Yazar "Okutan, Mustafa" seçeneğine göre listele

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    The electrical properties of nickel (II) phthalocyanine and phenyl-C-61-butyric-acid-methyl ester doped nematic liquid crystals under laser light
    (Wiley-Blackwell, 2015) Özdemir, Zeynep Güven; Canlı, Nimet Yılmaz; Yılmaz, Ömer; Kırsoy, Ahmet; Okutan, Mustafa; Köysal, Oğuz
    Because of increasing attention of technological device applications of liquid crystals (LCs), determination of their electrical properties becomes important. In this work, experimental optimization for concentration and laser power effects on nematic LC's voltage-controlled negative resistance behavior has been studied co-usage of nickel (II) phthalocyanine (NiPc) and phenyl-C-61-butyric-acid-methyl ester (PCBM) polymer in nematic liquid crystal (E63). NiPc concentration has been arranged to be between percentages changing from 1 to 5 wt%, whereas a 1 wt% of PCBM has been used in E63 LC. The LC cells have been exposed to 632-nm laser illumination with power of 0-100 mW, and the influence of laser illumination on current-voltage (I-V) characteristics has also been examined. According to I-V measurements of the LC composites under laser illumination, an increase in current has been observed because of dispersal agents of NiPc and PCBM. The possible reason behind this result can be the increase of the impurity ion in E63 under laser illumination. Ionic charge carriers can move freely in the volume of the LC structure and hence conductivity increases. The value of the current increases for NiPc doped E63 in the dark, and it increases further to a higher value under photo-irradiation because of the ionic charges caused by photo-excited electrons from NiPc to LC medium. The higher increase in conductivity has been observed to more efficient free-charge carrier collection provided by 5 wt% NiPc and 1 wt% PCBM doped in LC hybrid medium under laser irradiation. Copyright (C) 2015 John Wiley & Sons, Ltd.
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    The impact of NiPc additive and laser light dielectric properties of E63 nematic liquid crystal
    (Taylor & Francis Ltd, 2016) Kılıç, Mehmet; Özdemir, Zeynep Güven; Canlı, Nimet Yılmaz; Bulgurcuoğlu, Ayşe Evrim; Köysal, Oğuz; Yılmaz, Ömer; Okutan, Mustafa
    In this work, the electrical properties of the pure nematic liquid crystal (E63) and different concentrations Nickel Phthalocyanine (NiPc) doped (E63+1% NiPc, E63+3% NiPc and E63+5% NiPc) E63 have been investigated by means of dielectric spectroscopy measurements under laser light illumination. The variations of the real (epsilon') and imaginary (epsilon") parts of dielectric constant with frequency have been studied. According to e0 versus voltage graphics, threshold voltage, Vth has been calculated. It has been observed that while NiPc doping increases the Vth, the application of laser light has a remarkable decreasing effect on threshold voltage, Vth. The absorption coefficients, a, and relaxation times, tau, have also been calculated for determining the relaxation mechanism. It has been revealed that the relaxation type of these materials is nearly-Debye type regardless of the laser illumination. Moreover, the dielectric strength has been analysed both Debye and Cole-Cole models. Furthermore, conductivity mechanisms of these composites under dark and laser illumination have been investigated for four frequency regions. It has been shown that conductivity mechanism of the composites are not affected by application of laser light above omega = 6x10(4) rad/s.
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    Investigation of dielectric properties and diffraction efficiency enhancements caused by photothermal effect in DR9 dye-doped nematic liquid crystal
    (Elsevier Science Bv, 2011) Köysal, Oğuz; Okutan, Mustafa; Gökçen, Muharrem
    In this work, we studied dielectric properties and laser-induced refractive index changes originating from photothermal effects of liquid crystal material doped with Disperse Red 9 (DR9) dye. Dye concentration is arranged to be between percentages changing from 0.2 wt.% to 1 wt.% in E63 nematic liquid crystal. Nonlinear optical properties such as diffraction efficiency (eta) and refractive index modulation (Delta n) were investigated by diffraction grating measurements. It was found the diffraction efficiency of pure E63 nematic liquid crystal is 1%. As the doping amount of DR9 dye in nematic LC is increased, diffraction efficiency took higher values and the maximum diffraction efficiency of 10% was gained with E63 doped with 0.8 wt.%DR9 dye. Moreover. dielectric permittivity and dielectric anisotropy values of the samples were investigated in the frequency range of 100 Hz-10 MHz by using dielectric spectroscopy technique. It was observed that dielectric constant values of the liquid crystal material are strongly affected by doping with dye. (C) 2011 Elsevier B.V. All rights reserved.
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    Molecular orientation of nickel phthalocyanine doped nematic liquid crystal composite under magnetic field
    (Taylor & Francis Ltd, 2016) Özdemir, Zeynep Güven; Canlı, Nimet Yılmaz; Kılıç, Mehmet; Köysal, Oğuz; Yılmaz, Ömer; Okutan, Mustafa
    The electrical and dielectric properties of the nematic liquid crystal (E63) and Nickel Phthalocyanine (NiPc) doped E63 composite have been investigated by dielectric spectroscopy under 0-0.4T magnetic field. It has been observed that NiPc doping and external magnetic field, B decrease threshold voltage. Moreover, conductivity of the composite has an increasing tendency with magnetic field. Furthermore, a significant decrease in relaxation frequency with B has been interpreted as the simplification of molecular orientation. Hence, NiPc doping enhances the magnetic sensitivity of E63 and increases molecular orientation ability and conductivity.