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    Adsorption of alkali and alkaline-earth metal atoms on stanene: A first-principles study
    (Elsevier Science Sa, 2016) Kadioglu, Yelda; Ersan, Fatih; Gokoglu, Gokhan; Akturk, Olcay Uzengi; Akturk, Ethem
    This paper presents a study on the adsorption of alkali and alkaline-earth metal atoms on single-layer stanene with different levels of coverage using first-principles plane wave calculations within spin polarized density functional theory. The most favorable adsorption site for alkali atoms (Li, Na, K) were found to be the hollow site similar to other group IV single-layers, but the case of alkaline-earths on stanene is different from silicene and germanene. Whereas Mg and Ca are bound to stanene at hollow site, the bridge site is found to be energetically favorable for Be adatom. All adsorbed atoms are positively charged due to the charge transfer from adatom to stanene single-layer. The semimetallic bare stanene become metallic except for Be adsorption. The Beryllium adsorption give rise to non-magnetic semi-conducting ground state. Our results illustrate that stanene has a reactive and functionalizable surface similar to graphene or silicene. (C) 2016 Elsevier B.V. All rights reserved.
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    Effects of gold based dimers on structural and electronic properties of MoS2
    (Elsevier, 2017) Kadioglu, Yelda; Gokoglu, Gokhan; Akturk, Olcay Uzengi
    In view of first principles calculations, we investigate the electronic structure redecoration of monolayer MoS2 upon adsorptions of AuAg, AuPt, AuPd, AuCu, and AuAl bimetallic dimers. Geometrical structure, band structures, electronic density of states, charge density differences of dimer adsorbed MoS2 systems are presented and discussed. All the systems studied have non-magnetic ground states. Charge transfers occur from dimer to surface except for AuPt adsorption. Our results indicate that the semiconductor MoS2 maintains its semiconductor character with decreased band gaps upon AuAg, AuCu, and AuAl adsorptions. However, MoS2 shows metallic behaviour by AuPt and AuPd adsorptions, so Pt-d and Pd-d states cross Fermi level yielding metallic character. AuPt adsorbed system has the highest Eads value of 3.15 eV indicating the most stable structure energetically among the dimer adsorbed MoS2 systems considered. (C) 2016 Elsevier B.V. All rights reserved.
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    Molecular adsorption properties of CO and H2O on Au-, Cu-, and AuxCuy-doped MoS2 monolayer
    (Elsevier, 2017) Kadioglu, Yelda; Gokoglu, Gokhan; Akturk, Olcay Uzengi
    In this study, we investigate the adsorption properties of Au, Cu, and AuxCuy nanoclusters on MoS2 sheet and the interactions of the adsorbed systems with CO and H2O molecules by using first principles calculations. Results indicate that Au, Cu, or AuxCuy strongly binds to MoS2 monolayer resulting in enhanced chemical activity and sensitivity toward CO and H2O molecules compared to bare MoS2 monolayer. Although both CO and H2O molecules bind weakly to pristine MoS2 monolayer, CO strongly binds to MoS2 sheet in the presence of Au, Cu atoms or AuxCuy clusters. Semiconductor MoS2 monolayer turns into metal upon Au or Cu adsorption. AuxCuy nanocluster adsorption decreases the band gap of MoS2 monolayer acting as a n-type dopant. AuxCuy-doped MoS2 systems have improved adsorption properties for CO and H2O molecules, so the conclusions provided in this study can be useful as a guide for next generation device modeling. (C) 2017 Elsevier B.V. All rights reserved.
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    T-ZrS2 nanoribbons: structure and electronic properties
    (Taylor & Francis Ltd, 2016) Ersan, Fatih; Kadioglu, Yelda; Gokoglu, Gokhan; Akturk, Olcay Uzengi; Akturk, Ethem
    Recently, monolayer and few layers of trigonal phases of zirconium disulfide ( T-ZrS2) sheets were obtained experimentally on hexagonal boron nitride using an evaporation technique. On the basis of these previous results, we report the structural and electronic properties of armchair nanoribbons ( ANRs) and zigzag nanoribbons ( ZNRs) of T-ZrS2 by means of density functional theory. According to our results, both ANRs and ZNRs are nonmagnetic semiconductors similar to a two-dimensional T-ZrS2 monolayer. The semiconducting character is not altered by termination of the edge atoms with hydrogen. The band gaps are associated with the ribbon widths and edge structures. The band gaps of bare and H-terminated ANR-ZrS2 decrease exponentially, whereas the band gaps of ultra-narrow zigzag nanoribbons oscillate slightly with increasing ribbon width. Although the band gaps of bare ANRs approach that of 2D T-ZrS2, other structures have larger band gaps than the monolayer with increasing ribbon width. The cohesive and formation energies of bare ANRs and ZNRs converge rapidly to that of the 2D T-ZrS2 structure with increasing ribbon width.
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    Tuning the electronic structure of RhX3 (X = Cl, Br, I) nonmagnetic monolayers: effects of charge-injection and external strain
    (Royal Soc Chemistry, 2020) Kadioglu, Yelda; Ozdemir, Ilkay; Akturk, Olcay Uzengi; Gokoglu, Gokhan; Akinci, Umit; Akturk, Ethem
    Atomistic exploration and electronic modification of 2D materials have been a central focus of research since the breakthrough of graphene. In the present study, we introduce and reveal the structure, stability and electronic features of novel RhX3 (X: Cl, Br, I) monolayer systems within the framework of density functional theory. Phonon dispersion spectra and equilibrium molecular dynamics calculations confirm the stability of the phases studied at room and elevated temperatures. The structures are slightly modified because of thermal excitations and maintain their stabilities up to 1000 K. We show that the electronic and magnetic nature of pristine monolayers can be tuned by external effects, i.e. both mechanically and electrically. RhCl3, RhBr3 and RhI3 monolayers are nonmagnetic and indirect-gap semiconductors intrinsically, but display indirect-to-direct band gap transitions at particular strain values. The systems gain a net magnetic moment and are transformed into metals by negative charging. The optical properties, such as the absorption coefficient, optical conductivity, energy loss spectrum, refractive index and extinction coefficient, are also presented. This interesting class of nanomaterials are promising candidates for several applications in nanotechnology and optoelectronics with good thermal stability, mechanical flexibility, and tunable electronic properties.