Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 70Citation - Scopus: 76Humidity-Sensing Properties of a Zno Nanowire Film as Measured With a Qcm(Elsevier Ltd., 2011) Erol, Ayşe; Okur, Salih; Yağmurcukardeş, Nesli; Arıkan, M. ÇetinThe humidity-sensing properties of ZnO nanowires synthesized by carbothermal catalyst-free vapor solid (VS) technique were studied. The morphology and the crystal structure were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The humidity adsorption and desorption kinetics of the synthesized ZnO nanowires were investigated via quartz crystal microbalance (QCM) measurements. The observed positive frequency shift of ZnO nanowires when loaded on the QCM crystal under varying relative humidity conditions can be explained in terms of visco-elastic variations in their mechanical stiffness.Article Citation - WoS: 42Citation - Scopus: 42Investigation of Humidity Sensing Properties of Zns Nanowires Synthesized by Vapor Liquid Solid (vls) Technique(Elsevier Ltd., 2011) Üzar, Neslihan; Okur, Salih; Arıkan, M. ÇetinZinc sulfide (ZnS) nanostructures were synthesized by vapor-liquid-solid (VLS) method which is based on thermal evaporation. The morphology, chemical composition and crystal structure of ZnS nanostructures were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses. The results of these studies revealed that wurtzite ZnS nanowires with diameters in range of 50-400 nm are obtained. In order to investigate the humidity sensing capability, quartz crystal microbalance (QCM) and electrical resistance measurement techniques were carried out at different relative humidity (RH) conditions between 33% and 100% RH at room temperature. QCM results show that the oscillating frequency of ZnS nanowires loaded on QCM crystal decreases in range of 33-84% RH, but increases at 90% and 100% RH. The sensitivity of ZnS nanowires-based sensor (R air/RRH) increases over 1000 times from 33% to 100% RH. These experimental results show that ZnS nanowires have a great potential for humidity sensing applications at room temperature.Article Citation - WoS: 11Citation - Scopus: 13Magnetic Layer Formation on Plasma Nitrided Cocrmo Alloy(Elsevier Ltd., 2011) Öztürk, Orhan; Okur, Salih; Pichon, L.; Liedke, M. O.; Riviere, Jean PaulIn this study structural and magnetic character of the expanded austenite phase (γN) layer formed on a medical grade CoCrMo alloy by a low-pressure Radio-Frequency plasma nitriding process was investigated. The formation of the expanded austenite phase is facilitated at a substrate temperature near 400°C for 1, 2, 4, 6 and 20h under a gas mixture of 60% N2-40% H2. The magnetic state of the γN layers was determined by a surface sensitive technique, magneto-optic Kerr effect (MOKE), and with a scanning probe microscope in magnetic force mode (MFM). Strong evidence for the ferromagnetic nature of the γN-(Co,Cr,Mo) phase is provided by the observation of stripe domain structures and the hysteresis loops. The ferromagnetic state for the γN phase observed here is mainly linked to large lattice expansions (~10%) due to high N contents (~30at.%). As an interstitial impurity, nitrogen dilates the host lattice i.e. the Co-Co (or Fe-Fe) distance is increased, which strongly influences the magnetic interactions. An analogy between the magnetic properties of the expanded phases, γN-(Fe,Cr,Ni) and γN-(Co,Cr,Mo), formed in austenitic stainless steel alloys and the CoCrMo alloy of this study is made, and it is suggested that the ferromagnetic states for the γN-(Co,Cr,Mo) and γN-(Fe,Cr,Ni) phases may be correlated with the volume dependence of the magnetic properties of fcc-Co/Co4N and fcc-Fe/Fe4N, respectively.Article Citation - WoS: 5Citation - Scopus: 6New Approach for Consideration of Adsorption/Desorption Data(Elsevier Ltd., 2011) Baleanu, Mihaela Cristina; Nigmatullin, Raoul R.; Okur, Salih; Ocakoğlu, KasımIn this paper we proposed a new approach to modify the Langmuir model by considering nonlinear effects such as diffusion of water molecules in/out of an adsorbing film for humidity adsorption and desorption kinetics. The model was tested on the humidity adsorption and desorption data of a spin coated 50. nm thick Ruthenium polypridyl complex (Ru-PC K314) film, measured under relative humidity between 11% and 97% using by Quartz Crystal Microbalance (QCM) technique. © 2011 Elsevier B.V.Article Citation - WoS: 12Citation - Scopus: 16Humidity Adsorption Kinetics of a Trypsin Gel Film(Elsevier Ltd., 2012) Okur, Salih; Ceylan, Çağatay; Çulcular, EvrenThis study focuses on the humidity adsorption kinetics of an isopropanol-induced and pH-triggered bovine pancreatic trypsin gel (BPTG). The BPTG was adsorbed on a gold coated Quartz Crystal Microbalance (QCM) substrate with a thickness of 376nm. The morphology of the film was characterized using Atomic Force Microscopy (AFM). QCM was used to investigate the humidity sensing properties of the BPTG film. The response of the humidity sensor was explained using the Langmuir model. The average values of adsorption and desorption rates between 11% RH (relative humidity) and 97% RH were calculated as 2482.5M -1s -1 and 0.02s -1, respectively. The equilibrium constant and average Gibbs Free Energy of humidity adsorption and desorption cycles were obtained as 133,000 and -11.8kJ/mol, respectively. © 2011 Elsevier Inc..Article Citation - WoS: 17Citation - Scopus: 18Analysis of Interface States of the Pentacene Organic Thin-Film Phototransistor by Conductance Technique(Elsevier Ltd., 2009) Okur, Salih; Yakuphanoğlu, FahrettinA pentacene thin-film transistor with a channel width of 300 μm and a channel length of 30 μm has been successfully fabricated on n-Si substrate with thermally oxidized SiO2 as a gate insulator. The photovoltaic and interface state density properties of the transistor have been investigated. A pentacene film of 200 nm thickness was deposited on the SiO2 layer with a vacuum thermal evaporator. Atomic force microscopy images of the pentacene film on SiO2 insulating layer show a homogeneous film surface with the rms roughness of 11 nm. The transistor shows p-channel characteristics, as a result of positive carriers generated in the pentacene film for the negative bias voltages applied to the gate. The photosensitivity (Iph/Idark) is measured as 1.45 at an illumination intensity of 3500 lux at the off state. This suggests that the pentacene thin-film transistor shows a phototransistor characteristic. The field-effect mobility of the pentacene OTFT was found to be 0.021 cm2/(V s). The interface state density of the transistor was determined using conductance technique and was found to be about 1.191 × 1010 eV-1 cm-2.Article Citation - WoS: 34Citation - Scopus: 37Humidity Adsorption Kinetics of Water Soluble Calix[4]arene Derivatives Measured Using Qcm Technique(Elsevier Ltd., 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. © 2009 Elsevier B.V. All rights reserved.Article Citation - WoS: 138Citation - Scopus: 146Humidity Sensing Properties of Zno Nanoparticles Synthesized by Sol-Gel Process(Elsevier Ltd., 2010) Erol, Ayşe; Okur, Salih; Comba, B.; Mermer, Ömer; Arıkan, M. Ç.ZnO nanoparticles have been synthesized by the sol-gel method with approximately 10 nm diameter and the humidity adsorption and desorption kinetics of ZnO nanoparticles were investigated by quartz crystal microbalance (QCM) technique. The morphology and crystal structure of the ZnO nanoparticles have been characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The roughness of the surface has been investigated using atomic force microscope (AFM). The dynamic Langmuir adsorption model was used to determine the kinetic parameters such as adsorption and desorption rates and Gibbs free energy under relative humidity between 45% and 88%. The relative sensitivity of the ZnO nanoparticles-based humidity sensor was determined by electrical resistance measurements. Our reproducible experimental results show that ZnO nanoparticles have a great potential for humidity sensing applications at room temperature operations. © 2009 Elsevier B.V. All rights reserved.Article Citation - WoS: 36Citation - Scopus: 30Humidity Adsorption Kinetics of Calix[4]arene Derivatives Measured Using Qcm Technique(Elsevier Ltd., 2010) Okur, Salih; Kuş, Mahmut; Özel, Faruk; Aybek, Vildan; Yılmaz, 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. © 2009 Elsevier B.V. All rights reserved.Article Citation - WoS: 26Citation - Scopus: 24Cocrmo Alloy Treated by Floating Potential Plasma Assisted Nitriding and Plasma Based Ion Implantation: Influence of the Hydrogen Content and of the Ion Energy on the Nitrogen Incorporation(Elsevier Ltd., 2010) Pichon, L.; Okur, Salih; Öztürk, Orhan; Rivière, J. P.; Drouet, M.Nitriding was performed on a medical grade CoCrMo alloy at 400°C in N2 or N2-H2 atmosphere at a working pressure of 0.84Pa for 2h. Various surface treatment techniques were used to incorporate nitrogen into the CoCrMo alloy: without any plasma assistance, by floating potential radio-frequency plasma assisted nitriding (FPPAN), by plasma based ion implantation (PBII) with several high voltage accelerations (up to 20kV). Without plasma activation, no nitrogen is incorporated in the CoCrMo. On the contrary, all the plasma or PBII treated samples show the formation of a nitrogen-rich f.c.c. γN phase. The layer nitrided over few microns has a nitrogen composition ranging from 30at.% to about 20at.% near the nitrided layer-substrate interface, with an enhanced surface microhardness. Hydrogen is found to enhance the nitriding efficiency. Without hydrogen, a high voltage polarization provides a supplementary amount of implanted nitrogen available for further diffusion and the sputtering of the surface passive oxide. So, with limited high voltages, thicker layers with higher amounts of nitrogen can be achieved by PBII compared to plasma nitriding. However, with higher voltages, the sputtering becomes too important and the nitride layer is thinner. © 2010 Elsevier B.V.