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: 1Selection of the Best Proper Dc-Squids in a Multi-Squid Configuration(IEEE, 2007) Avcı, İlbeyi; Akram, R.; Bozbey, Ali; Tepe, Mustafa; Abukay, DoğanWe have carried out experimental investigation of multi-DC-SQUID magnetometer configuration fabricated on YBa2Cu30 7-δ thin films onto 24 degree SrTiO3 bicrystal substrates by directly coupling the pick-up loop to DC-SQUIDs. The layout of the magnetometer pick-up loop was chosen as a square washer configuration by maximizing loop effective area and minimizing loop inductance. We have used De-Magnetron Sputtering technique for deposition of the films and chemical etching process for patterning the Josephson junctions having 4 μm widths. The use of multi-SQUID configuration is related to the selection of the best proper junctions for SQUID to improve the chip sensitivity with selectivity option of choosing the squid junctions rather than multichannel operation. Selection of the best junctions compared to each other depending on the junction critical currents and noise levels caused by the fabrication process and placements of the junctions on the grain boundary enable having an increased output signal of the DC-SQUID.Article Citation - WoS: 10Citation - Scopus: 12The Superconducting Transition Width and Illumination Wavelength Dependence of the Response of Mgo Substrate Ybco Transition Edge Bolometers(Elsevier Ltd., 2007) Öktem, B.; Bozbey, Ali; Avcı, İlbeyi; Tepe, Mustafa; Abukay, Doğan; Fardmanesh, M.Dependence of the phase and magnitude of the response of MgO substrate YBa2Cu3O7-δ (YBCO) transition edge bolometers to the near infrared radiation on the superconducting transition width is presented in this work. The bolometers were made of YBCO thin films of 200 nm thickness that were grown on single crystal MgO (1 0 0) substrates by DC inverted cylindrical magnetron sputtering. We have measured the responses of both large and small area devices with respect to the bias temperature and radiation modulation frequency. We have observed that the superconducting transition width has major effects on the response of the bolometers such as; on a dip of the phase of the response versus modulation frequency curve around 1 Hz, the rate of decrease of the magnitude of the response, and dependence of the phase of the response on temperature at mid-range modulation frequency. We have investigated a correlation between the superconducting transition width and the YBCO film surface morphology of the devices. In addition, the illumination wavelength dependence of the optical response of both wide and narrow transition width devices has been investigated. Here we present the analysis and the possible mechanisms that can affect the response of the bolometers at the superconducting transition region.Article Citation - WoS: 5Citation - Scopus: 6Effect of Deposition Conditions on Yba2cu3o 7-? Thin Films by Inverted Cylindrical Magnetron Sputtering and Substrate Effects(Elsevier Ltd., 2004) Avcı, İlbeyi; Tepe, Mustafa; Abukay, DoğanThe dependence of YBCO thin film properties on the deposition conditions was studied for different substrates. The deposition conditions were optimized for the epitaxial growth of high quality YBCO thin films of 1500 Å thickness onto single crystal (100-oriented) SrTiO3 (STO), MgO and LaAlO3 (LAO) substrates by DC Inverted Cylindrical Magnetron Sputtering (ICMS). The samples were investigated in detail by means of X-ray diffraction analysis (XRD), EDX, AFM, ρ-T, magnetic susceptibility and current-voltage (I-V) characterizations. The samples show strong diamagnetic behavior and sharp transition temperatures of 89-91 K with ΔT < 0.5 K. XRD of the samples exhibited highly c-axis orientation. The full width at half maximum (FWHM) values of the rocking curves were ranging typically from 0.22 to 0.28°. The samples have smooth surfaces as shown from AFM micrographs. The surface roughness, Ra, changed between 5-7 nm. I-V characteristics were obtained from the 20μm-wide microbridges, which were patterned by a laser writing technique. The critical current densities (Jc, 1.06 × 106 for LAO-based YBCO, 1.39 × 106 for MgO-based YBCO, 1.67 × 106A/cm2 for STO based YBCO) of the microbridges were evaluated from I-V curves at 77 K.Article Citation - WoS: 39Citation - Scopus: 40Investigation of the Variation in Weak-Link Profile of Yba 2cu3-Xagxo7 Superconductors by Ag Doping Concentration(Elsevier Ltd., 2004) Tepe, Mustafa; Avcı, İlbeyi; Koçoğlu, H.; Abukay, DoğanThe effect of Ag doping concentration on the microstructure, transport properties and weak-link profile of YBa2Cu3-xAg xO7-δ bulk superconducting compound was investigated through resistance-temperature (R-T), ac magnetic susceptibility (χ-T), scanning electron microscope (SEM), X-ray diffraction (XRD) and the critical current density (Jc) versus applied magnetic field (Jc-B) measurements. We used the additive method with cationic ratio of x=0.1-0.4 for the YBCO-Ag system. The change in the silver doping concentration slightly affected the transition temperatures (Tc,zero), whereas, the critical current densities (Jc) of the samples and their magnetic field (B) dependencies were noticeably affected. The improvement on the microstructural properties of YBCO bulk superconductors was observed in SEM analysis, the J c values increased and their magnetic field dependencies decreased with the increasing of Ag concentration up to x=0.2. As well as the current transport properties. Ag doping up to a certain amount produces texturing that gives rise to a modification in the weak-link profile resulting in an enhanced strength of flux pinning which causes an increase in the current carrying capacity.Article Citation - WoS: 12Citation - Scopus: 12Effect of Pelletization Pressure on Structural Properties and Critical Current Hysteresis of Ceramic Superconducting Bi1.7pb0.3sr2ca2cu3o Y(John Wiley and Sons Inc., 2003) Tepe, Mustafa; Avcı, İlbeyi; Abukay, DoğanThe effect of pelletization pressures on structural properties and critical current hysteresis of Bi1.7Pb0.3Sr2Ca2Cu3Oy samples was investigated. The samples used in this study were prepared by classical solid-state reaction at the pressures from 100 up to 500 MPa. The obtained samples were characterized by resistance vs. temperature, (R-T), critical current density vs. applied magnetic field, (Jc-H), material density vs. pressure, (ρ-P), XRD, SEM, and ED AX. The results of this study showed that the quality of electrical and structural properties of Bi-2223 bulk superconductors strongly depends on the pelletization pressure. Pressing of bulk samples at 400 MPa produces textured grain alignment and associates micro- structural modifications in order to enhance flux pinning and thus increases current carrying capacities.