Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Conference Object Citation - WoS: 7Citation - Scopus: 7Carbon Deposition on the Stainless Steels Substrates Using Pulsed Plasma(National Institute of Optoelectronics, 2008) Pat, Suat; Balbağ, Zafer; Cenik, I.; Ekem, Naci; Okur, Salih; Vladoiu, Rodica; Musa, GeavitWe have developed a generic method for carbon deposition method for any substrates from methane pulsed plasma. The generic method has been developed for carbon deposition on the stainless steels substrates using pulsed methane plasma. Pulsed plasma was produced at atmospheric pressure methane gas and room temperatures. Methane plasma was generated using with 25kV, 25kHz pulsed power supply. Discharge current approximately 300 mA. Stainless steels probes hold in the 32mm from the methane plasma. Probes dimensions were phi=30mm, h=8mm and 4 mm.Article Citation - WoS: 3Citation - Scopus: 4Electrical Characterization of Interdigitated Humidity Sensors Based on Cnt Modified Calixarene Molecules(Polish Academy of Sciences, 2013) Özbek, Cebrail; Çulcular, Evren; Okur, Salih; Yılmaz, M.; Kurt, M.In this study, we report on the optimization and characterization of chloroform soluble calix[4]arene derivative as a humidity sensor based on electrical properties. Due to the fact that calix[4]arene molecules are nonconductive, we modified the calix[4]arene molecules with carbon nanotubes with electrostatic bond in order to increase the conductance of calix[4]arene molecule (5,11,17,23-tetra-ter-butyl-25,27-dehydrazinamidcarbonilmetoxy-26,28- -dehydroxy-kalix[4]aren). Using photolithography technique, we fabricated interdigitated gold electrodes with 3 micrometers separation to investigate the electrical properties of carbon nanotubes modified calix[4]arene molecule where we used dropcast method to form a thin film of carbon nanotubes modified calix[4]arene molecule on the gold electrodes. Our reproducible experimental results indicated that the chloroform soluble carbon nanotubes modified calix[4]arene films have great potential for humidity sensing applications at room temperature operations.Conference Object Citation - WoS: 18Citation - Scopus: 21Gas Sensing Properties of Carbon Nanotubes Modified With Calixarene Molecules Measured by Qcm Techniques(Polish Academy of Sciences, 2012) Mermer, Ömer; Okur, Salih; Sümer, F.; Özbek, Cebrail; Sayın, S.; Yılmaz, MustafaThis study focuses on the characterization and optimization of calixarene modified carbon nanotube thin films for gas detection. Calixarene molecules were synthesized individually by considering their functional groups to attract the gas. Calixarene modified carbon nanotube based sensors were fabricated using drop-casting method on a quartz crystal microbalance gold electrode. Carbon monoxide, carbondioxide, oxygen and dry air were used as active gases for adsorption process, while high-purity nitrogen gas was used for desorption process. The selectivity and sensitivity of calixarene modified carbon nanotube are investigated in detail. Our experimental results show that functional calixarene modified carbon nanotube coated quartz crystal microbalance sensors are very sensitive and selective to gas of CO 2 at room temperature operation.Conference Object Citation - WoS: 6Citation - Scopus: 11Odor Adsorption Kinetics on Modified Textile Materials Using Quartz Microbalance Technique(Polish Academy of Sciences, 2012) Sarıışık, Merih; Okur, Salih; Asma, Ş.In this study, a functional product with aromatic oil and vitamins for use at aromatherapy and spa centers or personal care has been designed to improve life quality of users by using multifunctional products with good odor, moisturizing, relaxation, anti-aging effects. For this purpose, commercial berry berry oil was capsulated in β-cyclodextrin, and then applied to 100% cotton towel fabric. Quartz crystal microbalance sensors were used to investigate odor adsorption kinetics on modified textile materials for the first time. The frequency responses vs. time plot shows clear linear step responses to the change in the concentration of odor molecules coming from the container filled with berry berry applied textile. The results also reveal that TiO 2 coated quartz crystal microbalance sensors can be used as e-nose to sense odor from textile coated with berry berry oil containing β-cyclodextrin capsules.Article Citation - WoS: 3Citation - Scopus: 3Mgb2 Superconducting Thin Films Grown by Magnetron Sputtering(National Institute of Optoelectronics, 2007) Ulucan, Savaş; Özyüzer, Lütfi; Okur, SalihIn this study, we report the growth and properties of MgB2 thin films on polycrystalline Al2O3 substrates. A composite MgB2 target was produced by MgB2 and Mg powder mixing, using a hot pressing technique. MgB2 thin films were grown on Al 2O3 substrates by d.c. magnetron sputtering, without heating the substrate. To enhance the superconducting properties of the as-grown films and to increase the crystal quality, an ex-situ anneal process was applied. The crystal structure of the thin films was determined by X-ray diffraction. The resistivity versus temperature of the deposited MgB2 thin films was studied to examine the transition temperatures of the films under various magnetic fields. The effects of the annealing temperature and annealing time on the electrical properties of MgB2 thin films are revealed.Article Citation - WoS: 13Citation - Scopus: 12Mgb2 Superconducting Thin Films Sequentially Fabricated Using Dc Magnetron Sputtering and Thermionic Vacuum Arc Method(Elsevier Ltd., 2007) Okur, Salih; Kalkancı, M.; Pat, Suat; Ekem, Naci; Akan, Tamer; Balbağ, Zafer; Musa, G.; Tanoğlu, MetinIn this work, we discuss fabrication and characterization of MgB2 thin films obtained by sequential deposition and annealing of sandwich like Mg/B/Mg thin films on glass substrates. Mg and B films were prepared using DC magnetron sputtering and thermionic vacuum arc techniques, respectively. The MgB2 thin films showed superconducting critical transition at 33 K after annealing at 650 °C.Conference Object Citation - WoS: 1Citation - Scopus: 1Minority Carrier Properties of Microcrystalline Silicon Thin Films Grown by Hw-Cvd and Vhf-Pecvd Techniques(National Institute of Optoelectronics, 2005) Okur, Salih; Göktaş, Oktay; Güneş, Mehmet; Finger, Friedhelm; Carius, ReinhardOpto-electronic properties of μc-Si:H films prepared by hot-wire/catalytic chemical vapor deposition (HWCVD) and very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) techniques with various silane concentrations (SC) have been investigated using Raman spectroscopy, the steady-state photocarrier grating technique (SSPG), and the steady-state photoconductivity (SSPC). A correlation between the minority carrier transport properties and the microstructure has been found, using the dependence of the diffusion length (Ld) on the SC and Raman intensity ratio (I c RS) representing crystalline volume fractions. I C RS changes from 0.22 to 0.77. Ld increases with increasing Ic RS. It peaks around 0.5 with a maximum value of 270 nm, then decreases. Similar dependences of Ld on I C RS were obtained for films prepared by both HWCVD and VHF-PECVD. However, the grating quality factor measured on highly crystalline HWCVD films is substantially smaller than that found for VHF-PECVD films, indicating a relatively higher surface roughness present in the highly crystalline HWCVD films.Conference Object Citation - WoS: 16Citation - Scopus: 17Instability Phenomena in Microcrystalline Silicon Films(National Institute of Optoelectronics, 2005) Finger, Friedhelm; Carius, Reinhard; Dylla, Thorsten; Klein, Stefan; Okur, Salih; Güneş, MehmetMicrocrystalline silicon (μc-Si:H) for solar cell applications is investigated with respect to the material stability upon treatment of the material in various environments, followed by annealing. The material can be separated into two groups: (i) material with high crystalline volume fractions and pronounced porosity which is susceptible to in-diffusion of atmospheric gases, which, through adsorption or oxidation affect the electronic properties and (ii) compact material with high or low crystalline volume fractions which show considerably less or no influence of treatment in atmospheric gases. We report the investigation of such effects on the stability of μc-Si:H films prepared by plasma enhanced chemical vapour deposition and hot wire chemical vapour deposition.Conference Object Citation - WoS: 7Citation - Scopus: 10Sub-Bandgap Absorption Spectroscopy and Minority Carrier Transport Properties of Hydrogenated Microcrystalline Silicon Thin Films(National Institute of Optoelectronics, 2005) Güneş, Mehmet; Göktaş, Oktay; Okur, Salih; Işık, Nebile; Carius, Reinhard; Klomfaß, Josef; Finger, FriedhelmHydrogenated microcrystalline silicon thin films have been prepared using HW-CVD and VHF-PECVD techniques with different silane concentrations. The steady-state photoconductivity, dual beam photoconductivity, photothermal deflection spectroscopy and steady-state photocarrier grating (SSPG) methods have been used to investigate the optical and electronic properties of the films. Two different sub-bandgap absorption methods have been applied and analyzed to obtain a better insight into the electronic states involved. For some films, differences existed in the optical absorption spectra when the measurements were carried out through the film side and through the substrate side. In addition, for some films, fringe patterns remained on the spectrum after the calculation of the fringe free absorption spectrum, which indicates that structural inhomogeneities were present throughout the film. Finally, minority carrier diffusion lengths deduced from the SSPG measurements were investigated as a function of the crystalline volume fraction (I c RS) obtained from Raman spectroscopy. The longest diffusion lengths and lowest sub-bandgap absorption coefficients were obtained for films deposited in the region of the transition to the amorphous growth.Conference Object Citation - WoS: 3Citation - Scopus: 2Fabrication of Superconducting Mgb2 From Boron Oxide (b 2o3), and Its Microstructural and Electrical Characterization(National Institute of Optoelectronics, 2005) Yavaş, Mert; Okur, Salih; Eğilmez, Mehmet; Kalkancı, Mihriban; Özyüzer, LütfiThe discovery of superconducting MgB2 (39 K) draws attention to it as a new material for applications based on superconductivity. Many researchers successfully synthesized MgB2 using commercial boron and magnesium. In this study, elementary boron was obtained via an acid leaching process, after reacting B2O3, and Mg in an argon atmosphere at 800°C. Energy Dispersive X-ray Spectroscopy (EDX) results revealed that the powder obtained from the reaction was boron in 92% purity with magnesium as the major impurity. Superconducting MgB2 was produced from this boron and magnesium, in an argon atmosphere at 900°C, by a conventional solid-state reaction. Superconducting MgB2 powders were compressed in a dye to pellets by a hot pressing technique at 500°C and 1 GPa. The microstructural properties of the MgB2 were determined by X-ray Diffraction Spectroscopy, EDX, and Scanning Electron Microscopy techniques. The electrical properties of the fabricated MgB 2 were examined by resistivity measurements in a closed-cycle cryopump system, between 20 and 300 K. The critical temperature (Tc) of the MgB2 pellets was around 32 K.