Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Book Part Citation - Scopus: 1Electrocaloric Ceramics(Elsevier, 2023) Alkoy, S.; Okatan, M.B.; Mısırlıoğlu, I.B.; Menşur-Alkoy, E.Electrocaloric effect (ECE) is a coupling between thermal and electrical phenomena, specifically it is the change in the entropy of a dielectric material as a result of an electrical stimulus. Electrocaloric materials are currently being investigated as a solid state refrigeration approach for on-chip cooling applications. Among the organic and inorganic electrocaloric material choices, electrocaloric ceramics are at the forefront with their higher electrocaloric coefficients. This article gives a background on the fundamentals of electrocalorics and then discusses the general trends in the literature on the electrocaloric ceramics research. © 2023 Elsevier Inc. All rights reservedArticle Citation - WoS: 24Citation - Scopus: 23Photovoltaic Performance of Magnetron Sputtered Antimony Selenide Thin Film Solar Cells Buffered by Cadmium Sulfide and Cadmium Sulfide /Zinc Sulfide(Elsevier B.V., 2023) Cantas, A.; Gundogan, S.H.; Turkoglu, F.; Koseoglu, H.; Aygun, G.; Ozyuzer, L.Antimony selenide (Sb2Se3)-based thin-film solar cells have recently attracted worldwide attention as an abundant, low-cost, and efficient photovoltaic technology. The highest efficiencies recorded for Sb2Se3 solar cells have been obtained using cadmium sulfide (CdS) as a buffer layer. The Cd-included hybrid buffer layers could be one option to increase device efficiency through more effective usage of light. Therefore, in this work, the effect of single CdS and hybrid CdS/zinc sulfide (ZnS) buffer layers on the photovoltaic performance of Sb2Se3 thin-film solar cells has been investigated in detail. Sb2Se3 thin films have been deposited on molybdenum (Mo)-coated soda-lime glass (SLG) substrates by radio frequency magnetron sputtering technique followed by a post-heat treatment process. The morphological, and structural properties of Sb2Se3 thin films have been investigated by X-Ray Diffraction and Scanning Electron Microscopy. To compare the device performances of single CdS and hybrid CdS/ZnS buffered Sb2Se3 thin-film solar cells, SLG/Mo/Sb2Se3/CdS/ZnS/indium tin oxide (ITO) and SLG/Mo/Sb2Se3/CdS/ITO structures have been fabricated. The findings of this study have revealed a reduction in solar cells’ performance from η=3.93% for CdS buffer to η=0.13% for CdS/ZnS hybrid buffer. The change in the solar cell performance using the CdS/ZnS hybrid buffer has been discussed in detail. © 2023 Elsevier B.V.Article Citation - WoS: 10Citation - Scopus: 12Enhanced Model Protein Adsorption of Nanoparticulate Hydroxyapatite Thin Films on Silk Sericin and Fibroin Surfaces(Springer, 2022) Özcan, Selçuk; Çiftçioğlu, MuhsinHydroxyapatite coated metallic implants favorably combine the required biocompatibility with the mechanical properties. As an alternative to the industrial coating method of plasma spraying with inherently potential deleterious effects, sol-gel methods have attracted much attention. In this study, the effects of intermediate silk fibroin and silk sericin layers on the protein adsorption capacity of hydroxyapatite films formed by a particulate sol-gel method were determined experimentally. The preparation of the layered silk protein/hydroxyapatite structures on glass substrates, and the effects of the underlying silk proteins on the topography of the hydroxyapatite coatings were described. The topography of the hydroxyapatite layer fabricated on the silk sericin was such that the hydroxyapatite particles were oriented forming an oriented crystalline surface. The model protein (bovine serum albumin) adsorption increased to 2.62 µg/cm2 on the latter surface as compared to 1.37 µg/cm2 of hydroxyapatite on glass without an intermediate silk sericin layer. [Figure not available: see fulltext.].Article Citation - WoS: 2Citation - Scopus: 2In-Situ Thin Film Copper-Copper Thermocompression Bonding for Quantum Cascade Lasers(Springer, 2021) Rouhi, Sina; Özdemir, Mehtap; Ekmekçioğlu, Merve; Yiğen, Serap; Demirhan, Yasemin; Szerling, Anna; Kosiel, Kamil; Kozubal, Maciej; Kruszka, Renata; Prokaryn, Piotr; Ertuğrul, Mehmet; Reno, John L.; Aygün, Gülnur; Özyüzer, LütfiThe choice of metals, bonding conditions and interface purity are critical parameters for the performance of metal-metal bonding quality for quantum cascade lasers (QCLs). Here, we present a novel approach for the thermocompression bonding of Cu-Cu thin films on GaAs-based waveguides without having any oxide phase, contamination or impurities at the interface. We designed a hybrid system in which magnetron sputtering of Ta, thermal evaporation of Cu and Cu-Cu thermocompression bonding processes can be performed sequentially under high vacuum conditions. GaAs/Ta/Cu and Cu/Ta/GaAs structures were thermocompressionally bonded in our in-situ homebuilt bonding system by optimizing the deposition parameters and bonding conditions. The grown thin film and the obtained interfaces were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX) techniques. The optimum Ta and Cu films' thicknesses were found to be about 20 nm and 500 nm, respectively. EDX analysis showed that the Ta thin film interlayer diffused into the Cu structure, providing better adhesivity and rigidity for the bonding. Additionally, no oxidation phases were detected at the interface. The best bonding quality was obtained when heated up to 430 degrees C with an applied pressure of 40 MPa during bonding process.Article Citation - WoS: 5Citation - Scopus: 5Comparison of Characteristic Properties of Al, Ga, and In-Doped Zno Thin Films Formed by Sol-Gel Method(Academic Press, 2021) Horzum, Şeyda; Bulduk, Emel; Şener, Deniz; Serin, TülayHerein, we examine the effect of doping with Indium (In), Gallium (Ga), and Aluminum (Al) (group III elements) on the structural, optical, and vibrational properties of ZnO thin films. The characteristic properties of the ZnO films prepared by the sol-gel dip-coating method are explored by utilizing X-ray diffraction, optical spectroscopy, and Raman scattering measurements. XRD analyzes exhibit that the crystallite size reduces upon doping by Ga and Al, while it increases with In, and all films have hexagonal wurtzite structure. Additionally, Raman measurements indicate that the dominant two peaks at around 104 and 445 cm(-1) are related to E(2)(low )and E-2(high) phonon modes of ZnO, respectively. The low-frequency mode (E-2(low)) is affected by dopant atoms, whereas the high-frequency mode (E-2(high)) of the wurtzite phase is not influenced by the dopant. Moreover, E-dop.atom phonon mode appears at low frequencies and the intensity ratio, I(E-dop.atom)/I(E(2)low), decreases as the ionic radius of dopant atoms increases. UV-Vis spectra reveal that the film transparency, optical band gap, Urbach energy, and refraction index can be effectively tuned by dopant atoms.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: 28Citation - Scopus: 29Oxidation of Nanocrystalline Aluminum by Variable Charge Molecular Dynamics(Elsevier Ltd., 2010) Perron, A.; Garruchet, S.; Politano, O.; Aral, Gürcan; Vignal, V.We investigate the oxidation of nanocrystalline aluminum surfaces using molecular dynamics (MD) simulations with the variable charge model that allows charge dynamically transfer among atoms. The interaction potential between atoms is described by the electrostatic plus (Es+) potential model, which is composed of an embedded atom method potential and an electrostatic term. The simulations were performed from 300 to 750 K on polycrystalline samples with a mean grain size of 5 nanometers. We mainly focused on the effect of the temperature parameter on the oxidation kinetic. The results show that, beyond a first linear regime, the kinetics follows a direct logarithmic law (governed by diffusion process) and tends to a limiting value corresponding to a thickness of similar to 3 nm. We also characterized at 600 K the effects of an external applied strain on the microstructure and the chemical composition of oxide films formed at the surface. In particular, we obtained a partially crystalline oxide films for all temperatures and we noticed a strong correlation between the degree of crystallinity of the oxide film and the oxidation temperature. (C) 2009 Elsevier Ltd. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 8Investigation of the Structural and Optical Properties of Copper-Titanium Oxide Thin Films Produced by Changing the Amount of Copper(Elsevier Ltd., 2019) Horzum, Şeyda; Gürakar, Sibel; Serin, TülayWe examine how the structural, morphological and optical properties of TiO2 thin films are changed with heavily copper (Cu) content. Variations in characteristic properties of the films with 0, 12.5, 25 and 50 wt% Cu contents, grown by sol-gel dip coating method, are observed by using X-ray diffraction (XRD), Raman scattering, atomic force microscopy, energy dispersive X-ray analysis and optical spectroscopy measurements. The XRD and Raman spectra indicate that pure TiO2 film forms in the anatase structure. At high Cu concentrations, XRD results also reveal the substitution of Ti with Cu and formation of extra compound Copper-Titanium oxide. Raman measurements also show that Cu is incorporated homogeneously into TiO2 matrix up to 12.5 wt% concentration and this uniformity is distorted at higher Cu contents. In addition, optical spectroscopy measurements show that the optical band gap energy decreases from 3.26 eV to 2.05 eV with increasing Cu concentration. Furthermore, it is observed that the refractive index values obtained by means of transmittance spectra at 550 nm wavelength; increases from 2.47 to 3.39 when the Cu concentration increases from 0 to 50 wt %.Article Citation - WoS: 28Citation - Scopus: 29Development of a High-Flux Thin-Film Composite Nanofiltration Membrane With Sub-Nanometer Selectivity Using a Ph and Temperature-Responsive Pentablock Co-Polymer(American Chemical Society, 2019) Bar, Canbike; Çağlar, Nagahan; Uz, Metin; Mallapragada, Surya K.; Alsoy Altınkaya, SacideProducing block co-polymer-based nanofiltration (NF) membranes with sharp molecular weight cutoffs via an efficient method exhibiting persistent size-based separation quality is challenging. In this study, this challenge was addressed by reporting a facile approach to fabricate pentablock co-polymer (PBC)-based thin-film composite (TFC) NF membranes. The PBC, consisting of temperature-responsive Pluronic F127 (PEO-b-PPO-b-PEO) middle blocks and pH-responsive poly(N,N-(diethylamino)ethyl methacrylate) end blocks, were synthesized by atom-transfer radical polymerization. This polymer was then attached electrostatically to the surface of polysulfone/sulfonated polyether-sulfone support membranes fabricated using a non-solvent-induced phase separation technique. The conformational changes of the PBC chains in response to pH and temperature determined the, pure water flux and neutral solute (PEG 1000) rejection performance of TFC membranes. Permeability of the membranes increased from 13.0 +/- 0.63 to 15.9 +/- 0.06 L/m(2).h bar and from 6.7 +/- 0.00 to 13.9 +/- 0.07 L/m(2).h.bar by changing the solution pH from 4 to 8.5 and temperature from 4 to 25 degrees C, respectively. The pH- and temperature-responsive conformational changes did not affect the PEG 1000 rejection and membrane pore radius, which remained constant at similar to 89% and similar to 0.9 nm, respectively. This important finding was attributed to the high grafting density of co-polymer chains, resulting in spatial limitations among the grafted chains. The pore size of similar to 0.9 nm achieved with the proposed membrane design is the smallest size reported so far for membranes fabricated from block copolymers. TFC membranes demonstrated high stability and maintained their flux and rejection values under both static (storage in an acidic solution for up to 1 month) and dynamic (filtering PEG 1000 solution over 1 week) conditions. Pentablock copolymers enable a NF membrane with a sharp molecular weight cutoff suitable for size-selective separations. The membrane fabrication technique proposed in this study is a scalable and promising alternative that does not involve complex synthetic routes.Article 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.