Fabrication and optical conductivities of strained epitaxial Na{sub x}CoO{sub 2} thin films: x=0.5, 0.7

Journal Article · Fri Aug 15 04:00:00 EDT 2008 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2008.05.005· OSTI ID:21128405

Son, J Y; Shin, Y H ^[1]

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1. Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784 (Korea, Republic of)

Epitaxial {gamma} phase-Na{sub x}CoO{sub 2} thin films were deposited on (001) sapphire by the pulsed laser deposition method. To fabricate epitaxial Na{sub 0.5}CoO{sub 2} thin films, we used a solution of iodine-dissolved acetonitrile and obtained an epitaxial Na{sub 0.5}CoO{sub 2} thin film with a high crystallinity because of Na deintercalation of epitaxial Na{sub 0.7}CoO{sub 2}. From the spectroscopic ellipsometry analysis, we obtained the optical constants as well as the optical conductivities for the Na{sub 0.5}CoO{sub 2} and Na{sub 0.7}CoO{sub 2} thin films. The energy splitting between e{sub g} and a{sub 1g} increased because of the structural strain of the Na{sub 0.7}CoO{sub 2} thin film. It is inferred that the structural strain is the source for the lower resistivity and the preservation of the strongly correlated system up to 200 K for the Na{sub 0.7}CoO{sub 2} thin film. On the other hand, the strain in the Na{sub 0.5}CoO{sub 2} thin film was not affected, and the charge-ordering state and the Na content (x=0.5) only cause the charge-ordering state. - Graphical abstract: From the spectroscopic ellipsometry analysis, we obtained optical constants as well as optical conductivities for Na{sub 0.5}CoO{sub 2} and Na{sub 0.7}CoO{sub 2} thin films. The energy splitting between e{sub g} and a{sub 1g} increased as a result of the structural strain of the Na{sub 0.7}CoO{sub 2} thin film.

• OSTI ID: 21128405
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 8 Vol. 181; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ACETONITRILE
COBALT COMPOUNDS
ELLIPSOMETRY
ENERGY BEAM DEPOSITION
EPITAXY
FABRICATION
IODINE
LASER RADIATION
OXIDES
PULSED IRRADIATION
SAPPHIRE
SODIUM COMPOUNDS
STRAINS
THIN FILMS