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Öğe Bimetallic two-dimensional PtAg coverage on h-BN substrate: First-principles calculations(Elsevier, 2014) Ersan, F.; Gokoglu, G.; Akturk, E.This paper presents a study on the coverage of PtAg layer on h-BN 2D system using plane-wave pseudopotential method within density functional theory. There emerge interesting electronic and magnetic properties by the coverage of PtAg on h-BN. FM (ferromagnetic) and AFM (antiferromagnetic) states are considered for PtAg. As the most stable configuration, Pt atom is bound to the top site of N and Ag is adsorbed to hollow site in the (2 x 2) coverage with a binding energy about -1.013 eV. While bare h-BN is nonmagnetic semiconductor with a band gap of 4.58 eV, the band gap becomes 0.18 eV with an AFM semiconductor ground state upon coverage of PtAg adlayer. The electronic structure calculations reveal that the electronic band gap of the composite system is controlled by d-states of Pt atom. The material can have possible applications in spintronics and in catalysis with decreased and engineered band gap. (C) 2014 Elsevier B. V. All rights reserved.Öğe Effects of silver adatoms on the electronic structure of silicene(Elsevier Science Bv, 2014) Ersan, F.; Arslanalp, O.; Gokoglu, G.; Akturk, E.This paper presents the adsorption of Ag adatoms on silicene surface using first-principles plane wave calculations within density functional theory. It is obtained that silver adatoms form strong bonds with the silicene yielding significant binding energies. The bare silicene, which is a nonmagnetic semimetal, becomes either nonmagnetic metal or semiconductor depending on the number of adsorbed silver atoms. Because of the charge transfer from adatoms to silicene, bonding and antibonding pi bands crossing linearly at the Fermi level shift 0.35 eV below the Fermi level for both single and trimer Ag adsorption. Ag dimer adsorbed silicene becomes a narrow gap semiconductor with E-g = 0.112 eV. (C) 2014 Elsevier B.V. All rights reserved.Öğe Electronic structure of BSb defective monolayers and nanoribbons(Iop Publishing Ltd, 2014) Ersan, F.; Gokoglu, G.; Akturk, E.In this paper, we investigate two- and one-dimensional honeycomb structures of boron antimony (BSb) using a first-principles plane wave method within the density functional theory. BSb with a two-dimensional honeycomb structure is a semiconductor with a 0.336 eV band gap. The vacancy defects, such as B, Sb, B + Sb divacancy, and B + Sb antisite disorder affect the electronic and magnetic properties of the 2D BSb sheet. All the structures with vacancies have nonmagnetic metallic characters, while the system with antisite disorder has a semiconducting band structure. We also examine bare and hydrogen-passivated quasi-one-dimensional armchair BSb nanoribbons. The effects of ribbon width (n) on an armchair BSb nanoribbon and hydrogen passivation on both B and Sb edge atoms are considered. The band gaps of bare and H passivated A-Nr-BSb oscillate with increasing ribbon width; this property is important for quantum dots. For ribbon width n = 12, the bare A-Nr-BSb is a nonmagnetic semiconductor with a 0.280 eV indirect band gap, but it becomes a nonmagnetic metal when B edge atoms are passivated with hydrogen. When Sb atoms are passivated with hydrogen, a ferromagnetic half-metallic ground state is observed with 2.09 mu(B) magnetic moment. When both B and Sb edges are passivated with hydrogen, a direct gap semiconductor is obtained with 0.490 eV band gap with disappearance of the bands of edge atoms.Öğe Interactions of h-AlN monolayer with platinum, oxygen, and their clusters(Elsevier, 2015) Ersan, F.; Akcay, A.; Gokoglu, G.; Akturk, E.In this paper, we investigate the adsorption properties of single Pt and O atoms, and PtO, Pt2O, and PtO2 clusters on hexagonal AlN monolayer as well as several substitutions in AlN structure. We employ density functional theory to study electronic structure and charge transfers by considering nonmagnetic and ferromagnetic states. PtO and Pt2O adsorbed AlN system has ferromagnetic ground state with 2.00 mu(B) magnetic moment, while PtO2, Pt, and O adsorption lead to nonmagnetic structures. Pt adsorbed AlN system has the lowest adsorption energy with -3.175 eV indicating the most stable structure energetically. Oxygen atom largely disrupts the AlN layer due to strong N-O repulsion caused by high electronegativities of N and O atoms. The substitution of AlN monolayer with Pt and O atoms also presents interesting features. The various substitutions are able to yield ferromagnetic structures with semiconducting (AlO), metallic (N-Pt), or half-metallic (Al-Pt) ground states. These properties can lead to possible applications in spintronics and nanoelectronics. (C) 2015 Elsevier B.V. All rights reserved.Öğe Theoretical investigation of lithium adsorption, diffusion and coverage on MX2 (M = Mo, W; X = O, S, Se, Te) monolayers(Elsevier, 2017) Ersan, F.; Ozaydin, H. D.; Gokoglu, G.; Akturk, E.It is important to improve the high-efficient anode materials for Li batteries, which require the large capacity, high stability and mobility. In this work, we present the adsorption and diffusion properties of lithium atom on MX2 (M = Mo, W; X = O, S, Se, Te) transition metal dichalcogenide structures using first principles calculations within density functional theory. All the MX2 systems considered are semiconductor in bare state with band gaps between 0.93 eV (MoO2) and 1.79 eV (WS2). They turn into metal upon single Li adsorption. Li atom is adsorbed on MoO2 and WO2 rather stronger than other systems. The energy barrier for diffusion of single Li on MX2 varies between 0.15 eV and 0.28 eV which are lower or comparable to that of graphene or silicene. Two Li atoms are preferably adsorbed on MX2 monolayer symmetrically at opposite sides with high adsorption energy. The increasing number of Li atoms does not remarkably affect the adsorption energy per Li atom. This can be attributed to that Li atoms do not accumulate on certain regions of the surface. The systems under investigation provide insights into exploring electronic properties which are rather adequate for possible applications in Li-ion batteries. (C) 2017 Elsevier B.V. All rights reserved.
