du.sePublications
Change search
Link to record
Permanent link

Direct link
BETA
Alternative names
Publications (10 of 14) Show all publications
Valyukh, I., Green, S., Arwin, H., Niklasson, G. A., Wäckelgård, E. & Granqvist, C. G. (2010). Spectroscopic ellipsometry characterization of electrochromic tungsten oxide and nickel oxide thin films made by sputter deposition. Solar Energy Materials and Solar Cells, 94(5), 724-732
Open this publication in new window or tab >>Spectroscopic ellipsometry characterization of electrochromic tungsten oxide and nickel oxide thin films made by sputter deposition
Show others...
2010 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 94, no 5, p. 724-732Article 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. (C) 2009 Elsevier B.V. All rights reserved.

Keywords
Ellipsometry; Electrochromic; Tungsten oxide; Nickel oxide
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-10489 (URN)10.1016/j.solmat.2009.12.011 (DOI)000277353900004 ()
Available from: 2012-08-03 Created: 2012-08-03 Last updated: 2017-12-07Bibliographically approved
Valyukh, I. (2009). Optical Characterization and Optimization of Display Components: Some Applications to Liquid-Crystal-Based and Electrochromics-Based Devices. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
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. p. 64
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 664
Keywords
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
Identifiers
urn:nbn:se:du-18931 (URN)978-91-554-7583-3 (ISBN)
Public defence
2009-09-24, 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, 13:15 (English)
Opponent
Supervisors
Available from: 2015-07-29 Created: 2015-07-29 Last updated: 2015-07-29Bibliographically approved
Valyukh, I., Arwin, H., Chigrinov, V. & Valyukh, S. (2008). UV-induced in-plane anisotropy in layers of mixture of the azo-dyes SD-1/SDA-2 characterized by spectroscopic ellipsometry. In: Physica Status Solidi C - Current topics in solid state physics, vol.5, no.5: . Paper presented at 4th International Conference on Spectroscopic Ellipsometry (ICSE-4), JUN 11-15, 2007, Stockholm, SWEDEN (pp. 1274-1277). , 5(5)
Open this publication in new window or tab >>UV-induced in-plane anisotropy in layers of mixture of the azo-dyes SD-1/SDA-2 characterized by spectroscopic ellipsometry
2008 (English)In: Physica Status Solidi C - Current topics in solid state physics, vol.5, no.5, 2008, Vol. 5, no 5, p. 1274-1277Conference paper, Published 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.

National Category
Materials Engineering
Identifiers
urn:nbn:se:du-17683 (URN)10.1002/pssc.200777881 (DOI)000256862500066 ()
Conference
4th International Conference on Spectroscopic Ellipsometry (ICSE-4), JUN 11-15, 2007, Stockholm, SWEDEN
Available from: 2015-06-03 Created: 2015-06-03 Last updated: 2018-10-08Bibliographically approved
Valyukh, I., Valyukh, S., Arwin, H. & Chigrinov, V. (2007). Characteristic functions for uniformly twisted birefringent media. Journal of Applied Physics, 102(6), Article ID 063110.
Open this publication in new window or tab >>Characteristic functions for uniformly twisted birefringent media
2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, no 6, article id 063110Article in journal (Refereed) Published
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.

National Category
Materials Engineering
Identifiers
urn:nbn:se:du-18858 (URN)10.1063/1.2781300 (DOI)2-s2.0-34848921152 (Scopus ID)
Note

Export Date: 22 July 2015

Available from: 2015-07-28 Created: 2015-07-22 Last updated: 2018-10-08Bibliographically approved
Valyukh, I., Arwin, H., Chigrinov, V. & Valyukh, S. (2007). Characterization of the photo-alignment material SD-1/SDA-2 with spectroscopic ellipsometry. In: IDW '07: Proceedings of the 14th International Display Workshops, vols 1-3. Paper presented at 14th International Display Workshop, Sappora, Japan, December 5, 2007. (pp. 391-394). , 1-3
Open this publication in new window or tab >>Characterization of the photo-alignment material SD-1/SDA-2 with spectroscopic ellipsometry
2007 (English)In: IDW '07: Proceedings of the 14th International Display Workshops, vols 1-3, 2007, Vol. 1-3, p. 391-394Conference paper, Published 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.

National Category
Materials Engineering
Identifiers
urn:nbn:se:du-17637 (URN)000258483900096 ()
Conference
14th International Display Workshop, Sappora, Japan, December 5, 2007.
Available from: 2015-06-02 Created: 2015-06-01 Last updated: 2018-10-08Bibliographically approved
Valyukh, S., Valyuhk, I. & Skarp, K. (2006). Spectrophotometric determination of reflective liquid crystal cell parameters. Journal of applied physiology, 99(5)
Open this publication in new window or tab >>Spectrophotometric determination of reflective liquid crystal cell parameters
2006 (English)In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 99, no 5Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Institute of Physics, 2006
National Category
Materials Engineering
Identifiers
urn:nbn:se:du-1270 (URN)10.1063/1.2177376 (DOI)000236002900002 ()
Available from: 2005-07-01 Created: 2005-07-01 Last updated: 2018-10-08Bibliographically approved
Valyukh, S., Valyukh, I., Xu, P. & Chigrinov, V. (2006). Study on birefringent color generation for a reflective ferroelectric liquid crystal display. Japanese Journal of Applied Physics, 45(10A), 7819-7826
Open this publication in new window or tab >>Study on birefringent color generation for a reflective ferroelectric liquid crystal display
2006 (English)In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 45, no 10A, p. 7819-7826Article in journal (Refereed) Published
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.

Keywords
ferroelectric liquid crystal, reflective display, birefringent color generation, modeling, polarization interference filter
National Category
Materials Engineering
Identifiers
urn:nbn:se:du-17547 (URN)10.1143/JJAP.45.7819 (DOI)000241508600050 ()
Available from: 2015-05-29 Created: 2015-05-26 Last updated: 2018-10-08Bibliographically approved
Valyukh, S., Osterman, J., Valyuhk, I. & Skarp, K. (2005). Characterization of flexible reflective liquid crystal cells. Journal of the Society for Information Display, 13(6), 501-506
Open this publication in new window or tab >>Characterization of flexible reflective liquid crystal cells
2005 (English)In: Journal of the Society for Information Display, ISSN 1071-0922, E-ISSN 1938-3657, Vol. 13, no 6, p. 501-506Article in journal (Refereed) Published
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.

Keywords
reflective LCD; measuring of lCD; flexible LCD
National Category
Materials Engineering
Identifiers
urn:nbn:se:du-1273 (URN)10.1889/1.1974000 (DOI)000236279000008 ()
Available from: 2005-07-01 Created: 2005-07-01 Last updated: 2018-10-08Bibliographically approved
Valyukh, I., Valyukh, S., Skarp, K. & Chigrinov, V. (2005). Monochromatic bistable reflective and transfiective ferroelectric LCDs. In: Proceedings of the 25th International Display Research Conference, Eurodisplay 2005: . Paper presented at 25th International Display Research Conference, Edinburgh, Scotland, Sept. 19-22, 2005. (pp. 305-308).
Open this publication in new window or tab >>Monochromatic bistable reflective and transfiective ferroelectric LCDs
2005 (English)In: Proceedings of the 25th International Display Research Conference, Eurodisplay 2005, 2005, p. 305-308Conference paper, Published 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.

National Category
Materials Engineering
Identifiers
urn:nbn:se:du-17530 (URN)000258328800077 ()
Conference
25th International Display Research Conference, Edinburgh, Scotland, Sept. 19-22, 2005.
Available from: 2015-05-26 Created: 2015-05-25 Last updated: 2018-10-08Bibliographically approved
Valyukh, S., Valyukh, I., Adås, C., Chigrinov, V. & Skarp, K. (2004). Reflective liquid crystal cell parameters. In: Asia display: . Paper presented at Asia display, 2004.
Open this publication in new window or tab >>Reflective liquid crystal cell parameters
Show others...
2004 (English)In: Asia display, 2004Conference paper, Published paper (Refereed)
National Category
Materials Engineering
Identifiers
urn:nbn:se:du-1269 (URN)
Conference
Asia display, 2004
Available from: 2005-07-01 Created: 2005-07-01 Last updated: 2018-10-08Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5910-4355

Search in DiVA

Show all publications