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Issue 83, 2016
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Spectroscopic ellipsometry for compositionally induced bandgap tuning of combinatorial niobium–tantalum anodic oxides

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Abstract

Variable angle spectroscopic ellipsometry (VASE) was used for optical property mapping of anodic oxides grown on a wide spread Nb–Ta thin film combinatorial library (Nb content ranging between 8 and 84 at%) with 2 at% resolution. The microstructure of the parent metal alloys was tuned by modifying the library deposition conditions in order to avoid compositionally induced microstructure dissimilarities between the alloys. This allowed an interpretation of the mixed oxides properties based on a single Tauc–Lorentz oscillator for data fitting. Upon anodization up to 10 V vs. SHE, VASE was used to fit the oxide thickness in order to map the oxide formation factors with the results showing a good agreement with the electrochemical data. The measured bandgap values of the Nb–Ta oxides show a deviation from the linear model based on mixing individual Nb and Ta electronegativities proportional to their atomic fractions. This behavior was explained via an in-depth compositional gradient in the oxides. Minority species are depleted at the metal/oxide interface triggering a non-linear shift in the resulting alloy electronegativity. The Nb–Ta mixed oxides bandgap tuning via compositional tuning of the parent metal has been demonstrated and absorption close to the edge of the visible spectrum was identified above 30 at% Nb.

Graphical abstract: Spectroscopic ellipsometry for compositionally induced bandgap tuning of combinatorial niobium–tantalum anodic oxides

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Publication details

The article was received on 20 May 2016, accepted on 07 Aug 2016 and first published on 08 Aug 2016


Article type: Paper
DOI: 10.1039/C6RA13157C
Citation: RSC Adv., 2016,6, 79934-79942
  • Open access: Creative Commons BY-NC license
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    Spectroscopic ellipsometry for compositionally induced bandgap tuning of combinatorial niobium–tantalum anodic oxides

    W. Limberger, C. C. Mardare, C. Cobet, J. Zuo, A. W. Hassel and A. I. Mardare, RSC Adv., 2016, 6, 79934
    DOI: 10.1039/C6RA13157C

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