Selective Chemical Etching of Latent Compositional Microstructures in Sputtered Co-Cr Films

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Abstract
We examine the validity of a chemical etching method to reveal latent compositional microstructures in a sputtered Co-19.7 at% Cr film. Using dilute aqua regia as the etching solution, changes in the microstructure, composition and chemical state of Co and Cr through chemical etching are investigated. It is observed that the chemical etching progresses from the film surface towards the bottom, revealing an in-grain microstructure comprising periodic stripes (about 8-nm periodicity). The etching causes an increase in Cr and O content and the preferential formation of Cr oxide. These results suggest that the latent compositional microstructure is revealed by selective chemical etching due to the passivation of Cr-rich regions resulting in the preferential dissolution of Co-rich regions.