Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 2Citation - Scopus: 4Signal Performance of Dc-Squids With Respect To Ybco Thin Film Deposition Rate(Elsevier Ltd., 2009) Avcı, İlbeyi; Algül, Berrin Pınar; Akram, Rizwan; Bozbey, Ali; Tepe, Mustafa; Abukay, DoğanThe signal performances of YBa2Cu3O7-δ (YBCO) direct current superconducting quantum interference devices (DC-SQUIDs) have been investigated as a function of the thin film structure affected by the growth process. YBCO thin films of 200 nm thicknesses were deposited by DC magnetron sputtering using different deposition rates between 1.0 nm/min and 2.0 nm/min onto 24° bicrystal SrTiO3 (STO) substrates. The thin film samples were subsequently analyzed by XRD and AFM in order to determine their crystalline structures and surface morphologies respectively. The 67 pH directly coupled DC-SQUIDs with 4 μm-wide bicrystal Josephson junctions were fabricated, and characterized with respect to their device performances. The variations in the critical current (Ic), the voltage modulation depth (ΔV) and the noise performance of DC-SQUIDs were reported. The SQUIDs having relatively low deposition rate of 1.0 nm/min was observed to have larger voltage modulation depth as well as higher critical current than that of the samples having larger rate of 2.0 nm/min. The better noise performances were observed as the film deposition rate decreases. The results were associated with the thin film structure and the SQUID characteristics.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.Conference Object Citation - WoS: 1Dependence of Josephson Junction Critical Current on the Deposition Rate of Yba2cu3o7-? Thin Films(American Institute of Physics, 2007) Algül, B. P.; Avcı, İlbeyi; Akram, R.; Bozbey, Ali; Tepe, Mustafa; Abukay, DoğanWe have reported the effect of YBa2Cu3O 7-δ (YBCO) thin film deposition rate on the 24 and 30 degree STO bicrystal Josephson junctions critical currents by fabricating series of junctions with different deposition rates. Dependence of YBCO thin film structures on the deposition rate was investigated. We have observed that the critical currents of junctions are strongly affected by the thin film deposition rate.Article Citation - WoS: 2Citation - Scopus: 2Investigation of the Effect of Thermal Cycling on the Device Performance of Yba2cu3o7-? Dc-Squids(IOP Publishing Ltd., 2007) Avcı, İlbeyi; Algül, B. P.; Bozbey, Ali; Akram, R.; Tepe, Mustafa; Abukay, DoğanWe investigated the effect of thermal cycling on the operational performance of YBa2Cu3O7-δ (YBCO) direct current superconducting quantum interference devices (DC-SQUIDs) fabricated onto 24°SrTiO3 (STO) bicrystal substrates. The devices under investigation consist of directly coupled DC-SQUID magnetometer configurations. Thin films having 200nm thicknesses were deposited by dc-magnetron sputtering and device patterns were made by a standard lithography process and chemical etching. The SQUIDs having 4νm-wide grain boundary Josephson junctions (GBJJs) were characterized by means of critical currents, peak-to-peak output voltages and noise levels, depending on the thermal cycles. In order to achieve a protective layer for the junctions against the undesired effects of thermal cycles and ambient atmosphere during the room temperature storage, the devices were coated with a 400nm thick YBCO layer at room temperature. Since the second layer of amorphous YBCO is completely electrically insulating, it does not affect the operation of the junctions and pick-up coils of magnetometers. This two-layered configuration ensures the protection of the junctions from ambient atmosphere as well as from the effect of water molecules interacting with the film structure during each thermal cycle.Article Developing a Trilayer Processing Technique for Superconducting Yba 2cu3o7-? Thin Films by Using Ge Ion Implantation(IOP Publishing Ltd., 2005) Avcı, İlbeyi; Tepe, Mustafa; Öktem, Bülent; Serincan, Uğur; Turan, Raşit; Abukay, DoğanFor making trilayer superconducting devices based on YBa2Cu 3O7-δ (YBCO) thin film processing, we developed a new technique by employing Ge ion implantation. A YBCO thin film of 150 nm thickness having high c-axis orientation and a transition temperature, T c, of 90 K was implanted with 80 keV, 1 × 1016 Ge ions cm-2 at room temperature. By the result of TRIM calculation, Ge ions were found to penetrate into the YBCO thin film approximately 60 nm below the surface of the film, thus leaving the lower part of the film as a superconductor. Upon implantation with Ge ions, the implanted upper part of the sample lost its electrical conductivity and diamagnetism while its original crystalline structure was preserved. The implanted ions we found did not alter the overall crystal structure of the YBCO thin film; this allowed us to grow an epitaxial superconducting upper layer of YBCO on top of the implanted area, leaving no need to use any buffer layer. The superconducting properties of the upper layer were similar to those of the pure YBCO base layer with an increased room temperature resistivity and a lowered Tc (88 K). This process provides an effective method for fabrication of a trilayer HTS device structure.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: 1Citation - Scopus: 1Electrical and Magnetic Properties of Si Ion Implanted Yba 2cu3o7-? Thin Films and Microbridges(Elsevier Ltd., 2004) Avcı, İlbeyi; Tepe, Mustafa; Serincan, Uğur; Öktem, Bülent; Turan, Raşit; Abukay, DoğanFabrication of superconducting bilayer YBa2Cu3O 7-δ (YBCO) thin film structure by Si ion implantation and properties of microbridge patterned on that are presented. YBCO thin film of 150 nm thickness was grown on single crystal (100) SrTiO3 substrate by inverted cylindrical magnetron sputtering. The sample was implanted with 100 keV, 1×1016 Si ions/cm2. Upon implantation with Si, the sample lost its electrical conductivity and diamagnetism while its crystalline structure was preserved after the annealing of the sample. The implanted ions do not alter the overall crystal structure of high temperature superconductor film. This allows the growth of epitaxial superconducting second layer YBCO film on top of the implanted area without using any buffer layer, thus providing an effective method of fabricating multilayer structures. The second layer film and the microbridge patterned by laser writing technique, showed the superconducting properties similar to those of pure YBCO base layer with a reduced critical current density.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.