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Spectroscopic ellipsometry characterization of electrochromic tungsten oxide and nickel oxide thin films made by sputter deposition
Department of Material Science, Dalarna University.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Laboratory of Applied Optics, Department of Physics, Chemistry and Biology, Linköping University.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.ORCID iD: 0000-0002-8279-5163
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2010 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 94, no 5, 724-732 p.Article in journal (Refereed) Published
Abstract [en]

Electrochromic films of tungsten oxide and nickel oxide were made by reactive dc magnetron sputtering and were characterized by X-ray diffraction, Rutherford backscattering spectrometry, scanning electron microscopy, and atomic force microscopy. The optical properties were investigated in detail by spectroscopic ellipsometry and spectrophotometry, using a multiple-sample approach. The W oxide film was modeled as a homogeneous isotropic layer, whereas the Ni oxide film was modeled as an anisotropic layer with the optical axis perpendicular to the surface. Parametric models of the two layers were then used to derive complex refractive index in the 300-1700-nm-range, film thickness, and surface roughness. A band gap of 3.15 eV was found for the W oxide film, using a Tauc-Lorentz parameterization. For the Ni oxide film, taken to have direct optical transitions, band gaps along the optical axis, perpendicular to it, and in an isotropic intermediate layer at the bottom of the film were found to be 3.95, 3.97, and 3.63 eV, respectively. Parameterization for the Ni oxide was made by use of the Lorentz model.

Place, publisher, year, edition, pages
2010. Vol. 94, no 5, 724-732 p.
Keyword [en]
ellipsometry, electrochromic, tungsten oxide, nickel oxide
National Category
Physical Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
URN: urn:nbn:se:uu:diva-107448DOI: 10.1016/j.solmat.2009.12.011ISI: 000277353900004OAI: oai:DiVA.org:uu-107448DiVA: diva2:229349
Available from: 2011-09-21 Created: 2009-08-12 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Optical Characterization and Optimization of Display Components: Some Applications to Liquid-Crystal-Based and Electrochromics-Based Devices
Open this publication in new window or tab >>Optical Characterization and Optimization of Display Components: Some Applications to Liquid-Crystal-Based and Electrochromics-Based Devices
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This dissertation is focused on theoretical and experimental studies of optical properties of materials and multilayer structures composing liquid crystal displays (LCDs) and electrochromic (EC) devices.

By applying spectroscopic ellipsometry, we have determined the optical constants of thin films of electrochromic tungsten oxide (WOx) and nickel oxide (NiOy), the films’ thickness and roughness. These films, which were obtained at spattering conditions possess high transmittance that is important for achieving good visibility and high contrast in an EC device.

Another application of the general spectroscopic ellipsometry relates to the study of a photo-alignment layer of a mixture of azo-dyes SD-1 and SDA-2. We have found the optical constants of this mixture before and after illuminating it by polarized UV light. The results obtained confirm the diffusion model to explain the formation of the photo-induced order in azo-dye films.

We have developed new techniques for fast characterization of twisted nematic LC cells in transmissive and reflective modes. Our techniques are based on the characteristics functions that we have introduced for determination of parameters of non-uniform birefringent media. These characteristic functions are found by simple procedures and can be utilised for simultaneous determination of retardation, its wavelength dispersion, and twist angle, as well as for solving associated optimization problems.

Cholesteric LCD that possesses some unique properties, such as bistability and good selective scattering, however, has a disadvantage – relatively high driving voltage (tens of volts). The way we propose to reduce the driving voltage consists of applying a stack of thin (~1µm) LC layers.

We have studied the ability of a layer of a surface stabilized ferroelectric liquid crystal coupled with several retardation plates for birefringent color generation. We have demonstrated that in order to accomplish good color characteristics and high brightness of the display, one or two retardation plates are sufficient.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 64 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 664
Keyword
ellipsometry, liquid crystal, LCD, optical anizotropy, electrochromic, inverse problems
National Category
Atom and Molecular Physics and Optics Atom and Molecular Physics and Optics Computational Mathematics
Research subject
Solid State Physics; Information Systems
Identifiers
urn:nbn:se:uu:diva-107429 (URN)978-91-554-7583-3 (ISBN)
Public defence
2009-09-24, 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
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Supervisors
Available from: 2009-09-03 Created: 2009-08-11 Last updated: 2009-09-03Bibliographically approved

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