns in size. However, FIB induces additional radiation damage in the surface layer, which has to be removed by the so-called flash polishing technique in order to detect the initial damage structure in an irradiated sample. In this study, we evaluate the technique of flash electropolishing in an aqueous solution of NaOH as a method to remove this surface damage from tungsten lamella samples. The conditions of flash electropolishing are optimized as a function of temperature, voltage, FIB grid and weld material. Anisotropic etching dependence on the crystallographic direction was evaluated, with the highest polishing resistance in the region between (5 2 1) and (1 1 0).