Microstructure evolution of Ca0.33 CoO2 thin films investigated by high-angle annular dark-field scanning transmission electron microscopy

Rong Huang, Teruyasu Mizoguchi, Kenji Sugiura, Shin Ichi Nakagawa, Hiromichi Ohta, Tomohiro Saito, Kunihito Koumoto, Tsukasa Hirayama, Yuichi Ikuhara

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    4 Citations (Scopus)

    Abstract

    Microstructures of epitaxial Ca0.33 CoO2 thin films, which were grown on m(11̄00) plane and c(0001) plane of α-Al2O3 by the reactive solid-phase epitaxy (R-SPE) method and the subsequent ion-exchange treatment, were investigated in detail by using selected-area electron diffraction, high-resolution transmission electron microcopy, spherical-aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (Cs-corrected HAADF-STEM), and electron energy-loss spectroscopy (EELS). Detailed electron diffraction analyses reveal that the orientation relationships between Ca0.33 CoO2 thin film and substrate are [112̄0] Ca0.33 CoO2//[0001] Al2O3 and (0001)Ca0.33 CoO2, having an angle of about 43° with (1100)Al2O3 for the film deposited on m(11̄00) plane, and [11̄00] Ca0.33 CoO2//[112̄0] Al2O3 and (0001)Ca0.33 CoO2//(0001] Al2O3 for the film deposited on c(0001) plane though a Ca-Al-O amorphous layer formed between them. CoO seed layer near the interface and residual Co3O4 phase inside the films were observed and identified by HAADF-STEM and EELS in both samples. Such microstructural configuration indicates that the processes of film growth during R-SPE are (i) oxidation of CoO into Co3O4 with residual CoO layer near the interface and (ii) intercalation of Na+ layer into Co3O4 to achieve the layered NaxCoO2 film while forming Na-Al-O amorphous layer at the interface.

    Original languageEnglish
    Pages (from-to)279-287
    Number of pages9
    JournalJournal of Materials Research
    Volume24
    Issue number1
    DOIs
    Publication statusPublished - 2009 Jan 1

    ASJC Scopus subject areas

    • Materials Science(all)
    • Condensed Matter Physics
    • Mechanics of Materials
    • Mechanical Engineering

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  • Cite this

    Huang, R., Mizoguchi, T., Sugiura, K., Nakagawa, S. I., Ohta, H., Saito, T., Koumoto, K., Hirayama, T., & Ikuhara, Y. (2009). Microstructure evolution of Ca0.33 CoO2 thin films investigated by high-angle annular dark-field scanning transmission electron microscopy. Journal of Materials Research, 24(1), 279-287. https://doi.org/10.1557/jmr.2009.0020