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Characterization of the Photo-Alignment Material SD-1/SDA-2 with Spectroscopic Ellipsometry
Dalarna University.
Laboratory of Applied Optics, IFM, Linköping University.
Hong Kong University of Science and Technology, Kowloon, Hong Kong.
Hong Kong University of Science and Technology, Kowloon, Hong Kong.
2007 (English)In: Proceedings of the IDW'07, Japan, 2007, 391-394 p.Conference paper (Refereed)
Abstract [en]

Variable angle spectroscopic ellipsometry (VASE) is applied for investigation of the azo-dye SD-1/SD-2 which are used for photoalignment of liquid crystals. The azo-dye was spin coated on silicon substrates. Samples as prepared as well as samples illuminated with polarized UV light were studied. The measured optical constants were modelled with an ensample of the Lorentz oscillators. The results confirm the reorientation mechanism of the photo-induced order formation in the azo-dye films under the action of polarized light, and also show that there exist some photochemical processes.

Place, publisher, year, edition, pages
2007. 391-394 p.
Keyword [en]
generalized ellipsometry, photo-alignment, liquid crystal
URN: urn:nbn:se:uu:diva-107452OAI: oai:DiVA.org:uu-107452DiVA: diva2:229376
Available from: 2009-08-12 Created: 2009-08-12 Last updated: 2009-08-13
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.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 664
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
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)
Available from: 2009-09-03 Created: 2009-08-11 Last updated: 2009-09-03Bibliographically approved

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