Browsing by Author "Çipiloglu, MA"

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    The radioluminescence and optical behaviour of nanocomposites with CdSeS quantum dot
    Keskin, IÇ; Türemis, M; Kati, MI; Kibar, R; Sirin, K; Çipiloglu, MA; Kus, M; Büyükcelebi, S; Çetin, A
    In this work, highly luminescent alloyed CdSeS QDs are successfully synthesized by two phase route method by using oleic acid (OA) as a surfactant. OA capped CdSeS QDs prepared in two different synthesis duration were compared in terms of luminescence and optical properties. The nanocomposites blended with CdSeS QDs which have highly luminescent efficiency in different ratios by Low Density Polyethylene (LDPE) and these nanocomposites were mainly investigated radioluminescence (RL) and optical properties (UV/VIS absorption). Structural, morphological, thermal properties of the nanocrystal and nanocomposites were examined using; XRD, FT-IR, TEM, SEM, TG-DTA techniques. OA capped CdSeS and also nanocomposites were showed two RL spectrum peaks in green and red region at around 528 nm and 710 nm respectively. Also, it is seen that the radioluminescence intensity changes linearly with the particle size of the QDs and about 12% size change of quantum dot led to a threefold increase in RL intensity. The luminescence glow curves are in compliance with absorption and fluorescence spectra. The absorption bands showed a significant blue shift for the nanocomposites as compare to powder CdSeS. The optical band gap of the OA capped CdSeS calculated as 1.77 eV. It was observed that the optical band gap of LDPE was decreased by the adding ratio of CdSeS from 3.71 eV to 2.25 eV. (C) 2017 Elsevier B.V. All rights reserved.
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    Effects of thermal oxidation temperature on vacuum evaporated tin dioxide film
    Çakmak, HM; Çetinkara, HA; Kahraman, S; Bayansal, F; Tepe, M; Güder, HS; Çipiloglu, MA
    In order to investigate the effect of thermal oxidation temperature on tin dioxide (SnO2), tin dioxide films were obtained on quartz substrates by vacuum evaporation of tin metal. The films were characterized by X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM), temperature dependent electrical resistivity measurement and optical absorption spectroscopy. The SEM images showed that the films are dense, continuous and are composed of nanoparticles and particle sizes are increased after thermal oxidation. From the X-ray measurement results, the films indicated two strong reflection peaks of tetragonal structure in the orientations of (101) and (200) at 20 = 33.8 degrees and 37.95 degrees, respectively. Intensity of the peaks increased with increasing thermal oxidation temperature. We found resistivity values of about 10(-4) Omega-cm. Optical absorption spectra of the films in the UV-Vis spectral range revealed that optical band gap (E-g) value of the films increases with increasing thermal oxidation temperature. (C) 2012 Elsevier Ltd. All rights reserved.
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    FIGURE OF MERIT OF ONE-DIMENSIONAL RESONANT TRANSMISSION SYSTEMS IN THE QUANTUM REGIME
    Çipiloglu, MA; Turgut, S
    The figure of merit, ZT, for a one-dimensional conductor displaying a Lorentzian resonant transmission probability is calculated. The optimum working conditions for largest ZT values are determined. It is found that, the resonance energy has to be adjusted to be several resonance widths away from the Fermi level. Similarly it is better for the temperature to be equal to several resonance widths. The approximate relationships, which can be a fairly good guide for designing devices, between different parameters tinder optimum working conditions are given.
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    Theoretical Investigation on Molecular Structure and Electronic Properties of BxLiyCluster for Lithium-Ion Batteries with Quantum ESPRESSO Program
    Çipiloglu, MA; Özkurt, A
    In this study, molecular structure and electronic properties of eleven BxLiy(x = 1-3, y = 1-3) clusters are examined using the Perdew, Burke and Ernezerhof (PBE) method in the Quantum ESPRESSO program. Three main groups, consisting of two atoms, three atoms and four atoms, are selected as the starting points. The stable configurations, their binding energies per atom (E-b), dissociation energy (Delta E), and the second difference in energy (Delta E-2), HOMO-LUMO (HOMO: Highest Occupied Molecular Orbital LUMO: Lowest Occupied Molecular Orbital) gaps, total energy, frequency, force on atom, point group, bond length, density of state (DOS) and band structures are investigated for BxLiy(x = 1-3, y = 1-3) clusters. The results of binding energies (E-b), dissociation energy (Delta E) and the second difference in energy (Delta E-2) show that BLi, BLi(2)first isomer, BLi(2)second isomer, B(2)Li(2)first isomer, B(2)Li(2)second isomer and BLi(3)are the most stable among all 11 molecules of BxLiy(x = 1-3, y = 1-3). The stability of BxLiy(x = 1-3, y = 1-3) clusters depend on both the formation of geometrical structures on the number of Li atoms. As the number of Li atoms in the group increases, the stability of B(x)Li(y)clusters also increases. Within each group formation of geometrical structures, the stability of B(x)Li(y)clusters changes. It is observed that they may change the capability of chemical reactions in B(x)Li(y)clusters.
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    HA Coating on Ti6Al7Nb Alloy Using an Electrophoretic Deposition Method and Surface Properties Examination of the Resulting Coatings
    Aydin, I; Bahçepinar, AI; Kirman, M; Çipiloglu, MA
    Ti and its alloys, which are commonly used in biomedical applications, are often preferred due to their proximity to the mechanical properties of bone. In order to increase the biocompatibility and bioactivities of these materials, biomaterials based on ceramic are used in coating operations. In this study, by using an electrophoretic deposition method, instead of on the Ti6Al4V alloy which is commonly used in the literature, a hydroxyapatite (HA) coating operation was applied on the surface of the Ti6Al7Nb alloy, and the surface properties of the coatings were examined. Ti6Al7Nb is a new-generation implant on which there have not been many studies. The voltage values which were used in the coating operation were 50, 100, 150 and 200 V, and the time parameter was stabilized at 1 min. In our method, when preparing the solution, HA, ethanol, and polyvinyl alcohol (PVA) were used. At the end of the study, by using an electron microscope (SEM) the microstructures of the coatings were examined; elemental analyses (EDS) of the coating surfaces were performed; and by using an X-radiation diffraction (XRD) method, the phases which the coatings contained and the concentration of these phases were determined, and the coating thickness, roughness, and hardness values were also determined. Also, by conducting a Scratch test, the strength of the surface combination was examined. At the end of the study, in each parameter, a successful HA coating was seen. By comparing parameters with each other, the ideal voltage value in this coating was determined. It was determined that the most suitable coating was obtained at 100 V voltage and 1 min deposition time.