Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 4Citation - Scopus: 5Enhanced Optoelectronic Properties of Magnetron Sputtered Ito/Ag Multilayers by Electro-Annealing(AVS, 2022) Uyanık, Zemzem; Türkoğlu, Fulya; Köseoğlu, Hasan; Ekmekçioğlu, Merve; Ata, Bengü; Demirhan, Yasemin; Özdemir, Mehtap; Aygün, Gülnur; Özyüzer, LütfiIndium tin oxide/silver/indium tin oxide (ITO/Ag/ITO) multilayers have attracted much attention to fulfill the growing need for high-performance transparent conducting oxide electrodes. To make these transparent multilayers work better, electro-annealing, which is a method of self-heating by electric current, can be effective. Moreover, the effect of current on ITO/Ag/ITO multilayers should be investigated to make sure that electronic devices will be reliable over their lifetime. In this study, ITO/Ag/ITO multilayer electrodes with varying Ag thicknesses were grown by DC magnetron sputtering at room temperature. Structural, optical, and electrical properties of these multilayers were investigated before and after electro-annealing. Measurement results revealed that improved optical transmittance and sheet resistance can be obtained by the optimization of Ag thickness for the as-grown ITO/Ag/ITO layers. The highest figure of merit (FoM) value of 17.37 × 10−3 Ω−1 with optical transmittance of 85.15% in the visible region and sheet resistance of 11.54 Ω/□ was obtained for the Ag thickness of 16.5 nm for as-grown samples. The electro-annealing of as-grown ITO/Ag/ITO multilayers led to improved optical behavior of the multilayer structure over a wide spectral range, especially in the near-infrared range. Electro-annealing also provided an improvement in the crystallinity and sheet resistance of the electrodes. The improvement of the electrical and optical properties of the structure enabled a FoM of 23.07 × 10−3 Ω−1 with the optical transmittance of 86.80% in the visible region and sheet resistance of 10.52 Ω/□. The findings of this work provide proper knowledge of the properties of ITO/Ag/ITO multilayers under electrical current and suggest that the overall performance of the multilayers can be improved by the electro-annealing process.Other Citation - WoS: 1Türkiye’de Lisansüstü Eğitim Üzerine Gözlem ve Öneriler: Inter-university Modeli(2021) Erdem, RecaiTürkiye'deki henüz gelişimini tamamlamamış üniversitelerde de bilimsel ve akademik yeterlilikleri üst düzeyde öğretim üyeleri bulunabilmektedir. Fakat söz konusu üniversitelerdeki hem toplam öğretim üyesi sayısının hem de uluslararası düzeydeki öğretim üyesi oranının düşüklüğü nedeniyle bu üniversitelerdeki lisansüstü eğitiminin yeterli düzeyde olup olmadığı konusu zaman zaman tartışılabilmektedir. Öte yandan, uluslararası düzeydeki öğretim üyesi sayımızın ihtiyacımızın çok gerisinde olması nedeniyle henüz gelişimini tamamlamamış üniversitelerdeki kaliteli öğretim üyesi potansiyelini etkin bir şekilde kullanmamız gerekmektedir. Bu yazıda, üniversitelerimizdeki, özellikle de gelişme sürecindeki üniversitelerimizdeki öğretim üyesi potansiyelini lisansüstü eğitimin kalitesini artırmada etkin bir şekilde kullanmayı amaçlayan inter-university modeli tartışılmaya açılmaktadır. Bu bağlamda, bu makalede önce, ABD, Kanada, Hindistan gibi ülkelerde uygulanmakta olan çeşitli inter-university modellerine değinilmiş ve daha sonra ise Türkiye'nin ihtiyaçları ve şartlarına uygun bir inter-university modelinin ana hatları önerilmiştir.Article Fine-Tuned Spin-3/2 and the Hierarchy Problem(Hindawi Publishing Corporation, 2020) Sargın, OzanIn the past, Kundu et al. and Chakraborty et al. used extra scalar fields to cancel the quadratic divergences in the Higgs mass squared and they determined the mass of the required scalar field. In this work, a spin-3/2 particle has been used in the same manner to nullify the power-law divergences, and it is determined that the mass of the spin-3/2 particle resides in the ball park of the GUT scale.Article Citation - WoS: 4The Synthesis of Ferromagnetic La0.75ca0.25mno3 Nanowires by a Sol-Gel Method(National Institute of Optoelectronics, 2010) Atalay, Funda E.; Yağmur, V.; Atalay, Selçuk; Kaya, Harun; Tarı, Süleyman; Avşar, D.In this study, densely packed La0.75Ca0.25MnO3 (LCMO) nanowires were synthesized within a porous anodic aluminum oxide (AAO) template by means of a sol-gel method using nitrate as raw material and ethylene glycol as the chelating agent. It was observed from measurements of hysteresis curves that the magnetic behavior of the LCMO nanowire arrays was strongly dependent on the pH of the solution. As it has been reported that bulk polycrystalline La0.75Ca0.25MnO3 samples have a Curie temperature of 224 K [1], it is interesting to find that nanowires produced at pH 3 show ferromagnetic properties at room temperatureArticle Citation - WoS: 25Citation - Scopus: 27Symmergent Gravity, Seesawic New Physics, and Their Experimental Signatures(Hindawi Publishing Corporation, 2019) Demir, Durmuş AliThe standard model of elementary particles (SM) suffers from various problems, such as power-law ultraviolet (UV) sensitivity, exclusion of general relativity (GR), and absence of a dark matter candidate. The LHC experiments, according to which the TeV domain appears to be empty of new particles, started sidelining TeV-scale SUSY and other known cures of the UV sensitivity. In search for a remedy, in this work, it is revealed that affine curvature can emerge in a way restoring gauge symmetries explicitly broken by the UV cutoff. This emergent curvature cures the UV sensitivity and incorporates GR as symmetry-restoring emergent gravity (symmergent gravity, in brief) if a new physics sector (NP) exists to generate the Planck scale and if SM+NP is Fermi-Bose balanced. This setup, carrying fingerprints of trans-Planckian SUSY, predicts that gravity is Einstein (no higher-curvature terms), cosmic/gamma rays can originate from heavy NP scalars, and the UV cutoff might take right value to suppress the cosmological constant (alleviating fine-tuning with SUSY). The NP does not have to couple to the SM. In fact, NP-SM coupling can take any value from zero to Lambda SM2/Lambda NP2 if the SM is not to jump from Lambda SM approximate to 500GeV to the NP scale Lambda NP. The zero coupling, certifying an undetectable NP, agrees with all the collider and dark matter bounds at present. The seesawic bound Lambda SM2/Lambda NP2, directly verifiable at colliders, implies that (i) dark matter must have a mass less than or similar to Lambda SM, (ii) Higgs-curvature coupling must be approximate to 1.3%, (iii) the SM RGEs must remain nearly as in the SM, and (iv) right-handed neutrinos must have a mass less than or similar to 1000TeV. These signatures serve as a concise testbed for symmergence.Article Multicolor Photometric Behavior of the Young Stellar Object V1704 Cygni(Bulgarian Acad Sciences, Inst Astronomy, 2018) Ibryamov, Sunay; Semkov, Evgeni; Peneva, Stoyanka; Karadeniz, UğurResults from BV RI photometric observations of the pre-main sequence star V1704 Cyg collected during the time period from August 2010 to December 2017 are presented. The star is located in the star-forming HII region IC 5070 and it exhibits photometric variability in all optical passbands. After analyzing the obtained data, V1704 Cyg is classified as a classical T Tauri star.Article Citation - WoS: 2Citation - Scopus: 2The Synthesis of Super-Hydrophilic and Hard Mgb2 Coatings as an Alternative To Electroless Nickel Coatings(Slovenska Akademia Vied, 2018) Bülbüll, Ferhat; Güney, M.; Jafarpour, SomaiyehIn this study, we report the electroless deposition using an alternative technique for the fabrication of hard and super-hydrophilic MgB2 films. MgB2 films on AZ91 magnesium alloys were prepared using an electroless bath containing magnesium diboride nanopowders, sodium hypophosphite, sodium succinate, sodium acetate, and dimethyl sulfoxide. The electroless deposition was carried out in a bath kept at a bath temperature of 95 degrees C for 60 min. After deposition, the coated samples were annealed at 300 degrees C for 60 min to investigate crystallization, morphology, and the changes in the hardness and wettability. The phase composition, morphology, the hardness, and the contact angle of produced coatings were studied by X-ray diffractometer, scanning electron microscopy, microhardness tester, and contact angle measurement system, respectively. The coatings exhibited a dense and nodular structure with strong grain connections. As-deposited and annealed MgB2 films showed an orientation with the (101) reflection, and the highest hardness value (500 HV0.01) was obtained from the annealed coating. Both synthesized coatings had a super-hydrophilic surface.Article Citation - WoS: 18Citation - Scopus: 17Cnt Incorporated Polyacrilonitrile/Polypyrrole Nanofibers as Keratinocytes Scaffold(Trans Tech Publications, 2019) İnce Yardımcı, Atike; Aypek, Hande; Öztürk, Özgür; Yılmaz, Selahattin; Özçivici, Engin; Meşe, Gülistan; Selamet, YusufPolypyrrole (PPy) is an attractive scaffold material for tissue engineering with its non-toxic and electrically conductive properties. There has not been enough information about PPy usage in skin tissue engineering. The aim of this study is to investigate biocompatibility of polyacrilonitrile (PAN)/PPy nanofibrous scaffold for human keratinocytes. PAN/PPy bicomponent nanofibers were prepared by electrospinning, in various PPy concentrations and with carbon nanotube (CNT) incorporation. The average diameter of electrospun nanofibers decreased with increasing PPy concentration. Further, agglomerated CNTs caused beads and disordered parts on the surface of nanofibers. Biocompatibility of these PAN/PPy and PAN/PPy/CNT scaffolds were analyzed in vitro. Both scaffolds provided adhesion and proliferation of keratinocytes. Nanofiber diameter did not significantly influence the morphology of cells. However, with increasing number of cells, cells stayed among nanofibers and this affected their shape and size. In this study, we demonstrated that PAN/PPy and PAN/PPy/CNT scaffolds enabled the growth of keratinocytes, showing their biocompatibility.Article Citation - WoS: 6Citation - Scopus: 6The Growth of Silver Nanostructures on Porous Silicon for Enhanced Photoluminescence: The Role of Agno3 Concentration and Deposition Time(EDP Sciences, 2019) Çetinel, Alper; Artunç, Nurcan; Tarhan, EnverSilver nanostructures were obtained by using the electrodeposition method on n-type porous silicon (PSi) under different deposition times and concentrations of AgNO3 solutions. The analyses of the structural and photoluminescence properties of PSi/Ag were studied by SEM, XRD and photoluminescence spectroscopy. SEM analysis showed that the shape and size of Ag nanostructures significantly depend on the deposition time and concentration. It was found that spherical nanoparticles and thin Ag dendrites were obtained in short deposition times at 1 and 5 mM AgNO3 concentrations, whereas, Ag complex dendrite nanostructures formed in long deposition times. It was also found that only micro-sized Ag particles were formed at 10 mM. XRD results revealed that the degree of crystallization increases with increasing concentration. Photoluminescence analysis showed that the deposition time and concentration of AgNO3 remarkably affect the PL intensity of PSi/Ag samples. We determined a PL enhancement of similar to 2.7 for the PSi/Ag deposited at 120 s for 1 mM AgNO3. The improved PL intensity of PSi/Ag nanostructures can be explained by the combination of quantum confinement and surface states. PL analyses also indicated that with increasing deposition time and AgNO3 concentrations, the PL intensity of PSi/Ag structures significantly decreases due to the auto-extinction phenomenon.Article Citation - WoS: 6Citation - Scopus: 7Thermally and Optically Tunable Sub-Terahertz Superconducting Fishnet Metamaterial(Elsevier Ltd., 2018) Sabah, Cumali; Mulla, Batuhan; Altan, Hakan; Özyüzer, LütfiIn this paper, a novel fishnet metamaterial structure is designed and analyzed under different material combinations and under different active controlling techniques. The results indicate that, the proposed fishnet metamaterial has a single resonance with double negativity at 0.39 THz when quartz substrate and aluminum is utilized in the design. Moreover, when the metallic parts are replaced with YBCO, the proposed design also exhibits double negativity with a stronger resonance and can be used as a switch between the double negative and single negative modes if the temperature is altered. In addition to these, when substrate (quartz) is replaced with MgO, the resonance shifts from 0.39 THz to 0.26 THz and shows double negativity. Moreover, switching properties under illumination can also be obtained when the silicon is utilized in the design (MgO-YBCO combination). According to these results, it is found that, in the case that the conductivity of silicon exceeds a certain value, the character of the resonance changes from double negative to the single negative mode.