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Search Results: 1 - 10 of 3649 matches for " Hasan Sahin "
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Graphene Nanomeshes: Existence of Defect-Induced Dirac Fermions on Graphene Host Matrix
Hasan Sahin,Salim Ciraci
Physics , 2011,
Abstract: Motivated by the state of the art method for fabricating high density periodic nanoscale defects in graphene, the structural, mechanical and electronic properties of defect-patterned graphene nanomeshes including diverse morphologies of adatoms and holes are investigated by means of first-principles calculations within density functional theory. It is found that various patterns of adatom groups yield metallic or semimetallic, even semiconducting behavior and specific patterns can be in a magnetic state. Even though the patterns of single adatoms dramatically alter the electronic structure of graphene, adatom groups of specific symmetry can maintain the Dirac fermion behavior. Nanoholes forming nanomesh are also investigated. Depending on the interplay between the repeat periodicity and the geometry of the hole, the nanomesh can be in different states ranging from metallic to semiconducting including semimetallic state with the bands crossing linearly at the Fermi level. We showed that forming periodically repeating superstructures in graphene matrix can develop a promising technique to engineer nanomaterials with desired electronic and magnetic properties.
Chlorine Adsorption on Graphene: Chlorographene
Hasan Sahin,Salim Ciraci
Physics , 2012, DOI: 10.1021/jp307006c
Abstract: We perform first-principles structure optimization, phonon frequency and finite temperature molecular dynamics calculations based on density functional theory to study the interaction of chlorine atoms with graphene predicting the existence of possible chlorinated graphene derivatives. The bonding of a single chlorine atom is ionic through the transfer of charge from graphene to chlorine adatom and induces negligible local distortion in the underlying planar graphene. Different from hydrogen and fluorine adatoms, the migration of a single chlorine adatom on the surface of perfect graphene takes place almost without barrier. However, the decoration of one surface of graphene with Cl adatoms leading to various conformations cannot sustain due to strong Cl-Cl interaction resulting in the desorption through the formation of Cl$_2$ molecules. On the contrary, the fully chlorinated graphene, chlorographene CCl, where single chlorine atoms are bonded alternatingly to each carbon atom from different sides of graphene with $sp^3$-type covalent bonds, is buckled. We found that this structure is stable and is a direct band gap semiconductor, whose band gap can be tuned by applied uniform strain. Calculated phonon dispersion relation and four Raman-active modes of chlorographene are discussed.
First Principles Calculations of Spin-Dependent Conductance of Graphene Flakes
Hasan Sahin,Ramazan Tugrul Senger
Physics , 2008, DOI: 10.1103/PhysRevB.78.205423
Abstract: Using ab initio density functional theory and quantum transport calculations based on nonequilibrium Green's function formalism we study structural, electronic, and transport properties of hydrogen-terminated short graphene nanoribbons (graphene flakes) and their functionalization with vanadium atoms. Rectangular graphene flakes are stable, having geometric and electronic structures quite similar to that of extended graphene nanoribbons. We show that a spin-polarized current can be produced by pure, hydrogenated rectangular graphene flakes by exploiting the spatially-separated edge states of the flake using asymmetric, non-magnetic contacts. Functionalization of the graphene flake with magnetic adatoms such as vanadium also leads to spin-polarized currents even with symmetric contacts. We observe and discuss sharp discontinuities in the transmission spectra which arise from Fano resonances of localized states in the flake.
Adsorption of Alkali, Alkaline Earth and Transition Metal Atoms on Silicene
Hasan Sahin,Francois M. Peeters
Physics , 2013, DOI: 10.1103/PhysRevB.87.085423
Abstract: The adsorption characteristics of alkali, alkaline earth and transition metal adatoms on silicene, a graphene-like monolayer structure of silicon, are analyzed by means of first-principles calculations. In contrast to graphene, interaction between the metal atoms and the silicene surface is quite strong due to its highly reactive buckled hexagonal structure. In addition to structural properties, we also calculate the electronic band dispersion, net magnetic moment, charge transfer, workfunction and dipole moment of the metal adsorbed silicene sheets. Alkali metals, Li, Na and K, adsorb to hollow site without any lattice distortion. As a consequence of the significant charge transfer from alkalis to silicene metalization of silicene takes place. Trends directly related to atomic size, adsorption height, workfunction and dipole moment of the silicene/alkali adatom system are also revealed. We found that the adsorption of alkaline earth metals on silicene are entirely different from their adsorption on graphene. The adsorption of Be, Mg and Ca turns silicene into a narrow gap semiconductor. Adsorption characteristics of eight transition metals Ti, V, Cr, Mn, Fe, Co, Mo and W are also investigated. As a result of their partially occupied d orbital, transition metals show diverse structural, electronic and magnetic properties. Upon the adsorption of transition metals, depending on the adatom type and atomic radius, the system can exhibit metal, half-metal and semiconducting behavior. For all metal adsorbates the direction of the charge transfer is from adsorbate to silicene, because of its high surface reactivity. Our results indicate that the reactive crystal structure of silicene provides a rich playground for functionalization at nanoscale.
Magnetization of Graphane by Dehydrogenation
Hasan Sahin,Can Ataca,Salim Ciraci
Physics , 2009, DOI: 10.1063/1.3268792
Abstract: Each single hydrogen vacancy created at the surface of graphane gives rise to a local unpaired spin. For domains of hydrogen vacancies the situation is, however complex and depends on the size and geometry of domains, as well as whether the domains are single- or double-sided. In single-sided domains, hydrogen atoms at the other side are relocated to pair the spins of adjacent carbon atoms by forming pi-bonds. Owing to the different characters of exchange coupling in different ranges and interplay between unpaired spin and the binding geometry of hydrogen, vacancy domains can attain sizable net magnetic moments. Our results based on the first-principles calculations suggest that the size and ordering of magnetic moments of hydrogen vacancy domains with thin walls can be used for future data storage and spintronics applications.
Graphane Nanoribbons: A Theoretical Study
Hasan Sahin,Can Ataca,Salim Ciraci
Physics , 2010, DOI: 10.1103/PhysRevB.81.205417
Abstract: In this study, we investigate the electronic and magnetic properties of graphane nanoribbons. We find that zigzag and armchair graphane nanoribbons with H-passivated edges are nonmagnetic semiconductors. While bare armchair ribbons are also nonmagnetic, adjacent dangling bonds of bare zigzag ribbons have antiferromagnetic ordering at the same edge. Band gaps of the H-passivated zigzag and armchair nanoribbons exponentially depend on their width. Detailed analysis of adsorption of C, O, Si, Pt, Ti, V and Fe atoms on the graphane ribbon surface reveal that functionalization of graphane ribbons is possible via these adatoms. It is found that C, O, V and Pt atoms have tendency to replace H atoms of graphane. We showed that significant spin polarizations in graphane can be achieved through creation of domains of H-vacancies and CH-divacancies.
Structures of Fluorinated Graphenes and Their Signatures
Hasan Sahin,Mehmet Topsakal,Salim Ciraci
Physics , 2011, DOI: 10.1103/PhysRevB.83.115432
Abstract: Recent synthesis of fluorinated graphene introduced interesting stable derivatives of graphene. In particular, fluorographene (CF), namely fully fluorinated chair conformation, is found to display crucial features, such as high mechanical strength, charged surfaces, local magnetic moments due to vacancy defects and a wide band gap rapidly reducing with uniform strain. These properties, as well as structural parameters and electronic densities of states are found to scale with fluorine coverage. However, most of the experimental data reported to date neither for CF, nor for other CnF structures complies with the results obtained from first-principles calculations. In this study, we attempt to clarify the sources of disagreements.
Spintronic Properties of Zigzag-Edged Triangular Graphene Flakes
Hasan Sahin,R. Tugrul Senger,Salim Ciraci
Physics , 2010, DOI: 10.1063/1.3489919
Abstract: We investigate quantum transport properties of triangular graphene flakes with zigzag edges by using first principles calculations. Triangular graphene flakes have large magnetic moments which vary with the number of hydrogen atoms terminating its edge atoms and scale with its size. Electronic transmission and current-voltage characteristics of these flakes, when contacted with metallic electrodes, reveal spin valve and remarkable rectification features. The transition from ferromagnetic to antiferromagnetic state under bias voltage can, however, terminate the spin polarizing effects for specific flakes. Geometry and size dependent transport properties of graphene flakes may be crucial for spintronic nanodevice applications.
The Use of Seed Proteins Revealed by SDS-PAGE in Taxonomy of Some Lathyrus L. Species Grown in Turkey
Irfan Emre,Dilek Turgut-Balik,Hasan GENC,Ahmet Sahin
Pakistan Journal of Biological Sciences , 2006,
Abstract: In this study total 9 taxa belong to four different sections (Pratensis, Orobon, Orobus and Platystylis) collected from different regions of Turkey have been studied for the analysis of seed storage protein profiles to examine their relationship by sodium dodecyl sulphate polyacrilamide gel electrophoresis (SDS-PAGE) technique. Data obtained from electrophoresis of seed proteins were analysed using hierarchical clustering analysis and Euclidean distance was used for calculating the genetic resemblance. Dendogram was formed using average linkage. Electrophoretic protein profiles of seed cotyledons were showed that all taxa except for L. brachypterus var. brachypterus formed two clusters. The first one consisted of L. pratensis, L. laxiflorus subsp. laxiflorus, L. roseus and the second one L. digitatus, L. spathulatus, L. boissieri L. nivalis and L. aureus. In addition, total protein profile differences were observed when four taxa originated from 9 geographical regions belong to three sections (Sections Platystylis, Pratensis and Orobon) were analysed. Protein amount was found to be highest in L. spathulatus and lowest in L. brachypterus var. brachypterus.
The Versatile Use of Temporoparietal Fascial Flap
Cenk Demirdover, Baris Sahin, Haluk Vayvada, Hasan Yucel Oztan
International Journal of Medical Sciences , 2011,
Abstract: Background: The pedicled or free temporoparietal fascial has been used in many areas, especially in head and neck reconstruction. This thin, pliable, highly vascularized flap may be also transferred as a carrier of subjacent bone or overlying skin. Objective: The aim of this study is to report our experience in versatile use of temporoparietal fascial flap (TPFF) and discuss the surgical anatomy and technique. Patients and Methods: A total number of 57 TPFFs have been used in periorbital, mid-facial, auricular, and tracheal reconstruction due to tumor resection, trauma, and congenital ear deformities. Results: All the flaps were successfully transferred without any major complication. The cosmetic results were quite satisfactory to all patients. Conclusion: The advantages and minimal donor site morbidity of TPPF makes this flap a good choice in many reconstructive procedures.
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