Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Influence of High Content of Sodium Doping in Bi(pb)2212 Superconductors(Pleiades Publishing, 2023) Faiza, Bouaïcha; Mosbah, Mohamed-Fayçal; Özyüzer, LütfiAbstract: We study here, the effect of high content of sodium doping on structural and electrical properties of Bi(Pb)2212 superconductors. The X-ray analysis results showed that all the prepared samples mainly belong to the superconducting tetragonal phase Bi–(Pb)2212. SEM micrographs show that the grains are closely related and have a characteristic flat shape for the superconductor Bi (Pb) 2212. For the undoped sample, the grains are randomly distributed with an average size of 5 μm. For doped samples, the morphology changes with sodium concentration. Resistivity measurements show that all samples have a superconducting character. © 2023, Pleiades Publishing, Ltd.Article Citation - WoS: 6Citation - Scopus: 5Structural and Optical Characteristics of Antimony Selenosulfide Thin Films Prepared by Two-Step Method(Springer, 2022) Türkoğlu, Fulya; Ekren, Memduh Emirhan; Cantaş, Ayten; Yakıncı, Kübra; Gündoğan, Hazal; Aygün, Gülnur; Özyüzer, LütfiAntimony triselenide (Sb2Se3) is one of the most promising absorber material choices among the inorganic semiconductors that has attracted much attention today. However, highest recorded efficiencies for Sb2Se3 solar cells are still lower than ideal. Exploring antimony selenosulfide (Sb-2(SxSe1-x)(3)) to increase device performance is one option because some features of alloyed Sb-2(SxSe1-x)(3) depend on composition such as bandgap and band position. In this study, two-step process was used to grow Sb-2(SxSe1-x)(3) thin films. In the first stage, Sb2Se3 thin films were deposited on soda lime glass substrates using direct current magnetron sputtering technique. In the second stage, Sb2Se3 thin films were exposed to sulfurization process in a quartz ampoule to obtain Sb-2(SxSe1-x)(3) thin films. Characterization results showed that morphological, optical, and structural properties of Sb-2(SxSe1-x)(3) thin films grown by presented method were highly dependent on amount of sulfur in the films. By the adjustment of the S/S + Se atomic ratio, Sb-2(SxSe1-x)(3) absorber materials with suitable bandgap, favorable orientation and compact morphology can be obtained for photovoltaic applications.Article Citation - WoS: 2Citation - Scopus: 2Enhancing the Photo-Response Characteristics of Graphene/N-si Based Schottky Barrier Photodiodes by Increasing the Number of Graphene Layers(AVS, 2022) Fidan, Mehmet; Ünverdi, Özhan; Çelebi, CemThe impact of the number of graphene layers on the spectral responsivity and response speed of graphene/n-type Si (Gr/n-Si)-based Schottky barrier photodiodes is investigated. Gr/n-Si photodiode devices are fabricated by transferring chemical vapor deposition-grown graphene layers one by one on n-Si substrates, reaching up to three graphene layers. The devices show a clear rectifying Schottky character and have a maximum responsivity at a peak wavelength of 905 nm. Wavelength-resolved and time-dependent photocurrent measurements demonstrated that both spectral responsivity and response speed are enhanced as the number of graphene layers is increased from 1 to 3 on n-Si substrates. For example, the spectral responsivity and the response speed of the fabricated device were found to be improved by about 15% (e.g., from 0.65 to 0.75 AW-1) and 50% (e.g., 14 to 7 μs), respectively, when three graphene layers are used as the hole-collecting cathode electrode. The experimentally obtained results showed that the device parameters, such as spectral responsivity and response speed of Gr/n-Si Schottky barrier photodiodes, can be boosted simply by increasing the number of graphene layers on n-Si substrates.Article Citation - WoS: 3Citation - Scopus: 3Atomic-Scale Investigation of the Effect of Surface Carbon Coatings on the Oxidation and Mechanical Properties of Iron Nanowires(Royal Society of Chemistry, 2021) Aral, Gürcan; Islam, Md MahbubulThe understanding of the complex atomistic-scale mechanisms of the oxidation process of carbon (C) coated iron nanowires (Fe NW) and also the resulting modulation of mechanical properties is a highly challenging task. We perform reactive molecular dynamics (RMD) simulations based on the ReaxFF force field to investigate the mechanisms of the oxidation process of [001]-oriented pristine cylindrical Fe NWs with and without a C coating in an O2 environment in order to obtain detailed insights into the influences of the surface C coating on the oxidation process at room temperature. Here, we show that the C-coated shell layer on the free surface of pristine Fe NWs partially controls the spontaneous oxidation when exposed to O2 molecules by hindering the absorption-dissociation of O2 molecules and diffusion of O ions into the shell layer. In particular, the surface modification of the pristine Fe NW with the C-coated shell layer has pronounced effects on the improvement of oxidation resistance by lowering the surface reactivity, which limits the formation of an oxide shell layer on the free surface of the NW. The formation of strong Fe-C bonds in the C-coated shell layer largely restrains the oxidation process. Furthermore, to examine the influence of the C-coated shell layer on the resulting modulation of mechanical properties of the pristine Fe NW, we systematically investigate the mechanical deformation processes and related properties of Fe NW with and without a C coating including their oxidized counterparts subjected to both uniaxial tensile and compressive loads at room temperature. The yield stress and strain (the elastic limit) of Fe NWs including the elastic and plastic deformation phase of the stress-strain relationship are found to be sensitive to the loading modes, the existence of the C-coated shell layer and the resulting formation of an oxide shell layer on the surface of the C-coated Fe NW.Article Citation - WoS: 3Citation - Scopus: 3Compact Multilayer Thin-Film Color Filters and Direct Integration on White-Light Diodes for Color Conversion(Optical Society of America, 2021) Yiğen, Serap; Ekmekçioğlu, Merve; Özdemir, Mehtap; Aygün, Gülnur; Özyüzer, LütfiWe present highly efficient green, yellow, and red filters based on a metal-dielectric structure. The filters encompass only five layers of alternating zinc tin oxide and silver thin films that are grown on soda lime glass and white light-emitting diodes (LEDs) using direct current magnetron sputtering at room temperature. The designed filters provide efficient color filtering in the visible spectrum. High purity colored light is obtained by direct application of filters on LEDs as color converters. The presented method offers an easy way for realizing different colors by tuning the thicknesses of layers in the structure. (C) 2021 Optical Society of AmericaArticle Citation - WoS: 11Citation - Scopus: 13Effect of Cnt Incorporation on Pan/Ppy Nanofibers Synthesized by Electrospinning Method(TÜBİTAK, 2020) İnce Yardımcı, Atike; Tanoğlu, Metin; Yılmaz, Selahattin; Selamet, YusufIn this study, carbon nanotubes (CNTs) added polyacrylonitrile/polypyrrole (PAN/PPy) electrospun nanofibers were produced. Average diameters of the nanofibers were measured as 268 and 153 nm for 10 and 25 wt% of PPy contents, respectively. A relatively higher strain to failure values (23.3%) were observed for the low PPy content. When as-grown CNTs (1 and 4 wt%) were added into the PAN/PPy blends, disordered nanofibers were observed to form within the microstructure. To improve the interfacial properties of CNTs/PAN/PPy composites, CNTs were functionalized with H2SO4/HNO3/HCl solution. The functionalized CNTs were well dispersed within the nanofibers and aligned along the direction of nanofibers. Therefore, beads formation on nanofibers decreased. The impedance of the nanofibers was found to decrease with the PPy content and CNT addition. These nanofibers had a great potential to be used as an electrochemical actuator or a tissue engineering scaffold.Article Citation - WoS: 12Citation - Scopus: 13Electronic and Magnetic Properties of Graphene Quantum Dots With Two Charged Vacancies(Elsevier, 2020) Kul, Erdoğan Bulut; Polat, Mustafa; Güçlü, Alev DevrimElectronic and magnetic properties of a system of two charged vacancies in hexagonal shaped graphene quantum dots are investigated using a mean-field Hubbard model as a function of the Coulomb potential strength ? of the charge impurities and the distance R between them. For ?=0, the magnetic properties of the vacancies are dictated by Lieb's rules where the opposite (same) sublattice vacancies are coupled antiferromagnetically (ferromagnetically) and exhibit Fermi oscillations. Here, we demonstrate the emergence of a non-magnetic regime within the subcritical region: as the Coulomb potential strength is increased to ??0.1, before reaching the frustrated atomic collapse regime, the magnetization is strongly suppressed and the ground state total spin projection is given by Sz=0 both for opposite and same sublattice vacancy configurations. When long-range electron–electron interactions are included within extended mean-field Hubbard model, the critical value for the frustrated collapse increases from ?cf?0.28 to ?cf?0.36 for R<27Å. © 2020 Elsevier LtdArticle Citation - WoS: 6Citation - Scopus: 6Experimental and Density Functional Theory Study on Humidity Sensing Properties of Copper Phthalocyanine (cupc)(IOP Publishing, 2019) Farzaneh, Amir; Esrafili, Mehdi D.; Okur, SalihThe quartz crystal microbalance (QCM) technique was applied to investigate humidity sensing properties of a copper phthalocyanine (CuPc) thin film prepared by drop cast method. The humidity adsorption and desorption kinetics of (CuPc) thin film was evaluated. The QCM and electrical measurements results showed that humidity sensing properties of CuPc is very sensitive to humidity changes and reversible adsorption/desorption performance which is an indicative of a good humidity sensor even at room temperature. Reproducible experimental results indicated that CuPc thin films have an abundant potential for humidity sensing applications at ambient temperature. According to the first-principle density functional theory calculations, the promising humidity sensing properties of CuPc can be attributed to the considerable charge transfer from the water molecule into Cu atom.Article Citation - WoS: 5Citation - Scopus: 5Defect Induced Anderson Localization and Magnetization in Graphene Quantum Dots(Elsevier, 2018) Altıntaş, Abdulmenaf; Güçlü, Alev DevrimWe theoretically investigate the effects of atomic defect related short-range disorders and electron-electron interactions on Anderson type localization and the magnetic properties of hexagonal armchair graphene quantum dots using an extended mean-field Hubbard model and wave packet dynamics for the calculation of localization lengths. We observe that randomly distributed defects with concentrations between 1 and 5% of the total number of atoms leads to localization alongside magnetic puddle-like structures. Although the localization lengths are not affected by interactions, staggered magnetism and localization are found to be enhanced if the defects are distributed unevenly between the sublattices of the honeycomb lattice.Article Citation - WoS: 22Citation - Scopus: 24Are There Really Conformal Frames? Uniqueness of Affine Inflation(World Scientific Publishing Co. Pte Ltd, 2018) Azri, HemzaHere, we concisely review the nonminimal coupling dynamics of a single scalar field in the context of purely affine gravity and extend the study to multifield dynamics. The coupling is performed via an affine connection and its associated curvature without referring to any metric tensor. The latter arises a posteriori and it may gain an emergent character like the scale of gravity. What is remarkable in affine gravity is the transition from nonminimal to minimal couplings which is realized by only field redefinition of the scalar fields. Consequently, the inflationary models gain a unique description in this context where the observed parameters, like the scalar tilt and the tensor-to-scalar ratio, are invariant under field reparametrization. Overall, gravity in its affine approach is expected to reveal interesting and rich phenomenology in cosmology and astroparticle physics.