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  • 1.
    Modarresi, Mohsen
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Ferdowsi Univ Mashhad, Iran.
    Franco Gonzalez, Felipe
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Zozoulenko, Igor
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Morphology and ion diffusion in PEDOT:Tos. A coarse grained molecular dynamics simulation2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 25, p. 17188-17198Article in journal (Refereed)
    Abstract [en]

    A Martini coarse-grained Molecular Dynamics (MD) model for the doped conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is developed. The morphology of PEDOT:Tos (i.e. PEDOT doped with molecular tosylate) and its crystallization in aqueous solution for different oxidation levels were calculated using the developed method and compared with corresponding all atomistic MD simulations. The diffusion coefficients of Na+ and Cl- ions in PEDOT:Tos are studied using the developed coarse-grained MD approach. It is shown that the diffusion coefficients decrease exponentially as the hydration level is reduced. It is also predicted that the diffusion coefficients decrease when the doping level of PEDOT is increased. The observed behavior is related to the evolution of water clusters and trapping of ions around the polymer matrix as the hydration level changes. The predicted behavior of the ionic diffusion coefficients can be tested experimentally, and we believe that molecular picture of ionic diffusion in PEDOT unraveled in the present study is instrumental for the design of polymeric materials and devices for better and enhanced performance.

  • 2.
    Mogulkoc, A.
    et al.
    Ankara University, Turkey.
    Modarresi, Mohsen
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Ferdowsi University of Mashhad, Iran.
    Rudenko, A. N.
    Radboud University of Nijmegen, Netherlands; Ural Federal University, Russia.
    Effect of long-range structural corrugations on magnetotransport properties of phosphorene in tilted magnetic field2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 8, article id 085434Article in journal (Refereed)
    Abstract [en]

    Rippling is an inherent quality of two-dimensional materials playing an important role in determining their properties. Here, we study the effect of structural corrugations on the electronic and transport properties of monolayer black phosphorus (phosphorene) in the presence of tilted magnetic field. We follow a perturbative approach to obtain analytical corrections to the spectrum of Landau levels induced by a long-wavelength corrugation potential. We show that surface corrugations have a non-negligible effect on the electronic spectrum of phosphorene in tilted magnetic field. Particularly, the Landau levels are shown to exhibit deviations from the linear field dependence. The observed effect become especially pronounced at large tilt angles and corrugation amplitudes. Magnetotransport properties are further examined in the low temperature regime taking into account impurity scattering. We calculate magnetic field dependence of the longitudinal and Hall resistivities and find that the nonlinear effects reflecting the corrugation might be observed even in moderate fields (B amp;lt; 10 T).

  • 3.
    Mogulkoc, A.
    et al.
    Ankara Univ, Turkey.
    Mogulkoc, Y.
    Ankara Univ, Turkey.
    Modarresi, Mohsen
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Ferdowsi Univ Mashhad, Iran.
    Alkan, B.
    Ankara Univ, Turkey.
    Electronic structure and optical properties of novel monolayer gallium nitride and boron phosphide heterobilayers2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 44, p. 28124-28134Article in journal (Refereed)
    Abstract [en]

    Motivated by the increasing number of studies on optoelectronic applications of van der Waals (vdW) heterostructures, we have investigated the electronic and optical properties of monolayer gallium nitride (MGaN) and boron phosphide (MBP) heterobilayers by using first-principle calculations based on density functional theory. We have ensured the dynamical stability of the structures by considering their binding energies and phonon spectra. We show that the magnitude and status (direct or indirect) of the band gap are strongly dependent on the stacking pattern of the heterobilayers. Furthermore, we have investigated the band splittings in the presence of an external electric field which show the effect of the field on the band alignment of the structure. We have also shown the band gap, charge redistributions and work function of the structures are highly dependent on the magnitude and direction of the electric field such that its magnitude yields indirect to direct band gap transitions around |E-perpendicular to| approximate to 0.7 V angstrom(-1) at the point and the order of the band gap is varied according to the direction of the electric field. Moreover, we examine optical properties of MGaN/MBP heterobilayers as part of DFT calculations. The band gap and work function being tunable with changes in the external field together with the prominent absorption over the UV range make the MGaN/MBP heterobilayer a feasible candidate for optoelectronic applications.

  • 4.
    Mogulkoc, Y.
    et al.
    Ankara University, Turkey.
    Modarresi, Mohsen
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Ferdowsi University of Mashhad, Turkey.
    Mogulkoc, A.
    Ankara University, Turkey.
    Ciftci, Y. O.
    Gazi University, Turkey.
    Alkan, B.
    Ankara University, Turkey.
    First principle and tight-binding study of strained SnC2017In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 111, p. 458-463Article in journal (Refereed)
    Abstract [en]

    We study the electronic and optical properties of strained single-layer SnC in the density functional theory (DFT) and tight-binding models. We extract the hopping parameters tight-binding Hamiltonian for monolayer SnC by considering the DFT results as a reference point. We also examine the phonon spectra in the scheme of DFT, and analyze the bonding character by using Mulliken bond population. Moreover, we show that the band gap modulation and transition from indirect to direct band gap in the compressive strained SnC. The applied tensile strain reduces the band gap and eventually the semiconductor to semimetal transition occurs for 7.5% of tensile strain. In the framework of tight-binding model, the effect of spin-orbit coupling on energy spectrum are also discussed. We indicate that while tensile strain closes the band gap, spin-orbit gap is still present which is order of similar to 40 meV at the Gamma point. The substrate effect is modeled through a staggered sub -lattice potential in the tight-binding approximation. The optical properties of pristine and strained SnC are also examined in the DFT scheme. We present the modulation of real and imaginary parts of dielectric function under applied strain.

  • 5.
    Mogulkoc, Yesim
    et al.
    Ankara Univ, Turkey.
    Modarresi, Mohsen
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Ferdowsi Univ Mashhad, Iran.
    Mogulkoc, Aybey
    Ankara Univ, Turkey.
    Alkan, Bora
    Ankara Univ, Turkey.
    Electronic and optical properties of boron phosphide/blue phosphorus heterostructures2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 17, p. 12053-12060Article in journal (Refereed)
    Abstract [en]

    The van der Waals (vdW) heterostructures are emerging as promising structures for future possible optoelectronic devices. Motivated by the recent studies on vdW heterostructures with their fascinating physical properties, we investigate the electronic and optical properties of boron phosphide/blue phosphorus heterostructures in the framework of density functional theory (DFT) and tight-binding (TB) approximations. We analyze the variation of the energy band gap, the characteristics of the energy band diagram, charge redistribution by stacking and the electrostatic potential along the perpendicular direction. The dynamical stability of these structures is ensured by the phonon spectra. We show that trilayer heterostructures of boron phosphide/bilayer blue phosphorus are in-direct band gap semiconductors while heterobilayers have a direct band gap at the K point. Moreover, we examine the optical properties of monolayer boron phosphide and heterostructures as part of DFT calculations. We conclude that the heterostructures have remarkable optical absorption over the UV range together with being transparent to the visible spectrum, and may be a prominent material for future optoelectronic devices.

  • 6.
    Nouri, N.
    et al.
    Wroclaw Univ Sci and Technol, Poland; Univ Isfahan, Iran.
    Bieniek, M.
    Wroclaw Univ Sci and Technol, Poland.
    Brzezinska, M.
    Wroclaw Univ Sci and Technol, Poland.
    Modarresi, Mohsen
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Ferdowsi Univ Mashhad, Iran.
    Borujeni, S. Zia
    Islamic Azad Univ, Iran.
    Rashedi, Gh
    Univ Isfahan, Iran.
    Wojs, A.
    Wroclaw Univ Sci and Technol, Poland.
    Potasz, R.
    Wroclaw Univ Sci and Technol, Poland.
    Topological phases in Bi/Sb planar and buckled honeycomb monolayers2018In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 382, no 40, p. 2952-2958Article in journal (Refereed)
    Abstract [en]

    We investigate topological phases in two-dimensional Bi/Sb honeycomb crystals considering planar and buckled structures, both freestanding and deposited on a substrate. We use the multi-orbital tight-binding model and compare results with density functional theory calculations. We distinguish topological phases by calculating topological invariants, analyzing edge states properties of systems in a ribbon geometry and studying their entanglement spectra. We show that coupling to the substrate induces transition to the Z(2) topological insulator phase. It is observed that topological crystalline insulator (TCI) phase, found in planar crystals, exhibits an additional pair of edge states in both energy spectrum and entanglement spectrum. Transport calculations for TCI phase suggest robust quantized conductance even in the presence of crystal symmetry-breaking disorder. (C) 2018 Elsevier B.V. All rights reserved.

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