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  • 1.
    Valyukh, Iryna
    Dalarna University, School of Technology and Business Studies, Materials Technology. Uppsala universitet, Institutionen för teknikvetenskaper.
    Optical Characterization and Optimization of Display Components: Some Applications to Liquid-Crystal-Based and Electrochromics-Based Devices2009Doctoral 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.

  • 2.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Arwin, Hans
    Chigrinov, Vladimir
    Valyukh, Sergiy
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Characterization of the photo-alignment material SD-1/SDA-2 with spectroscopic ellipsometry2007In: IDW '07: Proceedings of the 14th International Display Workshops, vols 1-3, 2007, Vol. 1-3, p. 391-394Conference paper (Refereed)
    Abstract [en]

    Variable angle spectroscopic ellipsometry (VASE) is applied for investigation of the azo-dye SD-1/SDA-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 ensemble 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.

  • 3.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Arwin, Hans
    Chigrinov, Vladimir
    Valyukh, Sergiy
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    UV-induced in-plane anisotropy in layers of mixture of the azo-dyes SD-1/SDA-2 characterized by spectroscopic ellipsometry2008In: Physica Status Solidi C - Current topics in solid state physics, vol.5, no.5, 2008, Vol. 5, no 5, p. 1274-1277Conference paper (Refereed)
    Abstract [en]

    The optical properties of the azo-dyes SD-1/SDA-2, which are used for photoaligning of liquid crystals (LCs), are investigated with Variable Angle Spectroscopic Ellipsometry (VASE). Films of mixture of SD-1/SDA-2 are deposited by spin coating on silicon wafers. The estimated thickness is approximately 10 nm. To achieve photo-induced anisotropy, one of the samples is illuminated during 15 minutes with linearly polarized UV light followed by thermal stabilization during 1 hour at 150 degrees C. VASE measurements are performed in the wavelength range 200-1350 rim at several angles of incidence and at different sample orientations. Dielectric functions of azo-dye films without/with polarized UV light illumination were modelled using an ensemble of Lorentz oscillators. The results confirm the diffusion model proposed recently for explanation of the formation of the photo-induced order in azo-dye films under the action of polarized light. Refractive indices, their wavelength dispersion and thicknesses of films of SD-1/SDA-2 are reported here.

  • 4.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Green, S.
    Arwin, H.
    Niklasson, G. A.
    Wäckelgård, Ewa
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Granqvist, C. G.
    Spectroscopic ellipsometry characterization of electrochromic tungsten oxide and nickel oxide thin films made by sputter deposition2010In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 94, no 5, p. 724-732Article in journal (Refereed)
    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. (C) 2009 Elsevier B.V. All rights reserved.

  • 5.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Slobodyanyuk, A
    Valyukh, S
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Using the Jones matrix for simulation of light propagation in anisotropic media2003In: Journal of optical technology (Print), ISSN 1070-9762, E-ISSN 1091-0786, Vol. 70, no 7, p. 470-473Article in journal (Refereed)
  • 6.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Slobodyanyuk, A.
    Valyukh, S.
    Sorokin, V.
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    On accuracy of the Jones matrix method for simulation of light propagation in twisted nematic liquid crystals2002In: Proc. of the 11th Int. Symp. Advanced Display Technologies, UkraineArticle in journal (Refereed)
  • 7.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Slobodyanyuk, A.
    Valyukh, S.
    Sorokin, V.
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Simulation of light scattered by reflective polarizer with a rough metallic surface2002In: Eurodisplay 2002, Nice, France, 2002Conference paper (Refereed)
  • 8.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Valyukh, S.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Theoretical study of the optical properties of low voltage stacked cholesteric liquid-crystal displays2004In: Asia display, 2004Conference paper (Refereed)
  • 9.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Valyukh, Sergiy
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Arwin, H.
    Chigrinov, V.
    Characteristic functions for uniformly twisted birefringent media2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, no 6, article id 063110Article in journal (Refereed)
    Abstract [en]

    We present two functions for characterization of birefringent media with application to twisted nematic liquid crystal (LC) cells in the field off state. The first function is for reflective LC cells and the second is for transmissive LC cells. Based on the Stockes formalism, it is shown that these functions describe the ability of a layer of the twisted birefringent medium to change polarization of the output light and are invariant to the layer orientation. The characteristic functions are found in simple procedures and can be used for simultaneous determination of retardation, its wavelength dispersion, and twist angle, as well as for solving optimization problems. © 2007 American Institute of Physics.

  • 10.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Valyukh, Sergiy
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Skarp, Kent
    Chigrinov, V.
    Monochromatic bistable reflective and transfiective ferroelectric LCDs2005In: Proceedings of the 25th International Display Research Conference, Eurodisplay 2005, 2005, p. 305-308Conference paper (Refereed)
    Abstract [en]

    We study single and double polarizer monochromatic bistable reflective and transfective direct view ferroelectric liquid crystal displays (FLCDs). Three types of monochromatic displays are considered Black & White, Black & Yellow, Black & Green. Theoretical approach for finding optimal parameters of an FLCD is presented.

  • 11.
    Valyukh, Sergiy
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Valyuhk, Iryna
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Characterization of flexible reflective liquid crystal cells2005In: Journal of the Society for Information Display, ISSN 1071-0922, E-ISSN 1938-3657, Vol. 13, no 6, p. 501-506Article in journal (Refereed)
    Abstract [en]

    We consider peculiarities in testing flexible reflective liquid-crystal (LC) cells. Several new methods for measuring optical retardation of filled reflective LC cells on plastic substrates are proposed. Cases when the plastic is anisotropic and the LC cell consists of either one or two internal polarizers are studied. The majority of proposed methods can be applied for transmissive LC cells as well as for measuring twist angle.

  • 12.
    Valyukh, Sergiy
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Valyuhk, Iryna
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Spectrophotometric determination of reflective liquid crystal cell parameters2006In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 99, no 5Article in journal (Refereed)
    Abstract [en]

    We introduce a method for the determination of the optical retardation, its wavelength dispersion, the cell twist angle, and the orientation of the input director in a reflective liquid crystal (LC) cell. These parameters are found from the extremes of a characteristic function defined as a sum of two spectral reflectivities of the LC cell placed between a pair of linear polarizers. The reflectivities are measured for two cell orientations, one of which is arbitrary and the other one is turned through 45°. Both theoretical analysis and experimental procedures are presented. Excellent agreement between the experiment and our theory has been found. The proposed method can be applied to the measurement of reflective LC cells with small and large cell gaps, as well as cells with small and large twist angles.

  • 13.
    Valyukh, Sergiy
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Valyukh, Iryna
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Adås, C.
    Chigrinov, V.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Reflective liquid crystal cell parameters2004In: Asia display, 2004Conference paper (Refereed)
  • 14.
    Valyukh, Sergiy
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Valyukh, Iryna
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Xu, Peizhi
    Chigrinov, Vladimir
    Study on birefringent color generation for a reflective ferroelectric liquid crystal display2006In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 45, no 10A, p. 7819-7826Article in journal (Refereed)
    Abstract [en]

    We study the possibility of a layer of a surface stabilized ferroelectric liquid crystal coupled with several retardation plates for birefringent color generation. Double and single polarizer reflective bistable dichromatic ferroelectric liquid crystal displays are considered. We demonstrate that one or two retardation plates are sufficient for a display having good color characteristics and high brightness. Optimal parameters for green/red and blue/yellow ferroelectric liquid crystal displays are found.

1 - 14 of 14
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