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    A Study of Crystallization in Plasma Modified Polypropylene
    (Elsevier, 2019) Mansuroglu, Dogan; Mecit, Giray; Uzun-Kaymak, Ilker Umit
    A capacitively coupled radio-frequency plasma discharge is used to improve the surface properties of Polypropylene. The changes in the surfaces are investigated for various plasma discharge parameters. After the plasma modification, the polypropylene material transforms into a para-crystalline form and shows the properties of the monoclinic crystals dominantly, observed using the X-ray diffraction measurements. The results indicate significant improvements in the crystallinity after the plasma exposure. These improvements are verified by the formations measured using a scanning electron microscope. Additionally, formations of new functional groups are observed using a Fourier transform infrared-attenuated total reflection spectrometer. (C) 2019 Elsevier Ltd. All rights reserved.
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    Argon and nitrogen plasma modified polypropylene: Surface characterization along with the optical emission results
    (Elsevier Science Sa, 2019) Mansuroglu, Dogan; Uzun-Kaymak, Ilker Umit
    This study focuses on the surface modifications of polypropylene using a capacitively coupled radio frequency gas discharge system. Improvements on the polymer surface properties are investigated for the case of argon and nitrogen plasmas at different radio frequency input power values. Higher number of reactions and their repetitions are expected by the charged particles at higher input power setting. On the other hand, the optical emission intensity does not change linearly with increasing RF input power. In addition to the optical emission spectroscopy, all chemical changes and formation of new functional groups are investigated using a Fourier transform infrared-attenuated total reflection spectrometer. Different reactions are observed for argon and nitrogen plasmas due to their ionization energies and their response to the polymer material. Changes in the surface morphologies are measured using a scanning electron microscope. Formed structures with different sizes and shapes are observed on the surfaces. Furthermore, it is observed that the originally hydrophobic type polypropylene surface is changed to a hydrophilic type after the plasma modification. Wettability of the surface is characterized by measuring the water contact angle. These changes due to the plasma exposure are discussed in detail for various discharge parameters.
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    Enhancement of electrical conductivity of plasma polymerized fluorene-type thin film under iodine and chlorine dopants
    (Elsevier Science Sa, 2017) Mansuroglu, Dogan; Uzun-Kaymak, Ilker Umit
    Electrical and optical properties of plasma-polymerized fluorene-type (C13H10) iodine-and chlorine-doped thin films are investigated. Fluorene-type thin films are produced using a mixture of biphenyl (C12H10) and methane (CH4) inside a single capacitively coupled radio frequency plasma system. The dopants are mixed with the plasmadirectly as vapor during the deposition. The chemical structures of the generated functional compounds, evaluated by a Fourier transform infrared spectroscopy, exhibit a changeable extension conjugation providing high crosslinking and branching. The structural orders of the doped films are analyzed using X-ray diffraction measurements. The film thickness is measured by ellipsometry. Measured difference in thickness due to doping varies from 16 nm to 50 nm. The structural characterization shows that the doped films are stable and of high quality. The current-voltage characteristics of devices are obtained using two-point probe measurements. As a result of doping, electrical conductivity as high as two orders of magnitude compared to that of the undoped films is measured. In addition, ultraviolet-visible spectroscopy is used to characterize the optical properties. Optical energy band gaps of the doped films as low as 2.4 eV are obtained. In conclusion, plasma processing is proven to improve the optical and electrical properties of the doped films. (C) 2017 Elsevier B.V. All rights reserved.
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    Experimental analysis on the nonlinear behavior of DC barrier discharge plasmas
    (Institute of Physics Publishing, 2017) Mansuroglu, Dogan; Uzun-Kaymak, Ilker Umit
    Nonlinear behavior of glow discharge plasmas is experimentally investigated. The glow is generated between a barrier semiconductor electrode, Chromium doped namely Gallium Arsenide (GaAs:Cr), as a cathode and an Indium-Tin Oxide (ITO) coated glass electrode as an anode, in reverse bias. The planar nature of electrodes provides symmetry in spatial geometry. The discharge behaves oscillatory in the time domain, with single and sometimes multi-periodicities in plasma current and voltage characteristics. In this paper, harmonic frequency generation and transition to chaotic behavior is investigated. The observed current-voltage characteristics of the discharge are discussed in detail. © 2016 Hefei Institutes of Physical Science, Chinese Academy of Sciences and IOP Publishing.
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    Investigation into Ex-Situ and In-Situ Iodine Doped Plasma Polymerized Fluorene-type Thin Films
    (Elsevier, 2019) Mansuroglu, Dogan; Uzun-Kaymak, Ilker Umit
    Effect of doping is investigated by applying iodine dopant to plasma polymerized fluorene (C13H10)-type thin films utilizing two separate techniques: ex-situ and in-situ doping. In this study, the thin films are produced using a mixture of biphenyl and methane in a capacitively coupled glow plasma system. Produced thin films are characterized using a fourier transform infrared spectrometer, an ultraviolet-visible spectrometer, a scanning electron microscope, and a two-point probe technique of the current - voltage characteristics. The results show that the in-situ doping technique is more effective than the ex-situ doping technique based on the improvements observed. (C) 2019 Elsevier Ltd. All rights reserved.