Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Calculations of Electric and Magnetic Properties of Triangular Graphene Fragments Using Density Functional Theory: Effects of Edge Functionalization and Electric Field(Izmir Institute of Technology, 2013) İyikanat, Fadıl; Senger, Ramazan TuğrulThe triangular graphene flakes (N-TGFs) we consider have equilateral triangular shapes with zigzag edges, where N denotes the number of edge hexagonal cells in one side of the triangle. Termination of these N-TGF structures with several elements (of the first two rows of the periodic table) and application of electric field to these flakes alter their electronic and magnetic properties. In accordance with previous studies [1, 2], it is found that bare flakes have large spin magnetic moment values of 4(N − 1) μB, whereas they reduce to (N − 1) μB for full saturation of edges with Hydrogen, Lithium, Beryllium or Flour atoms. Moreover we have studied possible termination of TGF with other elements like Boron, Carbon and Nitrogen. Hydrogen and Flour atoms prefer to bind at the top of an edge Carbon atom. Unlike Hydrogen and Flour, the other atoms prefer to bind at the bridge sites. Recent studies [3, 4] have shown that themagneticmoments of triangular graphene flakes can be controlled by applied electric field. We show that the value of total spin polarization of triangular graphene flakes can be changed by tuning an applied in-plane external field. We demonstrate that, in these flakes total spin polarization can be reduced stepwise with the applied field. The electric field control of ferromagnetism in TGFs promises a new route for spintronic applications.Master Thesis Electronic, Spintronic and Transport Properties of Carbon Based Nanowires(Izmir Institute of Technology, 2011) Arı, Ozan; Senger, Ramazan TuğrulIn this thesis, properties of carbon based nanowires are studied by ab-initio calculations. The aim is to gain a thorough understanding of the electronic, spintronic, transport properties in nanowires and how they are affected by different geometric formations, defects and adatom adsorptions. To this end the non-equilibrium Green's function formalism with first principles pseudopotential density functional theory calculations have been used to describe spin-polarized systems. Firstly, different geometric formations of Cobalt-Benzene nanowires are investigated. Systems with ferromagnetic ordering are calculated as half-metallic while systems with antiferromagnetic ordering behave as metallic. Also the results of the spin polarized current calculations indicate that one of the spin components of current is dominant for the antiferromagnetic systems while both spin components of current are dominant in different bias windows of a specific total applied bias. As second case, alkali atom termination of the zigzag graphene nanoribbons (ZGNR) are studied. In particular, using sodium atoms for the saturation of ZGNR edges at half the concentration of edge-carbon atoms make it a one dimensional, perfect semimetal, where the valance and conduction bands meet at only a single, Dirac-like point. Unlike pristine graphene, the Dirac-"cones" of Na-ZGNR is not symmetric with respect to wave vector, but rather it is tilted. Finally, adsorption up to the graphenic sheets with periodic 5-8 defects is studied. Especially, electronic structure of the V adsorption into 5-8 defects induced graphenic sheets are calculated as half-metallic while formation of linear bands crossing at the Fermi level which form a tilted Dirac cone.