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Polaron Absorption in Amorphous Tungsten Oxide Films
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.ORCID iD: 0000-0002-8279-5163
2001 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 90, 1860-1863 p.Article in journal (Refereed) Published
Abstract [en]

Amorphous thin films of tungsten oxide were deposited by sputtering onto glass substrates covered by conductive indium–tin oxide. The density and stoichiometry were determined by Rutherford backscattering spectrometry. Lithium ions were intercalated electrochemically into the films. The optical reflectance and transmittance were measured in the wavelength range from 0.3 to 2.5 μm, at a number of intercalation levels. The polaron absorption peak becomes more symmetric and shifts to higher energies until an intercalation level of 0.25 to 0.3 Li+/W, where a saturation occurs. The shape of the polaron peak is in very good agreement with the theory of Bryksin [Fiz. Tverd. Tela 24, 1110 (1982)]. Within this model, the shift of the absorption peak is interpreted as an increase in the Fermi level of the material as more Li ions are inserted.

Place, publisher, year, edition, pages
2001. Vol. 90, 1860-1863 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-92421DOI: 10.1063/1.1384853OAI: oai:DiVA.org:uu-92421DiVA: diva2:165491
Available from: 2004-11-12 Created: 2004-11-12 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Optical Absorption and Electrical Conductivity in Lithium Intercalated Amorphous Tungsten Oxide Films
Open this publication in new window or tab >>Optical Absorption and Electrical Conductivity in Lithium Intercalated Amorphous Tungsten Oxide Films
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Optical and electrical properties of electrochemically lithium ion intercalated thin films of x-ray amorphous tungsten oxide made by magnetron sputtering on glass substrates coated with a thin layer of conductive tin doped indium oxide, have been studied.

The composition and the density of the films were characterized by the ion beam analysis methods Rutherford Backscattering Spectroscopy and Elastic Recoil Detection Analysis.

The optical properties, transmittance and reflectance were investigated by spectophotometry in the wavelength range 300-2500 nm. The absorption coefficients were calculated at different lithium intercalation levels.

It was found that the absorption coefficient in an as-deposited blue film has a similar asymmetric shape as for films intercalated to a Li/W ratio of ~0.03. It was possible to electrochemically bleach this film to transparency. Stoichiometric films show optical irreversibility between the bleached and the colored state in the first cycle.

A polaron absorption model has been compared to the absorption coefficient for films of different intercalation levels. An increase in the Fermi level and in the polaron band width, and a nearly constant activation energy was found as the Li/W value increased. The radius of the polaron wavefunction for different lithium intercalation levels and film compositions has been estimated from electrical measurements.

The total absorption coefficient has been compared to the site-saturation model. The model is good for films intercalated in the optically reversible region. A modified site-saturation model that could be applied also in the optically irreversible region and involves electron transitions between W6+, W5+ and W4+ sites, has also been compared to experimental values.

It was found that the total absorption, optical density and the coloration efficiency is higher for the WO2.63 film than in the less oxygen deficient films and that this film is optically more durable in an electrochemically cyclic lifetime device test.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 73 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1045
Keyword
Technology, Lithium intercalation, amorphous, tungsten-oxide, sputtered films, optical absorption, polaron radius., TEKNIKVETENSKAP
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-4687 (URN)91-554-6106-9 (ISBN)
Public defence
2004-12-03, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2004-11-12 Created: 2004-11-12 Last updated: 2009-03-27Bibliographically approved

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Niklasson, Gunnar A.

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