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

Published online by Cambridge University Press:  26 July 2012

Rong Huang ,
Teruyasu Mizoguchi ,
Kenji Sugiura ,
Shin-ichi Nakagawa ,
Hiromichi Ohta ,
Tomohiro Saito ,
Kunihito Koumoto ,
Tsukasa Hirayama  and
Yuichi Ikuhara
Rong Huang*
Affiliation:
Nanostructures Research Laboratory, Japan Fine Ceramics Center, Atsuta, Nagoya 456-8587, Japan
Teruyasu Mizoguchi
Affiliation:
Institute of Engineering Innovation, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
Kenji Sugiura
Affiliation:
Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan
Shin-ichi Nakagawa
Affiliation:
Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan
Hiromichi Ohta
Affiliation:
Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan
Tomohiro Saito
Affiliation:
Nanostructures Research Laboratory, Japan Fine Ceramics Center, Atsuta, Nagoya 456-8587, Japan
Kunihito Koumoto
Affiliation:
Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan
Tsukasa Hirayama
Affiliation:
Nanostructures Research Laboratory, Japan Fine Ceramics Center, Atsuta, Nagoya 456-8587, Japan
Yuichi Ikuhara
Affiliation:
Nanostructures Research Laboratory, Japan Fine Ceramics Center, Atsuta, Nagoya 456-8587, Japan; and Institute of Engineering Innovation, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
*
a) Address all correspondence to this author. e-mail: [email protected]
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Abstract

Microstructures of epitaxial Ca0.33CoO2 thin films, which were grown on m 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 Ca0.33CoO2 thin film and substrate are and , having an angle of about 43° with for the film deposited on m plane, and and 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.

Keywords

FilmMicrostructureScanning transmission electron microscopy (STEM)
Type
Articles
Information
Journal of Materials Research , Volume 24 , Issue 1 , January 2009 , pp. 279 - 287
Copyright
Copyright © Materials Research Society 2009

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