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Öğe Quantum coherence resourced by the strong nuclear quadrupolar interaction(IOP Publishing Ltd, 2023) Çakmak, Selçuk; Gençten, Azmi; Altıntaş, FerdiWe propose a setup for studying the quantum coherence properties of a quadrupolar nucleus using the nuclear magnetic resonance platforms We consider powder samples labeled with 23Na and oriented with respect to the static magnetic field. By using the l 1-norm of coherence, we examine the quantum coherence in the Zeeman basis at thermal equilibrium. Non-zero coherence is found to result from the strong nuclear quadrupolar spin interactions. It is also shown that higher coherence is created as the quadrupolar interaction coefficient increases. We also discuss the stability of coherence in a possible measurement process in order to use it as a potential resource in any quantum computation protocol.Öğe Investigation of hybrid wires combining superconductive MgB2 and ultra-conductive Graphene/Cu sheath(Elsevier Science Sa, 2024) Karaboğa, Fırat; Farhangmehr, Mojtaba; Özmen, Ahmet; Yetiş, Hakan; Belenli, İbrahim; Ertuğrul, MehmetIn our study, hybrid wires with ultra-conductive Graphene/Copper(GCu) sheath and superconducting MgB2 core were produced and experimentally examined. Cu tubes with outer/inner diameters of 15/12 mm were first coated with multi-layered graphene by chemical vapour deposition (CVD) method. Then, the ultra-conductive G/ Cu tubes were filled with Mg+ 2B powder and they were gradually drawn into wires with a diameter of 1.94 mm. According the analysis results, the graphene coating process was successfully completed and the hybrid wires were produced by achieving MgB2 superconducting phase formation after annealing at 650 circle C for 1 h. In this study, a graphene-coated copper tube with a CVD process was used for the first time to manufacture a superconducting wire. The ampacity value of industrial G/Cu sample has been improved in hybrid wires about 75% despite Cu exposed to mechanical deformations throughout the wire production process after graphene coating.Öğe Graph-based algorithm for the understanding of failures in the ATLAS infrastructure(IOP Publishing, 2023) Uribe, Gustavo A.; Tortajada, Ignacio Asensi; Sanchez, Carlos Solans; Rummler, Andre; Oyulmaz, Kaan Yüksel; Denizli, HalukThe ATLAS Technical Coordination Expert System is a knowledge-based application which describes and simulates the ATLAS experiment based on its components and their relationships with differing levels of granularity but with an emphasis on general infrastructure. It facilitates the sharing of knowledge and improves the communication among experts with different backgrounds and domains of expertise. The developed software has become essential for the planning of interventions as it gives easily insight into their consequences. Furthermore, it has also proven to be useful for exploring the most effective ways to improve the ATLAS operation and reliability by identifying points of failure with significant impact. The underlying database describes more than 13,000 elements with 89,000 relationships among them. It combines information from diverse domains such as detector control and safety systems, gas and water supplies, cooling, ventilation, cryogenics, and electricity distribution. As the most recent addition, a tool to identify the most probable cause of a failure state has been developed. This paper discusses the graph-based algorithm currently implemented by that tool and shows its behaviour based on the parameters entered by the user. An example in form of a real failure event is given which demonstrates the potential of the Expert System for understanding major failures faster in urgent situations.Öğe Performance improvement of GaN-based microdisk lasers by using a PEALD-SiO2 passivation layer(Optica Publishing Group, 2023) Zhao, Hanru; Feng, Meixin; Liu, Jianxun; Sun, Xiujian; Li, Yongjian; Yılmaz, ErcanDry-etching is often utilized to shape GaN-based materials. However, it inevitably causes plenty of sidewall defects as non-radiative recombination centers and charge traps that deteriorate GaN-based device performance. In this study, the effects of dielectric films deposited by plasma-enhanced atomic layer deposition (PEALD) and plasma-enhanced chemical vapor deposition (PECVD) on GaN-based microdisk laser performance were both investigated. The results demonstrated that the PEALD-SiO2 passivation layer largely reduced the trap-state density and increased the non-radiative recombination lifetime, thus leading to the significantly decreased threshold current, notably enhanced luminescence efficiency and smaller size dependence of GaN-based microdisk lasers as compared with the PECVD-Si3N4 passivation layer.Öğe Annealing-induced modifications on structural, surface chemical bonding, and electrical characteristics of p-NiO/n-TiO2 heterostructure(Springer, 2023) Kaya, Şenol; Soykan, Uğur; Sunkar, Mustafa; Karaboğa, Seda; Doğan, Muhsin Uğur; Terzioğlu, Rıfkı; Yıldırım, Gürcan; Terzioğlu, CabirThe influences of annealing temperatures on the electrical characteristics of a p- NiO/n-TiO2 heterojunction diode were thoroughly investigated, taking into account changes in microstructure, morphology, and surface chemistry of the p-NiO/n-TiO2 films, which were deposited on an insulating SiO2/ Si layer. During different annealing processes, considerable stress variations were observed in the p-NiO/n-TiO2 films due to the crystalline evolution of p-NiO and n-TiO2. Notably, the crystallization of the TiO2 layer, which serves as the intermediary between the back contact materials and NiO, led to the evident formation of grain structures. As the annealing temperature increased, the surface roughness also grew from 5.4 to 8.7 nm. At an annealing temperature of 500 degrees C, the formation of a parasitic NiTiOx phase was observed, particularly at the interface between NiO and TiO2. Conversely, the study also revealed that annealing temperature played a significant role in the rectifying behavior, barrier potential, and ideality factor of the diode. Among the various annealing processes, the most favorable results were achieved after annealing at 400 degrees C. At this temperature, the diode demonstrated the lowest ideality factor of 1.89, accompanied by superior rectifying behavior and a barrier potential of 0.70 eV. The findings clearly indicate that any alterations in the surface chemistry and microstructure of the film directly impact the diode's characteristics. Thus, optimizing the annealing temperature becomes crucial for enhancing the performance of the p-NiO/n-TiO2 heterojunction diode.Öğe Development of modulation, pairing mechanism, and slip system with optimum vanadium substitution at Bi-sites in Bi-2212 ceramic structure(Elsevier Science Sa, 2023) Ülgen, Asaf Tolga; Okur, Semih; Erdem, Ümit; Terzioğlu, Cabir; Yıldırım, Gürcan; Turgay, TahsinPresent study focuses extensively on the change in electrical, superconducting and microhardness parameters with partial substitution of trivalent V+3 impurities replacing Bi+3 ions in Bi-2212 ceramic compound with the aid of dc electrical resistivity and microhardness test measurements. Experimental findings, calculation results, and phenomenological discussions provide that the optimum vanadium substitution level is found to be x = 0.01 in the Bi2.0-xVxSr2.0Ca1.1Cu2.0Oy (Bi-2212) ceramic system for the highest conductivity, crystallinity quality, superconducting, and mechanical performance features depending on the decreased microscopic structural problems. All the findings are wholly verified by scanning electron microscopy (SEM) and X-Ray diffraction (XRD) analyses. The dc electrical measurements indicate that the optimum vanadium ions support the pairing mechanism for the formation of new polaronic states in the clusters of microdomains, and hence expand superconducting energy gap due to the enhancement of amplitude part of pair wave function in the spin-density wave systems. The excess vanadium content degrades all the basic thermodynamics and quantum mechanical quantities mentioned due to the stress-induced phase transformation. Numerically, the Bi-2212 advanced ceramic matrix prepared by the optimum vanadium impurity is noticed to present the smallest residual resistivity value of 0.08 m & omega; cm, room temperature resistivity value of 8.84 m & omega; cm, and broadening degree of 0.36 K. Similarly, the ceramic material is found to possess the highest residual resistivity ratio of 3.05, carrier concen-tration number of 0.153041, critical transition offset and onset value of 84.66 K and 85.02 K, respectively. Besides, the microhardness findings reveal that the same compound with the least sensitivity to the applied test loads exhibits the largest Hv value of 4.799 GPa, Young's moduli of 393.303 GPa, yield strength of (0.969 GPa), and elastic stiffness coefficient of 15.5574 (GPa)7/4 under the applied test load of 0.245 N. The XRD in-vestigations show that the presence of optimum vanadium impurity supports the formation of a high super-conducting phase, c-axis length, and average crystallite size. All the findings are morphologically confirmed by the SEM images. It is found that the crystallographically best crystallinity quality and view of surface morphology is observed for the optimum vanadium substitution level. All in all, new higher properties for the conductivity, crystallinity quality, surface morphology, superconducting, and microhardness parameters based on the optimum vanadium replacement encourage the Bi-2212 crystal system to use in much more application places.Öğe Quantum coherence and non-Markovianity in a noisy quantum tunneling problem(Springer, 2023) Mahdi, Nisreen Mohammed; Kurt, Arzu; Altıntaş, FerdiWe investigate the coherence and non-Markovianity of a quantum tunneling system whose barrier is fluctuated by a telegraph noise, and its energy gap is modulated by Gaussian noise. With the help of averaging method, the system dynamics are analytically derived, and the analytical expression for coherence measure and non-Markovianity, focusing on a narrow range of parameter regimes for both initially coherent and non-coherent states are obtained. We observe non-Markovian dynamics in a situation where the Kubo number is high. It is also found that there is no strong relation between the coherence of the system and non-Markovian dynamics except a region in which these two tend to change their behavior at the intermediate noise color for two initial states.Öğe MALTA monolithic pixel sensors in TowerJazz 180 nm technology(Elsevier, 2023) Sanchez, C. Solans; Allport, P.; Denizli, Haluk; Berlea, D. V.; Oyulmaz, Kaan Yüksel; Bortoletto, D.Depleted Monolithic Active Pixel Sensors are of highest interest at the HL-LHC and beyond for the replacement of the Pixel trackers in the outermost layers of experiments where the requirement on total area and cost effectiveness is much bigger. They aim to provide high granularity and low material budget over large surfaces with ease of integration. Our research focuses on MALTA, a radiation hard DMAPS with small collection electrode designed in TowerJazz 180 nm CMOS imaging technology and asynchronous read-out. Latest prototypes are radiation hard up to 2 x 1015 1 MeV neq/cm2 with a time resolution better than 2 ns.Öğe Radiation hardness of MALTA2, a monolithic active pixel sensor for tracking applications(IEEE-Inst Electrical Electronics Engineers Inc., 2023) Denizli, Haluk; Berlea, D. V.; Allport, P.; Tortajada, I. Asensi; Bortoletto, D; Buttar, C.MALTA is a depleted monolithic active pixel sensor (DMAPS) developed in the Tower Semiconductor 180-nm CMOS imaging process. Monolithic CMOS sensors offer advantages over current hybrid imaging sensors in terms of both increased tracking performance due to lower material budget and ease of integration and construction costs due to the integration of read-out and active sensor into one ASIC. Current research and development efforts are aimed toward radiation hard designs up to 100 Mrad in total ionizing dose (TID) and 1 x 10(15) 1 MeVn(eq)/cm(2) in nonionizing energy loss (NIEL). The design of the MALTA sensors was specifically chosen to achieve radiation hardness up to these requirements and satisfy current and future collider constraints. The current MALTA pixel architecture uses small electrodes which provide less noise, higher signal voltage, and a better power-to-performance ratio. To counteract the loss of efficiency in pixel corners, modifications to the Tower process have been implemented. The MALTA sensors have been tested during the 2021 and 2022 SPS CERN Test Beam in the MALTA telescope. The telescope ran for the whole duration of the beam time and took data to characterize the novel MALTA2 variant and the performance of irradiated samples in terms of efficiency and cluster size. These campaigns show that MALTA is an interesting prospect for HL-LHC and beyond collider experiments, providing both very good tracking capabilities and radiation hardness in harsh radiation environments.Öğe MALTA-Cz: a radiation hard full-size monolithic CMOS sensor with small electrodes on high-resistivity Czochralski substrate(IOP Publishing Ltd, 2023) Pernegger, H.; Allport, P.; Berlea, D. V.; Birman, A.; Bortoletto, D.; Denizli, HalukDepleted Monolithic Active Pixel Sensor (DMAPS) sensors developed in the Tower Semiconductor 180 nm CMOS imaging process have been designed in the context of the ATLAS ITk upgrade Phase-II at the HL-LHC and for future collider experiments. The "MALTA-Czochralski (MALTA-Cz)" full size DMAPS sensor has been developed with the goal to demonstrate a radiation hard, thin CMOS sensor with high granularity, high hit-rate capability, fast response time and superior radiation tolerance. The design targets radiation hardness of > 10(15) (1 MeV) n(eq)/cm(2) and 100 Mrad TID. The sensor shall operate as tracking sensor with a spatial resolution of approximate to 10 mu m and be able to cope with hit rates in excess of 100 MHz/cm(2) at the LHC bunch crossing frequency of 40 MHz. The 512 x 512 pixel sensor uses small collection electrodes (3.5 mu m) to minimize capacitance. The small pixel size (36.4 x 36.4 mu m(2)) provides high spatial resolution. Its asynchronous readout architecture is designed for high hit-rates and fast time response in triggered and trigger-less detector applications. The readout architecture is designed to stream all hit data to the multi-channel output which allows an off-sensor trigger formation and the use of hit-time information for event tagging.The sensor manufacturing has been optimised through process adaptation and special implant designs to allow the manufacturing of small electrode DMAPS on thick high-resistivity p-type Czochralski substrate. The special processing ensures excellent charge collection and charge particle detection efficiency even after a high level of radiation. Furthermore the special implant design and use of a Czochralski substrate improves the sensor's time resolution. This paper presents a summary of sensor design optimisation through process and implant choices and TCAD simulation to model the signal response. Beam and laboratory test results on unirradiated and irradiated sensors have shown excellent detection efficiency after a dose of 2 x 10(15) 1 MeV n(eq)/cm(2). The time resolution of the sensor is measured to be sigma = 2 ns.Öğe Sensitivity of anomalous quartic gauge couplings via tri-photon production at FCC-hh(Elseiver, 2024) Şenol, Abdulkadir; Denizli, Haluk; Helveci, CerenA direct investigation of the self-couplings of gauge bosons, completely described by the non-Abelian gauge symmetry of the Standard Model, is extremely valuable in understanding the gauge structure of the SM. Any deviation from the SM predictions on gauge boson self-coupling is to give a hint at the existence of a new physics beyond the SM, which is defined with a modification of the self-interactions using an effective field theory approach. In this paper, we present a detailed Monte Carlo study searching for anomalous quartic gauge dimension-8 couplings related to yyyy and yyyZ vertices at the future hadron-hadron collider (FCC-hh) via tri-photon production at a 100 TeV center of mass energy with an integrated luminosity L1,,, =30 ab-1. Events that have been parton showered and include detector effects are analyzed with a Toolkit for Multivariate Data Analysis (TMVA) using a boosted decision tree to help distinguish between signal and background events to achieve the best sensitivities on anomalous quartic gauge couplings. Our obtained results reveal that the limits on anomalous quartic gauge couplings fT 8/Lambda 4 and fT 9/Lambda 4 at 95% C.L. without systematic errors are about three orders of magnitude stronger compared to the best current experimental limits reported by the ATLAS collaboration at the LHC. Considering a realistic systematic uncertainty such as 10% from possible experimental sources, our obtained limits of anomalous quartic couplings get worse by about one order of magnitude compared to those without systematic uncertainty but are still two orders of magnitude better than those recently reported by ATLAS.Öğe ?-? phase transition of elemental cerium metal(IOP Publishing Ltd, 2022) Eryiğit, Serpil; Parlak, Cihan; Eryiğit, ResulThe isostructural gamma-alpha phase transition in elemental cerium has been the subject of many experimental and theoretical studies over almost the past century without a universally agreed upon mechanism. here, we report the results of an extensive study of electronic and magnetic structures, f-electron number, entanglement entropy, and elastic properties of cerium in the GGA + U framework. We have found that almost all changes in the studied quantities mimic their behavior in the phase transition and could be related to the symmetry of the 4f occupation and the small change in Hubbard U near a critical value.Öğe Investigation of hole-doping effect on structural, magnetic properties and magnetoresistance via Gd-site substitution by Pb in the layered manganite La0.1Gd0.2-xPbxCa1.2Sr0.6Mn2O7 (0 <= x <= 0.2)(Springer, 2023) Belguet, Radjia; Mahamdioua, Nabil; Meriche, Faiza; Alonso, Jose A.; Martinez, Jose L.; Altıntaş, Sevgi Polat; Terzioğlu, CabirIn this work, the hole-doping double-layered manganites with formula La1:0Gd(0.2-x)PbxCa1.2Sr0.6Mn2O7 (x = 0, 0.1, and 0.2) are prepared by the solidstate reaction route and experimentally characterized. The samples' crystallization into a tetragonal structure with an I4/mmm space group was confirmed by Rietveld refinement results of the XRD diffraction patterns using the FullProf software. The results were thoroughly studied after it was discovered that the cell parameters were decreasing. The structure was granular and porous, with grains that resembled spheres, according to micrographs obtained using a scanning electron microscope (SEM). Fourier-transform infrared (FTIR) analysis shows that our samples' characteristic vibrational bands are present. The entire temperature range of 0 to 300 K was used to evaluate electrical resistivity both in the absence and in the presence of an applied magnetic field. The increase in bandwidth, which is determined from the Rietveld refinement results, is found to explain why the rho(T) lowers with increasing Pb concentrations for a given temperature. The calculated magnetoresistance (MR%) for sample with x = 0.1 fell to 24.62% at 8 K for x = 0.2 from a maximum value of 30.01% at 5 K under 1 T of applied magnetic field. These values give our samples the opportunity to be good candidates in temperature and magnetic sensors in the cryogenic domains at low magnetic field. Residual resistivity, weak localization, electronelectron, and/or electron-phonon combinations fit the resistivity curves well in the low temperature region. The resistivity curves' fitting revealed that the adiabatic tiny polaron hopping model and Mott's 3D variable range hopping mechanism (3D-VRH) are both effective at controlling electrical conduction above T-MI and below Debye temperature, respectively. Based on Mott's 3D-VRH model, the density of states near the Fermi level (DOS), mean hopping distance Rh, and mean hopping energy E-h of the charge carriers have been carried out and discussed. On the basis of measurements of magnetization, inverse susceptibility, and loop hysteresis, the samples' magnetic properties are thoroughly described and discussed. The samples show a magnetic phase change from the ferromagnetic to the paramagnetic phase at Curie temperature T-C. Griffith phase temperature was determined to be above T-C based on the inverse of susceptibility's temperature dependency.Öğe Addition effects of MgO on structure and physical roperties in Bi-2212 ceramics(International Information and Engineering Technology Association, 2022) Kalkoul, Nadira; Boussouf, Nora; Mahjoub, Saadia; Sahraoui, Hadda; Mosbah, Mohamed Faycal; Altıntaş, Sevgi Polat; Koç, Nevin SoyluThe effect of magnesium on the microstructural and superconducting characteristics of bulk Bi2Sr(2)CaCu(2)MgxOy superconductors with x=0 to 0.05 by solid reaction has been examined in this study. Bi2Sr(2)CaCu(2)O(8+)(d) is formed as the primary phase, and Bi2Sr2CuO8+d (Bi-2201) is present as the parasitic phase, according to XRD data. In doped samples, the c lattice parameter decreases, indicating that Mg has entered the Bi2Sr(2)CaCu(2)O(8+)(d) crystallographic unit cell. The grain morphology of the samples containing magnesium has changed significantly, and the lamellar structure typical of high temperature superconductors can be seen in the SEM micrographs. The critical temperatures, T-coff and Tconset, are raised by the addition of Mg, delimiting the superconductive transition. Tconset's maximum value corresponds to x = 0.05.Öğe Evolution of operable slip systems, lattice strain fields and morphological view of Bi-2223 ceramic system with optimum NiO addition(Elsevier, 2023) Mercan, Ali; Kara, Emre; Doğan, Muhsin Uğur; Kaya, Şenol; Terzioğlu, Rıfkı; Erdem, Ümit; Yıldırım, Gürcan; Terzioğlu, CabirThe current work extensively reveals the influence of different nickel oxide (NiO) impurity addition levels on the morphological, microstructural, key mechanical performance, and mechanical characteristic properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Oy (Bi-2223) ceramics using scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and Vickers micro-indentation (Hv) hardness measurements. It was observed that the addition of NiO impurity in the Bi-2223 crystal structure affected seriously the fundamental characteristic features. In the case of the optimum NiO concentration level of x = 0.1, the Bi-2223 materials exhibited the best crystallinity quality and coupling strengths between the adjacent layers, the most uniform surface view, and the densest, and the smoothest crystal structure. Similarly, the compound was noted to possess the hardest, highest mechanical strength, durable tetragonal phase, resistance toward failure by fatigue, and elastic recovery properties. Besides, it was observed that the characteristic Bi-2223 superconducting phase fraction and stabilization of the tetragonal crystal system reached the maximum level for the optimum concentration. Moreover, optimum NiO particles brought about a considerable increase in the number of operable slip systems, surface residual compressive force regions, and lattice strain fields. Correspondingly, the mobility of defects was blocked significantly depending on the preference of defects through transcrystalline regions. Additionally, optimum addition strengthened the typical indentation size effect due to the improvement of the recovery mechanism. In this regard, the NiO-added sample exhibited the least response to the applied loads. Thus, the Bi-2223 sample with the optimum NiO concentration was found to present the highest hardness parameter of 0.496 GPa, greatest elastic deformation value of 16.493 GPa, largest stiffness value of 1.044 MN/m, and smallest contact depth of 5.849 mu m. On the other hand, after the optimum concentration level of x = 0.1, there appeared serious increase in problems including internal defects, impurity residues, microscopic structural problems, and connection problems between the grains. All experimental findings were theoretically supported by semi-empirical mechanical methods. To sum up, the addition of NiO particles was noticed to increase the potential application areas of Bi-2223 ceramicÖğe Enhanced breakdown voltage and dynamic performance of GaN HEMTs with AlN/GaN superlattice buffer(IOP Publishing Ltd, 2023) Chen, Xin; Zhong, Yaozong; Yan, Shumeng; Guo, Xiaolu; Gao, Hongwei; Yılmaz, ErcanThe characteristics of an AlGaN/GaN high-electron-mobility transistor buffer structure are studied and optimized by employing an AlN/GaN superlattice (SL) structure. Through vertical leakage analysis and back-gate measurement, combined with Silvaco-TCAD simulation, the influence of buffer trapson the carrier transport behaviors and electrical performance for SL buffer structures under a high electric field is analyzed. The AlN/GaN SL buffer structures are further optimized with various AlN/GaN thickness ratios and their total thickness through both simulation and experimental studies. As a result, a high breakdown voltage of up to 1.3 kV with a maximum breakdown electric field of 2.8 MV cm(-1) has been achieved. Moreover, the buffer trapping effect is dramatically suppressed, leading to a minimum drop of channel current for the optimized sample, in which donor traps are found to play a positive role in the device dynamic characteristics.Öğe Enhancing magnetoresistive features of iron-substituted La0.8Sr0.2MnO3 ceramic manganites(Elsevier Sci LTD, 2022) Karadavut, Samed; Denbri, Fatih; Terzioğlu, Cabir; Öztürk, Özberk; Altıntaş, Sevgi PolatThe influence of iron content on the structural, microstructural, magnetic, and electrical-transport features of the ceramic perovskite manganites of the form La0.8Sr0.2Mn1-xFexO3 (x=0.0, 0.05, 0.1, and 0.2) was investigated. A single phase of rhombohedral-distorted structure with an R c space group was confirmed for all synthesized ceramic samples. The microstructures of the manganite ceramics were improved by iron substitution. The magnetic and electrical-transport studies show that samples with x=0.0, 0.05, and 0.1 display phase transitions from ferromagnetic to paramagnetic state and metallic to insulating one with increasing temperature. The phase transition temperatures, i.e., Curie temperature, TC, and the resistance transition temperature TMI, are found to be lowered with the increase in the Fe concentration. The temperature coefficient of resistance (TCR) value for the x=0.0 sample is obtained similar to 2.16% K-1 and slightly decreased to similar to 1.55% K-1 with a 5% Fe substituted sample. As x rise to 0.1, we obtain the maximum TCR value of similar to 8.23% K-1. At the same time, the maximum magnetoresistance is obtained as 48.1% at 233 K for the x=0.1 sample. One of the most important findings in this paper is that Fe substitution is very useful for improving magneto-electrical features of the La0.8Sr0.2MnO3 ceramics. Moreover, to better understand the temperature dependence of the electrical resistivity data, the experimental findings were fitted to the equations of several models.Öğe Improvement in deformation degree of Zr surface-layered Bi-2223 ceramics by diffusion annealing temperature(Elsevier Sci LTD, 2023) Mercan, Ali; Terzioğlu, Rıfkı; Doğan, Muhsin Uğur; Kaya, Şenol; Erdem, Ümit; Yıldırım, Gürcan; Terzioğlu, Cabir; Varilci, AhmetThis study investigated the effects of different annealing temperatures (650 degrees C <= T <= 840 degrees C) on the surface morphological and mechanical performance properties of Zr surface-layered Bi-2223 materials with scanning electron microscopy (SEM) images, Vickers microhardness (Hv) measurements, and semi-empirical mechanical approaches. It was observed that the ceramic compound exposed to 650 degrees C annealing temperature exhibited the superior performance features due to the enhancement in the deformation degree. This is because the Zr ions behaved as the nucleation centers to prevent the propagations of cracks and dislocations throughout the main matrix depending on the decrease in the degree of granularity and distributions of crystal structure problems over a wider area. Similarly, the SEM pictures indicated that the diffusion mechanism increased the random distributions of the thinner plate-like granular structures (serving as nucleation centers), leading the decrease in the coupling problems between the grains. Among the materials, the highest surface densification was observed for the compound exposed to 650 degrees C. Namely, surface morphological analysis showed a strong correlation be-tween microstructure and mechanical performances. Further, the zirconium ions were found to decrease in the non-recoverable stress concentration sites, crack-initiating defects, and dislocations in the ceramic system. Accordingly, the sensitivity to the applied test load was noted to decrease dramatically. Shortly, crack growth size and velocity were observed to be more easily under control. Correspondingly, the Zr ions delayed consid-erably the beginning points of saturation limit (load-independent) regions for the bulk Bi-2223 superconducting materials. Additionally, the Zr ions led to the change in the mechanical characteristic behavior from typical indentation size effect to reverse indentation size effect. Lastly, the microindentation hardness measurements were semi-empirically analyzed by the different models. According to the comparison, Hays-Kendall mechanical model was noted to provide the closest parameters to the load-independent microhardness results.Öğe Current-voltage characteristics of nano whisker ZnO/Si heterojunction under UV exposition(Elsevier Science Sa, 2022) Koç, Nevin Soylu; Altıntaş, Sevgi Polat; Gökçen, Muharrem; Doğruer, Musa; Altuğ, Cevher; Varilci, AhmetIn/ZnO/p-Si heterojunction diode was produced to investigate the photo-responsivity and electrical features under ultraviolet (UV) light. A hydrothermal synthesis technique was used to coat the ZnO layer on the p-Si single crystal as nanowhisker/rods. The formation of surface and nanowhisker properties of the ZnO layer were investigated by scanning electron microscope (SEM). The I-V (current-voltage) analysis of the In/ZnO/p-Si diode was realized in dark and under UV (290-400 nm) illumination. Further, the main electrical parameters of the diode; such as reverse bias saturation current (I-V), ideality factor (n), zero bias barrier height (Phi(Bo)), resistance (R) and interface state density (N-ss) were obtained from the experimental I-V measurements by thermionic emission (TE) and Card and Rhoderick's function. Also, the power law of the photocurrents (I-PC), photoresponsivity (PR) and response time were extracted. Photo-responsivity and response time values of In/ZnO/p-Si heterojunction diode were obtained as 2.0 A/W and (rise/decay) 160/200 ms, respectively.Öğe Effect of high-radiation-dose-induced structural modifications of HfSiO4/n-Si on electrical characteristics(Pergamon-Elsevier Science Ltd, 2022) Kahraman, Ayşegül; Mutale, Alex; Lök, Ramazan; Yılmaz, ErcanHigh-k/n-Si structures were formed with HfSiO4 films annealed at the temperature range of RT (room temperature)-900 degrees C and radiation-induced structural modifications were determined by XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy) techniques in the study. The effect of oxygen-deficient bond contents on the electrical characteristics of HfSiO4 pMOS (n type Metal Oxide Semiconductor) capacitors whose radiation response was investigated in the 0-50 kGy dose range was investigated. While no XRD peak was observed before and after irradiation at RT and 500 degrees C-HfSiO4/n-Si, crystallization started with irradiation at 900 degrees C. The dielectric constant of the film was found in the range of 16-23. It was determined that Hf-Hf oxygen-deficient bonds act as negative charge trapping centers, while Hf-Si and Si-Si oxygen-defective bonds act as positive charge trapping centers. The direction of the C-V (Capacitance-Voltage) curve changed continuously with increasing radiation dose. The change in the interface trap charge density was found to be higher than the change in the oxide trap charge density for all doses in RT-HfSiO4 pMOS capacitor and for 1 kGy at 500 degrees C-HfSiO4 pMOS capacitor. Oxygen defective bond content and Hf-O-Si/Si-O-Si ratios were sufficient to establish a link between structural analyses and electrical characteristics at some doses. In some cases, the frequency-dependent charges had a more dominant effect on the radiation response of the device compared to the oxide trap charges.
