Browsing by Author "Karashanova D."

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    DIELECTRIC PROPERTIES OF NEW COMPOSITES BASED ON GRAPHENE OXIDE AND NANO-SIZED ZnO
    (2021-01-01) Staneva A.; Martinov B.; Slavov S.; Karashanova D.; Mateeva J.; Melo B.M.G.; Costa L.C.
    The objectives of this study were to obtain a complete series of graphene oxide and nano sized zinc oxide and to make a structural and phase characterization of the resulting composites. XRD, SEM, EDX, TEM and impedance analyses were used to investigate these materials as energy storage devices. The complex dielectric permittivity was measured for all samples as a function of frequency. All dielectric characteristics were studied (frequencies from from 100 Hz to 1 MHz and temperatures from 150 to 400 K). The composite GO/ZnO - 80/20 is closer to the desired properties.
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    Photoinduced birefringence in azopolymer doped with Au nanoparticles
    (2019-10-08) Nazarova D.; Nedelchev L.; Stoykova E.; Blagoeva B.; Mateev G.; Karashanova D.; Georgieva B.; Kostadinova D.
    A study of the photoinduced birefringence in nanocomposite thin films of the azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt]) doped with gold (Au) nanoparticles (NPs) is presented. The NPs are with a spherical shape and mean size 10 nm. Transmission electron microscopy (TEM) and Dynamic Light Scattering (DLS) analyses of the particles have also been made. Samples were prepared with five different concentrations of the NPs in the azopolymer films varying from 0 (non-doped azopolymer film) to 4 a.u. (1 a.u. = 0.015 wt %). Birefringence was induced by a He-Cd laser with a wavelength 442 nm and measured with probe Diode Pumped Solid State (DPSS) laser at 635 nm. An increase of the photoinduced birefringence in doped azopolymer nanocomposite films compared to samples of undoped azopolymers was observed. The maximal enhancement was achieved for films with 2 a.u. of Au NPs.
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    Thin dye layers - Vacuum deposition and structure
    (2012-01-01) Dimov D.; Assa J.; Georgiev A.; Kazakov R.; Karashanova D.; Danev G.; Spassova E.
    Vacuum-deposited layers of zinc phthalocyanine and perylene-3,4,9,10- tetracarboxylic dianhydride were obtained with regard to the development of converters of solar radiation into electricity, namely, organic solar cells. It was shown that there were no differences in the composition of the initial dyes and the deposited ones, which is a proof of their thermal stability and a prerequisite for the reproducibility of the composition of the single and mixed layers under study. The results obtained are interpreted in view of the possible applicability of the layers studied for the fabrication of organic solar cells in which the processes of creation, the lifetime and the diffusion paths of the current carriers depend significantly on the film composition and the defects formed at the time of deposition of the active dye layers. © Published under licence by IOP Publishing Ltd.