Texture and interface characterization of iridium thin films grown on MgO substrates with different orientations
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Iridium thin films are grown by direct-current plasma magnetron sputtering, on MgO single-crystal substrates with various surface orientations, i.e. (100), (111), and (110). The surface morphology, the crystalline properties of the films, and the substrate–thin-film interface are investigated by atomic force microscopy, X-ray diffraction (XRD), focused ion beam scanning electron microscopy, and high-resolution transmission electron microscopy, respectively. The results reveal that hetero-epitaxial thin films with different crystallographic orientation and notable atomic scale smooth surface are obtained. From the XRD analysis, the following epitaxial relations are obtained: (1) (100)Ir||(100)MgO out-of-plane and Ir||MgO in-plane for Ir grown on MgO(100), (2) (110)Ir||(110)MgO out-of-plane and [1-10]Ir||[1-10]MgO in-plane for Ir grown on MgO(110), and (3) (111)Ir||(111)MgO out-of-plane and two variants for in-plane orientation [1-10]Ir||[1-10]MgO and [1-10]Ir||[10-1]MgO, respectively, for Ir grown on MgO(111). Because of the large misfit strain (9.7%), the thin films are found to grow in a strain-relaxed state with the formation of geometrical misfit dislocations with a ~ 2.8-nm spacing, whereas thermal strain is stored upon cooling down from the growth temperature (600 °C). The best structural characteristics are obtained for the (111)-oriented films with a mosaicity of 0.3° and vanishingly small lattice distortions. The (100)- and (110)-oriented films exhibit mosaicities of ~ 1.2° and lattice distortions of ~ 1% which can be explained by the larger surface energy of these planes as compared to (111).
This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CCCDI—UEFISCDI project number 61/2016 within PNCDI III, Core Program PN19-03 (Contract No. 21N/08.02.2019) and by the H2020 European project “MASTERS” within the M-ERA.NET call (http://www.unilim.fr/h2020_masters). The authors gratefully acknowledge the help of Pierre CARLES and thank the CARMALIM team at the “Centre Européen de la Céramique” in Limoges, for their support in investigating the structure and morphology of the thin-film samples.
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