Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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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: 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.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.Conference Object Citation - WoS: 7Citation - Scopus: 8Properties of Reactive O2 Ion Beam Sputtered Tio2 on Si Wafers(National Institute of Optoelectronics, 2005) Ulucan, Savaş; Özyüzer, Gülnur Aygün; Özyüzer, Lütfi; Eğilmez, Mehmet; Turan, RaşitTiO2 thin films were deposited on silicon (100) p-type wafers, using the reactive ion beam sputtering method in high vacuum as an alternative to conventional Argon ion beam sputtering in an O2 environment. Oxygen ions with 1000 eV energy were formed in a thruster and bombarded a high purity Ti target. The molecules of TiO2 were deposited on a Si (100) wafer at various substrate temperatures. The structural and optical properties were analyzed using Fourier Transform Infrared Spectroscopy in the range of 400-4000 cm-1. An ellipsometer was used to measure the thickness and refractive index of the deposited films. In order to determine the dielectric constant and capacitance of the deposited TiO2, the electrical properties were studied using an MOS capacitor. The effects of substrate temperature and deposition time on the dielectric properties of TiO2 are discussed.Conference Object Citation - WoS: 2Citation - Scopus: 2Microstructural and Electrical Characterization of Ti and Mg Doped Cu-Clad Mgb2 Superconducting Wires(National Institute of Optoelectronics, 2005) Okur, Salih; Kalkancı, Mihriban; Yavaş, Mert; Eğilmez, Mehmet; Özyüzer, LütfiThe recent studies on Ti doping effect on the critical current density (Jc) of MgB2 composite superconductors prepared under ambient pressure has shown an important enhancement at 20 K. In the present work, we have fabricated Ti and Mg doped superconducting MgB2 wires by packing reacted MgB2 and Ti or Mg powders together inside Cu tubes with a diameter of 6 mm. The tubes were then cold worked by rolling or drawing to smaller diameters. The prepared Cu-clad Ti and Mg added MgB 2 superconducting wires were annealed at various temperatures to enhance the grain connectivity of the MgB2 bulk materials. The effect of the sintering time has been investigated for high performance characteristics of superconducting Cu-clad Ti and Mg added MgB2 wires. The microstructural evaluation of the superconducting wires has been carried out using XRD and SEM equipped with EDX analysis system. The interfacial properties between Cu sheath and superconducting core was characterized using SEM-EDX. Furthermore, the influence of the presence of Ti and Mg on Tc has been investigated to understand the structural and electronic properties of superconducting Ti and Mg doped MgB2 wires.Conference Object Citation - WoS: 3Citation - Scopus: 3Light Induced Degradation of Hydrogenated Amorphous Silicon - Germanium Alloy (a-Sige:h) Thin Films(National Institute of Optoelectronics, 2005) Dönertaş, M. Elif; Güneş, MehmetHydrogenated amorphous silicon germanium alloy thin films prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) with varying Germanium concentrations have been investigated in both the annealed and the light soaked state. Samples were characterized using steady state photoconductivity and dual beam photoconductivity (DBP). The Staebler-Wronski effect has been investigated by monitoring the changes in the photoconductivity, σ ph, and the increase in the sub-bandgap absorption coefficient, α. The kinetics of defect creation for different germanium contents has also been compared with those for unalloyed hydrogenated amorphous silicon films. It is found that for the films with low Ge fraction, both a decrease in the photoconductivity and an increase in α (1.0eV) show similar time dependences to those observed in a-Si:H films. However, as the Ge content increases, σ ph degrades faster and the same time dependence is not seen in the increase of α(1.0eV).Conference Object Citation - WoS: 2Citation - Scopus: 3The Effects of Oxide Thickness on the Interface and Oxide Properties of Metal-Tantalum Pentoxide-Si (mos) Capacitors(National Institute of Optoelectronics, 2005) Özdağ, Pınar; Atanassova, Elena; Güneş, MehmetHigh dielectric constant tantalum-pentoxide insulating layers were prepared on p-type (100) crystalline silicon wafers using an RF magnetron sputtering technique. Then, metal-oxide-semiconductor (Al-Ta 2O 5-Si) structures were formed with various oxide thickness from 15 to 25 nm. Devices were characterized using the high frequency capacitance-voltage (C-V) spectroscopy method. From the analysis of the high frequency C-V curves, non-ideal effects such as oxide charges and interface trap densities have been evaluated. The results for Ta 2O 5 layers have been compared with those for conventional SiO 2 layers. Interface trap densities were found to be 1.6 ± 0.4×10 12 eV -1 cm -2 for Ta 2O 5 and about 2×10 11 eV -1 cm -2 for SiO 2 insulating layers. There was no clear thickness dependence of the interface trap densities for the Ta 2O 5 insulating layers.