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Ellipsometrically determined optical properties of nickel-containing tungsten oxide thin films: Nanostructure inferred from effective medium theory
Laboratory of Applied Optics, Dept of Physics, Chemistry and Biology, Linköping University.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
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2012 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 4, 044308- p.Article in journal (Refereed) Published
Abstract [en]

Films of NixW1−x oxide with 0.05 ≤ x ≤ 0.53 were produced by reactive dc magnetron co-sputtering onto Si. Such films have documented electrochromism. Spectroscopic ellipsometry was used to extract accurate data on the dielectric function in the photon range 0.062 to 5.62 eV. The results for 0.62 to 5.62 eV were compared with computations from the Bruggeman effective medium theory applied to two nanostructural models: one representing a random mixture of structural entities characterized by the dielectric functions of WO3 and NiWO4 and the other describing a random mixture of WO3 and NiO. Unambiguous evidence was found in favor of the former model, and hence the films are composed of nanosized tungsten oxide and nickel tungstate. This agrees excellently with an earlier investigation of ours on NixW1−x oxide films, where nanostructure was inferred from Raman spectroscopy, x-ray photoelectron spectroscopy, and x-ray diffraction.

Place, publisher, year, edition, pages
2012. Vol. 112, no 4, 044308- p.
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
URN: urn:nbn:se:uu:diva-179762DOI: 10.1063/1.4748166ISI: 000308410100079OAI: oai:DiVA.org:uu-179762DiVA: diva2:546155
Available from: 2012-08-22 Created: 2012-08-22 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Electrochromic Nickel – Tungsten Oxides: Optical, Electrochemical and Structural Characterization of Sputter-deposited Thin Films in the Whole Composition Range
Open this publication in new window or tab >>Electrochromic Nickel – Tungsten Oxides: Optical, Electrochemical and Structural Characterization of Sputter-deposited Thin Films in the Whole Composition Range
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates the electrochromic NixW1-x oxide thin film system, where 0 < x < 1. The thin films were deposited by reactive DC magnetron co-sputtering from one Ni and one W metal target. In addition, Ni oxide was deposited with water vapor added to the sputtering gas. The different compositions were structurally characterized by X-ray diffraction, X-ray photoelectron-, Rutherford backscattering- and Raman spectroscopy. Possible nanostructures were studied by ellipsometry together with effective medium theory. Optical and electrochemical properties were investigated by spectrophotometry and cyclic voltammetry in 1 M lithium perchlorate in propylene carbonate (Li-PC). Li-PC electrolyte was used as it is being compatible with both W and Ni oxides. Few studies have previously been made on Ni oxides in Li-PC.

Films with high Ni content, 0.85 < x < 1, were polycrystalline and all other films were amorphous. W-rich films, x < 0.5, consisted of a mixture of W oxide and NiWO4 -phases, and the Ni-rich samples, x > 0.5, probably consisted of hydrated Ni oxide and NiWO4 -phases. Films with 0 < x < 0.3 showed electrochromic properties similar to W oxide, and films with 0.7 < x < 1 behaved as Ni oxide. For 0.4 < x < 0.7 no optical change was seen. At the border of cathodic electrochromic and non-electrochromic behavior, i.e. x ~ 0.4, the sample behaved as an optically passive intercalation material. The transmittance change was 0.45 and 0.15 for the W-rich and Ni-rich films, respectively. Ni addition to W oxide improved the coloration efficiency. For the Ni-rich films the charge insertion/extraction and optical modulation was low and an aging effect resulted in strong bleaching of the samples. The advantage of W addition to Ni oxide was that the transparency at the bleached state was enhanced. Moreover, it was found that the hydrous character of the Ni oxide had a large impact on the electrochromic performance, both when electrochemically cycled in KOH and in the non-aqueous Li-PC.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 116 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 963
Keyword
Electrochromism, Nickel oxide, Tungsten oxide, Lithium intercalation, Sputtering, Thin films, Nanostructures, Optical properties
National Category
Materials Engineering
Research subject
Solid State Physics
Identifiers
urn:nbn:se:uu:diva-179764 (URN)978-91-554-8444-6 (ISBN)
Public defence
2012-10-12, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2012-09-21 Created: 2012-08-22 Last updated: 2013-01-22Bibliographically approved

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