Browsing by Author "Dimitrov, D. Z."

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Atomic layer deposition prepared Al-doped ZnO for liquid crystal displays applications
(2018-05-01)
Su, Y. C.
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Chiou, C. C.
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Marinova, V.
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Lin, S. H.
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Bozhinov, N.
Aluminum-doped zinc oxide (AZO) layers are prepared by using atomic layer deposition technique. The obtained layers possess high optical transmittance at visible and near-infrared spectral range. By varying the Al content, optimal growth compositions of AZO are established where the electrical conductivity of the film is highest. Based on performed optical and electrical characteristics measurements, selected AZO films with optimal conductivity are implemented as transparent electrodes in liquid crystal display devices. The electro-optical modulation characteristics of these devices are found to be comparable to those of devices using commercial ITO electrodes.
FLEXIBLE AND STRETCHABLE OPTOELECTRONIC DEVICES USING GRAPHENE
(2019-01-01)
Chiou, Chung Chin
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Marinova, Vera
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Petrov, Stefan
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Fidanova, Cvetelina
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Angelova, Ina
In this paper we demonstrate flexible polymer dispersed liquid crystal (PDLC) devices using graphene as transparent conductive electrodes on polyethylene terephthalate (PET) substrate. Graphene was grown by Low Pressure Chemical Vapor Deposition (LPCVD) technique and characterized by Raman analysis, optical and electrical measurements. Several graphene-based PDLC devices have been fabricated and their electro-optical characteristics, response time and bending ability were measured and discussed. The results support the graphene promising features for integration in flexible optoelectronics.
Growth and characterization of LuVO4 single crystals
(2017-09-01)
Dimitrov, D. Z.
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Rafailov, P. M.
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Chen, Y. F.
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Lee, C. S.
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Todorov, R.
Large LuVO4 single crystals have been successfully obtained by high-temperature solution method. The structure details of these crystals are determined by X-ray crystallographic analysis and Raman spectroscopy. It is observed that the crystal consists of LuVO4 phase with trace amount of imperfections possibly due to oxygen vacancies. The optical quality of the crystal is assessed by Spectroscopic Ellipsometry (SE). The crystal shows higher than +0.2 birefringence in a large interval of wavelengths. (C) 2017 Elsevier B.V. All rights reserved.
Unusual rotating magnetocaloric effect in the hexagonal ErMnO3 single crystal
(2018-11-14)
Balli, M.
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Jandl, S.
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Fournier, P.
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Vermette, J.
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Dimitrov, D. Z.
It is known that orthorhombic RMnO3 multiferroics (R = magneticrareearth) with low symmetry exhibit a large rotating magnetocaloric effect because of their strong magnetocrystalline anisotropy. In this paper, we demonstrate that the hexagonal ErMnO3 single crystals also unveil a giant rotating magnetocaloric effect that can be obtained by spinning them in constant magnetic fields around their a or b axes. When the ErMnO3 crystal is rotated with the magnetic field initially parallel to the c axis, the resulting entropy change reaches maximum values of 7, 17, and 20 J/kg K under 2, 5, and 7 T, respectively. These values are comparable to or even larger than those shown by some of the best orthorhombic phases. More interestingly, the generated anisotropic thermal effect is about three times larger than that exhibited by the hexagonal HoMnO3 single crystal. The enhancement of the rotating magnetocaloric effect in the hexagonal ErMnO3 compound arises from the unique features of the Er3+ magnetic sublattice. In fact, the Er3+ magnetic moments located at 2a sites experience a first-order metamagnetic transition close to 3 K along the c axis resulting in a peaked magnetocaloric effect over a narrower temperature range. In contrast, the "paramagnetic" behavior of Er3+ magnetic moments within the ab plane produces a larger magnetocaloric effect over a wider temperature range. Therefore, the magnetocaloric effect anisotropy is maximized between the c and the ab directions, leading to a giant rotating magnetocaloric effect.