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Öğe Effect of doping on thin film solar cell efficiency based on ZnMn2O4 nanocrystals(ELSEVIER, 2019) Sarılmaz, Adem; Özel, Faruk; Aljabour, Abdalaziz; Khaskheli, Abdul Rauf; Kuş, MahmutThe present study reports, for the first time, a facile synthesis for ternary ZnMn2O4 nanocrystals synthesized by a simple and low cost two-phase method. Those nanocrystals were used on thin film solar cell as active absorber layer. The resulting nanocrystals were characterized by XRD, TEM, AFM-MFM, FTIR and JV characterization techniques to investigate the crystalline behavior, chemical composition, morphology and optical properties. Two phase method allows the successful synthesis of oleic acid (OA) capped ZnMn2O4 nanocrystals with 5-10 nm particle size. After doping of the ZnMn2O4 nanocrystals at different ratios with P3HT:PCBM, an enhancement was observed in the solar cell performances based on thin films. The power conversion efficiency of P3HT:PCBM-ZnMn2O4 thin film solar cell was investigated by J-V characteristic curve and as a result of this study, the highest efficiency was achieved as 3.27% with a doping ratio of 1%. Thus we believe that this work will open a new perspective to the synthesis of ZnMn2O4 materials for applications in the field of energy conversion systems. (C) 2019 Elsevier Ltd. All rights reserved.Öğe Enhanced Radiative Decay Rate of Confined Green Fluorescent Protein in Polyvinylpyrrolidone-Based Nanofiber(AMER CHEMICAL SOC, 2016) Açıkgöz, Sabriye; Ulusu, Yakup; Yüngeviş, Hasan; Özel, Faruk; Özen, Abdurrahman; Gökçe, İsa; Kara, KorayGreen fluorescent protein (GFP) molecules are encapsulated by polyvinylpyrrolidone material in the forth of nanofibers to study their diameter dependence of the fluorescence decay rate. Fluorescence dynamics of the confined GFP is governed by the Purcell effect. It is demonstrated that the electrospun nanofibers are quite controllable geometries and are suitable local photonic environments for exploring such effects. The chromophore of GFP, responsible for the intense green fluorescence, is attached to the alpha helix and perfectly surrounded by an 11-stranded beta-barrel cylinder. It is clearly observed that the molecular structures of the confined GFP protein molecules are well protected and are able to maintain their fluorescence properties.Öğe Humidity Adsorption Kinetics of Calix[4]arene Derivatives Measured Using QCM Technique(Elsevier, 2010) Okur, Salih; Kuş, Mahmut; Özel, Faruk; Aybek, Vildan; Yilmaz, MustafaThis study focuses on the characterization of sulphonated calix[4]arene derivative films coated on a quartz substrate with a thickness of 40 nm by spin coating method for humidity detection. The humidity adsorption kinetics of the sulphonated calix[4]arene films was investigated by quartz crystal microbalance (QCM) technique. The Langmuir model was used to determine the adsorption rates and Gibbs free energy for various relative humidities between 11% and 97%. Our reproducible experimental results show that suphonated calix[4]arene films have a great potential for humidity sensing applications at room temperature operations.Öğe Humidity Adsorption Kinetics of Water Soluble Calix[4]arene Derivatives Measured Using QCM Technique(Elsevier Science Sa, 2010) Okur, Salih; Kuş, Mahmut; Özel, Faruk; Yılmaz, MustafaWe report on the optimization and characterization of water soluble calix[4]arene derivative as a humidity sensor based on quartz crystal microbalance technique. The moisture adsorption and desorption kinetics of calix[4]arene were investigated. The Langmuir model was used to determine the kinetic parameters such as adsorption. desorption rates and Gibbs free energy between relative humidity between 29% and 78%. Reproducible experimental results were obtained showing that water soluble calix[4]arene films have a great potential for humidity sensing applications at room temperature operations.Öğe Improvement in electrical performance of half-metallic Fe3O4/GaAs structures using pyrolyzed polymer film as buffer layer(TAYLOR & FRANCIS LTD, 2014) Akın, Seçkin; Özel, Faruk; Kuş, Mahmut; Sönmezoğlu, SavaşIn this work, the Fe3O4 magnetic nanoparticles (MNPs) were synthesized by a colloidal method. TEM images reveal that Fe3O4 MNPs are spherical in shape with a narrow size distribution in the range of 6-7 nm. These MNPs were used in the fabrication of two types of n-GaAs-based structures: (i) Fe3O4/n-GaAs (reference); and (ii) Fe3O4/PPF/n-GaAs. We present that carbon-based pyrolyzed polymer films (PPFs), as a buffer layer, can control the electrical characteristics of a conventional Fe3O4/n-GaAs device. The behaviour of the apparent barrier height and ideality factor with the interfacial layer due to the presence of the interface state density is discussed. PPF raises the barrier height in a Fe3O4/PPF/n-GaAs half-metallic/insulator/semiconductor (h-MIS) device as high as 0.62 +/- 0.002 eV. Furthermore, Fe3O4/PPF interfaces exhibit unique electronic properties including high-quality interface, low series resistance (from 17.73 k Omega to 85.66 Omega) and extremely low interface state density (1.76 x 10(12) eV(-1) cm(-2)). Compared to the electrical performance for the Fe3O4/n-GaAs junction, that for the Fe3O4/PPF/n-GaAs junction was enhanced.Öğe Improvement of Catalytic Activity by Nanofibrous CuInS2 for Electrochemical CO2 Reduction(AMER CHEMICAL SOC, 2016) Aljabour, Abdalaziz; Apaydın, Doğukan Hazar; Coşkun, Halime; Özel, Faruk; Ersöz, Mustafa; Stadler, Philipp; Sarıçiftci, Niyazi SerdarThe current study reports the application of chalcopyrite semiconductor CuInS2 (CIS) nanofibers for the reduction of CO2 to CO with a remarkable Faradaic efficiency of 77 +/- 4%. Initially the synthesis of CuInS2 nanofibers was carried out by adaptable electrospinning technique. To reduce the imperfection in the crystalline fiber, polyacrylonitrile (PAN) was selected as template polymer. Afterward, the desired chemical structure of nanofibers was achieved through sulfurization process. Making continuous CuInS2 nanofibers on the cathode surface by the electrospinning method brings the advantages of being economical, environmentally safe, and versatile. The obtained nanofibers of well investigated size and diameter according to the SEM (scanning electron microscope) were used in electrochemical studies. An improvement of Faradaic efficiency was achieved with the catalytic active CuInS2 in nanofibrous structure as compared to the solution processed CuInS2. This underlines the important effect of the electrode fabrication on the catalytic performance. Being less contaminated as compared to solution processing, and having a well-defined composition and increased catalytically active area, the CuInS2 nanofiber electrodes prepared by the electrospinning technique show a 4 times higher Faradaic efficiency. Furthermore, in this study, attention was paid to the stability of the CuInS2 nanofiber electrodes. The electrochemical reduction of CO2 to CO by using CIS nanofibers coated onto FTO electrodes was carried out for 10 h in total. The observed current density of 0.22 mA cm(-2) and the stability of CIS nanofiber electrodes are found to be competitive with other heterogeneous electrocatalysts. Hence, we believe that the fabrication and application of nanofibrous materials through the electrospinning technique might be of interest for electrocatalytic studies in CO2 reduction.Öğe Kolloidal manyetik nanoparçacıkların sentezi ve elektronik optoelektronik devre uygulamaları(Selçuk Üniversitesi Fen Bilimleri Enstitüsü, 2014) Özel, Faruk; Kuş, MahmutBu tez çalışmasında; Manyetik özellikte, Fe3O4, MFe2O4 (M=Mn,Ni,Zn), ZnMn2O4 ve nikel nanokristaller, Fe3O4 süperpartiküller ve elektrospin fiberler sentezlenmiş ve yapısal karakterizasyonları yapılmıştır. Kolloidal yöntemin tercih edildiği sentezlerde nanokristallerin boyutları 5-10 nm civarında iken süperpartiküllerin 200 nm civarında oldukları gözlemlenmiştir. Bunun yanında elektrospin yöntemi ile manyetik özellikli Fe3O4 fiberlerin eldeside başarıyla gerçekleştirilmiştir. Sentezlenen manyetik malzemelerin aygıt uygulamaları yapılmış ve sonuçlar değerlendirilmiştir. Fe3O4 nanokristallerinin aktif Polifloren içerisine katkılanmasıyla elde edilen OLED yapılarında katkılama oranı %1 olduğunda ışık parlaklığının %50–60 oranında arttığı gözlemlenmiştir. ZnMn2O4 nanokristallerinin katkılandığı organik güneş pili uygulamalarında da verimlilikte artışlar gözlemlenmiştir. Yapılan sentez çalışmaları ve uygulamalar neticesinde, elde edilen manyetik malzemelerin birçok farklı uygulama alanında kullanıma elverişli fiziksel ve kimyasal özelliklere sahip oldukları gözlemlenmiştir.Öğe NiO and Co3O4 nanofiber catalysts for the hydrogen evolution reaction at liquid/liquid interfaces(PERGAMON-ELSEVIER SCIENCE LTD, 2018) Yanalak, Gizem; Aljabour, Abdalaziz; Aslan, Emre; Özel, Faruk; Patır, İmren Hatay; Kus, Mahmut; Ersöz, MustafaThe development of the non-precious, earth abundant and inexpensive catalysts with high catalytic efficiency for the electrocatalytic hydrogen evolution reaction acts an essential role in sustainable energy conversion and storage. Herein, we report that hydrogen evolution in two-phase systems by an organic soluble electron donor decamethylferrocene (DMFc) has been efficiently catalyzed by Co3O4 and NiO nanofiber catalysts, which are fabricated by the low-cost and simple electrospinning method. The catalytic activities of these metal oxide nanofibers have been examined by two-phase reactions and four-electrode cyclic voltammetry methods at water/1,2 dichloroethane interface. The hydrogen evolution reaction rate of nanofiber catalysts is also compared to the bulk forms of these metal oxide catalysts. The reaction rate is increased 74, 152, 284 and 384 times by using bulk and nanofiber forms of Co3O4 and NiO, respectively, when compared to an uncatalyzed reaction. The higher catalytic activity of the metal oxide nanofibers can be ascribed to the enhanced surface to volume ratio revealed from the fibrous structures. (c) 2018 Elsevier Ltd. All rights reserved.Öğe Organik molekül temelli gaz sensörü çalışmaları(Selçuk Üniversitesi Fen Bilimleri Enstitüsü, 2010) Özel, Faruk; Kuş, MahmutBu çalışmada çeşitli kaliks[4]aren moleküllerinin bazı organik çözücü ve su moleküllerine karşı davranışları Kuartz Kristal Mikrobalans (QCM) tekniği ile incelenmiştir. QCM ile yapılan ölçümlerde kaliksaren çözeltisi damlatma (drop casting) ve döndürme (spin coater) kaplama teknikleri ile QCM kristaline kaplanmış ve özel bir düzenek yardımı ile buhar fazındaki su, toluen, DMF, metanol, aseton moleküllerine karşı tepkileri ve moleküler arası etkileşimler incelenmiştir. Denemelerde en iyi sonuç sülfonat ve karboksilat grubu içeren kaliksarenlerin su molekülleri ile etkileştirilmesinde elde edilmiştir. Ayrıca çalışma sonucunda elde edilen bilgi birikimi ile birçok sektöre fayda sağlanabilecektir.
