Point-defect engineering of MoN/TaN superlattice films: A first-principles and experimental study

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Authors

KOUTNÁ Nikola HAHN R. ZÁLEŠÁK Jakub FRIÁK Martin BARTOSIK M. KECKES J. ŠOB Mojmír MAYRHOFER PH HOLEC David

Year of publication 2020
Type Article in Periodical
Magazine / Source MATERIALS & DESIGN
MU Faculty or unit

Faculty of Science

Citation
Web https://www.sciencedirect.com/science/article/pii/S0264127519306495?via%3Dihub
Doi http://dx.doi.org/10.1016/j.matdes.2019.108211
Keywords Superlattices; Vacancies; Ab initio; Metastable phases; XRD; EDX
Description Superlattice architecture represents an effective strategy to improve performance of hard protective coatings. Our model system, MoN/TaN, combines materials well-known for their high ductility as well as a strong driving force for vacancies. In this work, we reveal and interpret peculiar structure-stability-elasticity relations for MoN/TaN combining modelling and experimental approaches. Chemistry of the most stable structural variants depending on various deposition conditions is predicted by Density Functional Theory calculations using the concept of chemical potential. Importantly, no stability region exists for the defect-free superlattice. The X-ray Diffraction and Energy-dispersive X-ray Spectroscopy experiments show that MoN/TaN superlattices consist of distorted fcc building blocks and contain non-metallic vacancies in MoN layers, which perfectly agrees with our theoretical model for these particular deposition conditions. The vibrational spectra analysis together with the close overlap between the experimental indentation modulus and the calculated Young's modulus points towards MoN0.5/TaN as the most likely chemistry of our coatings.
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