Electrochemistry on binary valve metal combinatorial libraries: niobium-tantalum thin films

• A Nb-Ta wide spread (89 at.%) co-sputtered thin film library was characterized.
• Microstructure and crystallography of Nb-Ta alloys were mapped along the composition.
• Scanning droplet cell microscopy was used for mapping of electrochemical properties.
• Oxide growth (<2.6 nm/V) and dielectric constants (<50) were analyzed for each alloy.
• Type n semiconducting behavior was found and mixed oxide composition was analyzed.

A Nb-Ta thin film compositional spread obtained from a co-sputtering process was analysed. The microstructure and crystallographic investigations revealed the presence of a compositional threshold at Nb-60 at.%Ta where the change from tetragonal to cubic symmetry was evidenced by a mixed tetragonal-cubic phase. The electrochemical properties of the anodic oxides were studied via cyclic voltammetry and the oxide formation factors were mapped along the entire compositional spread. Values ranging from 1.8 nm·V−1 at the Ta-rich side to 2.6 nm·V−1 at the Nb-rich side of the library were measured. All Nb-Ta mixed anodic oxides were found to exhibit a type-n semiconducting behaviour as evidenced by Mott-Schottky analysis. The chemical composition of the surface anodic oxides differed from the composition of the parent metal alloys and no clear trend could be identified regarding their mismatch.

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