Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 171Citation - Scopus: 169Janus Single Layers of In2sse: a First-Principles Study(American Physical Society, 2018) Kandemir, Ali; Şahin, HasanBy performing first-principles calculations, we propose a stable direct band gap semiconductor Janus single-layer structure, In2SSe. The binary analogs of the Janus structure, InS and InSe single layers are reviewed to evince the structural and electronic relation with In2SSe. The structural optimization calculations reveal that a Janus In2SSe single layer has hexagonal geometry like the InS and InSe single layers, which are also its structural analogs. The Janus single layer is dynamically stable, as indicated by the phonon spectrum. The electronic band diagram of the Janus structure shows that an In2SSe single layer is a direct band gap semiconductor, in contrast to its analogs, InS and InSe single layers, which are indirect band gap semiconductors. Nevertheless, it is found that the strain effect on electronic properties of the InS and InSe single layers designates the electronic structure of the Janus single layer. A rough model for the construction of the electronic band diagram of the Janus structures is discussed, and it is indicated that the difference in work functions of chalcogenide sides in the Janus structure determines the construction of the electronic structure. It is found that the Janus structure is a robust direct gap semiconductor under tolerable strain; for that reason, the Janus In2SSe single layer is a candidate for optoelectronic nanodevice applications.Article Citation - WoS: 10Citation - Scopus: 11Single layer PbI2: Hydrogenation-driven reconstructions(Royal Society of Chemistry, 2016) Bacaksız, Cihan; Şahin, HasanBy performing density functional theory-based calculations, we investigate how a hydrogen atom interacts with the surfaces of monolayer PbI2 and how one- and two-side hydrogenation modifies its structural, electronic, and magnetic properties. Firstly, it was shown that the T-phase of single layer PbI2 is energetically more favorable than the H-phase. It is found that hydrogenation of its surfaces is possible through the adsorption of hydrogen on the iodine sites. While H atoms do not form a particular bonding-type at low concentration, by increasing the number of hydrogenated I-sites well-ordered hydrogen patterns are formed on the PbI2 matrix. In addition, we found that for one-side hydrogenation, the structure forms a (2 × 1) Jahn-Teller type distorted structure and the bandgap is dramatically reduced compared to hydrogen-free single layer PbI2. Moreover, in the case of full hydrogenation, the structure also possesses another (2 × 2) reconstruction with a reduction in the bandgap. The easily tunable electronic and structural properties of single layer PbI2 controlled by hydrogenation reveal its potential uses in nanoscale semiconducting device applications.Article Citation - WoS: 60Citation - Scopus: 64Improvement of Optical and Electrical Properties of Ito Thin Films by Electro-Annealing(Elsevier Ltd., 2015) Köseoğlu, Hasan; Türkoğlu, Fulya; Kurt, Metin; Yaman, Mutlu Devran; Akça, Fatime Gülşah; Aygün, Gülnur; Özyüzer, LütfiThe effect of electro-annealing in vacuum and air on the optical and electrical properties of ITO thin films grown by large area DC magnetron sputtering was investigated. Moreover, the performances of the electro-annealed ITO thin films in vacuum and air were compared. Electro-annealing was performed by applying 0.75, 1.00, 1.25 and 1.50 A constant ac current to the ITO thin films. It was observed that the crystallinity of the films was better for the ITO thin films electro-annealed in vacuum. The changes in sheet resistance of electro-annealed ITO thin films with applied currents were detailed. The transmittance of the films increased for both electro-annealing in vacuum and air. A correlation between band-gap and resistivity for all of the electro-annealed thin films was observed.Article Citation - WoS: 12Citation - Scopus: 12High Transmission Through a 90° Bend in a Polarization-Independent Single-Mode Photonic Crystal Waveguide(The Optical Society, 2015) Erol, Adem Enes; Sözüer, Hüseyin SamiWe propose a polarization-independent single-mode waveguide, using a two-dimensional square photonic crystal with a complete band gap. The waveguide is tuned such that both TE and TM modes have the same group velocity and zero group velocity dispersion at the centergap frequency. We also present results for a 90° bend with transmission values of 98% for both modes.Article Citation - WoS: 72Citation - Scopus: 80Electronic, Phononic, and Thermoelectric Properties of Graphyne Sheets(American Institute of Physics, 2014) Sevinçli, Haldun; Sevik, CemElectron, phonon, and thermoelectric transport properties of α-, β-, γ-, and 6,6,12-graphyne sheets are compared and contrasted with those of graphene. α-, β-, and 6,6,12-graphynes, with direction dependent Dirac dispersions, have higher electronic transmittance than graphene. γ-graphyne also attains better electrical conduction than graphene except at its band gap. Vibrationally, graphene conducts heat much more efficiently than graphynes, a behavior beyond an atomic density differences explanation. Seebeck coefficients of the considered Dirac materials are similar but thermoelectric power factors decrease with increasing effective speeds of light. γ-graphyne yields the highest thermoelectric efficiency with a thermoelectric figure of merit as high as ZT-=-0.45, almost an order of magnitude higher than that of graphene.Article Citation - WoS: 31Citation - Scopus: 30Absence of Pseudogap in Heavily Overdoped Bi2sr2cacu2o8+? From Tunneling Spectroscopy of Break Junctions(Institute of Physics Publishing, 2002) Özyüzer, Lütfi; Zasadzinski, John F.; Gray, Kenneth E.; Kendziora, Christopher A.; Miyakawa, NobuakiWe report tunneling spectroscopy of superconductor-insulator-superconductor break junctions on heavily overdoped Bi2Sr2CaCu2O8+δ with Tc = 56 K. At T ≪ Tc, the junction conductances display well-defined quasiparticle peaks at ±2Δ and in some cases a Josephson current at zero bias. Gap values as small as Δ = 10.5 meV have been observed leading to 2Δ/kTc near the BCS limit for dx2-y2 pairing. Temperature dependence of the gap magnitude, Δ(T), follows the BCS relation and both the quasiparticle gap and Josephson current vanish for T > Tc. Above Tc, the tunneling conductance shows a flat background without any indication of a pseudogap near the Fermi level.