Yazar "Ozkendir, O. M." seçeneğine göre listele

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    A study of the electronic and physical properties of SnO2 thin films as a function of substrate temperature
    (Elsevier Sci Ltd, 2019) Erken, O.; Ozkendir, O. M.; Gunes, M.; Harputlu, E.; Ulutas, C.; Gumus, C.
    In this work, tin dioxide (SnO2) thin films were prepared at various substrate temperatures (380-440 degrees C, in steps of 20 degrees C) on glass substrates by the Spray Pyrolysis Method. X-ray Diffraction (XRD) measurements revealed that the SnO2 thin films were formed in a tetragonal crystallized structure. The electronic structure of the tin dioxide thin films that were prepared at several substrate temperatures were investigated with the collected X-ray Absorption Spectroscopy (XAS) data. The crystal structure analysis was also supported by the Extended X-ray Absorption Fine Structure (EXAFS) data analysis extracted from the X-ray Absorption Fine Structure (XAFS) data. Unstable crystal behaviors were detected in the samples due to metastable SnO structure formations as a result of phase transitions from the SnO to SnO2 structure during the annealing processes. Clear information on the atomic displacements in the samples as a picture of the crystal mechanism was obtained from the analysis of EXAFS data. The SnO2 thin films were found to exhibit high transmittance (average 90%) in the 400-1100 nm interval. The thickness of the SnO2 thin film (t) and refractive index (n) were calculated from transmittance spectra in the visible region using envelope method. The direct energy band gaps of the films obtained were 4.01-4.09 eV. Atomic force microscope (AFM) measurements were performed in order to investigate the surface roughness of the SnO2 thin films.
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    Influence of Sn substitution on the electronic structure of ThGeO4 semiconductors
    (Natl Inst Optoelectronics, 2021) Ozkendir, O. M.
    ThGeO4 (TGO) material is an actinide semiconductor with a wide bandgap. The influence of Sn substitution in the Ge coordinations has probed by the x-ray absorption fine structure (XAFS) spectroscopy calculations. Calculations were performed for Th L-3-edge and O K-edge to study the influence of both Ge and the substituted Sn atoms on the electronic structure of the thorium atoms. ThO2 material's calculation has been used as reference material during the analysis and the analysis have shown that unoccupied 6d levels of the Th atoms' were hybridized with 2p levels of the oxygen to build up molecular bands.
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    Influence of temperature dependence and Li substitution on the electronic structure of delafossite CuFeO2 and CuFeS2 semiconductors
    (Elsevier Sci Ltd, 2021) Ozkendir, O. M.
    The electronic structure properties of the delafossite CuFeO2 and Chalcopyrite CuFeS2 semiconductors were stud-ied by XAFS technique theoretically. Calculations were performed with the XAFS code FEFF 8.20 under increasing temperature conditions for 300 K, 350 K, 450 K, 500 K, and for 20% Li substitution at room temperature. High stability in the electronic structure of both materials addressed was observed as a result of the hybridized states built with the contribution of the overlapped outer shell electrons and levels of the neighboring atoms, i.e., Cu, Fe, O or S. The hybridized levels were determined as supporting the stability of the molecular bands via rich quantum symmetries. For the second step of the studies, 20% Li substitution in copper coordination was pro-cessed to probe the response of the materials to substitution mechanisms. In the CuFeO2 semiconductors, 0.5 eV shift was observed with the Li substitution at the Fe K-edge absorption spectra which caused a loose in the Li-O bonds as a result of the weaker electronegativity which increased the strength of the Fe-O bonds.
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    Investigation on the electronic and physical properties of gamma-MnS films as a function of thickness
    (Elsevier Sci Ltd, 2022) Ulutas, C.; Erken, O.; Gunes, M.; Ozkendir, O. M.; Gumus, C.
    In this study, gamma-manganese sulphide (gamma-MnS) films were prepared at various thickness and deposition time at a temperature of 50 degrees C by Chemical Bath Deposition Method (CBD). The characterization of the gamma-MnS films were determined by using the following methods; X-ray Absorption Fine Structure Spectroscopy (XAFS), Xray diffraction (XRD), optical absorption, Field Emission-Scanning Electron Microscope (FE-SEM), Energy Dispersive X-ray analysis (EDX). The electronic interplay via the coupling between Mn 3d levels and S 2p levels was determined to build up strong molecular bonds containing broad band with hybrid pd levels at low energy levels. The results of the electronic structure analysis were also tested with the absorption spectroscopy calculations and high agreement is reported. XRD analysis revealed that the film deposited for 5 h had amorphous structure and turned to be crystal structure in hexagonal phase with deposition time 10, 15, 20 h due to increasing film thickness value. The optical band gap values were reduced from 3.86 eV to 3.10 eV with increasing film thickness. The average refractive index value of films at visible region were calculated between 1.55 and 2.81 as a function of increment in film thickness. The mobility and resistivity of the films were measured as 8.65-55.76 cm2/Vs and 3.10 x 105-2.39 x 106 omega cm, respectively, by Hall measurement.
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    Optical and structural characterization of (Mn, Fe) co-doped lead chalcogenides for optoelectronics applications
    (Natl Inst Optoelectronics, 2021) Merabet, B.; Ozkendir, O. M.; Hassanien, A. S.; Maleque, M. A.
    Lead chalcogenides (LCs) exhibit non-stability and lower device efficiency due to smaller bandgap (E-g) leading to poor optical properties for photovoltaic (PV) applications. In this work, optical properties of transition metals (TMs) such as (Mn and Fe) co-doped with LCs especially PbS in the framework of DFT+U (8 eV) and L/APW+/o method are theoretically investigated to predict new optical material for photovoltaic and other optoelectronics applications. The XAFS spectroscopy technique was used to analyze electronic structures and optical properties of (Mn, Fe) co-doped LCs. Midgap states of co-doped PbS reveal to improve the absorption of infrared light mainly due to slight doping with TMs. Compared to pure PbS, Mn doping in PbS induces E-g widening, blue-shift, and improve the light absorption edge. Due to co-doping, the magnetic order is translated that can lead to forming a charge compensated system which is beneficial to minimize vacancies related to defects formation.
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    Spin-orbit coupling effect on the electronic structure of Sr2FeHfO6 alloy for spintronics application
    (Elsevier, 2021) Merabet, B.; Ozkendir, O. M.; Hassanien, A. S.; Maleque, M. A.
    Strong spin-orbit coupling (SOC) in Sr2FeHfO6 (SFHO) alloy has been predicted by means of full-potential linear augmented plane wave method in order to study the effect on electronic structure. The tetragonal (I4/mmm) SFHO with SOC has an up-spin energy of similar to 1.2 eV and a total magnetic moment of similar to 2.03 mu B mainly coming from the Fe (1.63 mu B), and the SOC effect was prominent in SFHO due to the magnetic moment of 3d-Fe orbitals. The XAFS spectroscopy technique was used in order to analyze the electronic structure and optical properties of SFHO. The absorption spectra with Fe as a source atom shows a peak appearing around 7118 eV. SFHO with SOC falls within the half metallic state in the up-spin direction resulting significant increase of the total magnetic moment. This half-metallicity strong SOC in SFHO demonstrate much spin polarized electrons around the Fermi level, hence, this material is very potential in future memory devices and spintronic applications.