Functionalization of graphene and stoichiometric graphene derivatives





Çıracı, Salim





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Bilkent University






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Re ent developments in experimental te hniques have made the design and produ tion of materials at nanos ale possible. In parti ular, graphene has been the fo us of resear h in diverse elds owing to high mobility arrier transport and other ex eptional properties. Over the past four years experimental studies have demonstrated that hemi al onversion of graphene to its stoi hiometri derivatives is possible by hydrogenation, uorination and hlorination. The aim of this thesis is to predi t stable stoi hiometri graphene derivatives and explore their me hani al, ele troni and magneti properties. Moreover, the fun tionalization of graphene and its derivatives are a hieved, whereby their physi al properties are modi ed to derive novel materials. Our predi tions revealing stable 2D single layer onformers, whi h an be used as novel nano oeting materials, are obtained from state-of-the art rst-prin iples Density Fun tional al ulations of total energy, phonons, transition state analysis and ab-initio mole ular dynami s. An extensive theoreti al study on the stability of hydrogenated graphene (CnH), fully hydrogenated graphane i.e graphane (CH), and their quasi onedimensional nanoribbons is performed. The formation of meshes of dehydrogenated domains on graphane resulted in geometry spe i magneti stru tures showing interesting magneti intera tions. Creation of H and CH va an ies, as well as adsorption of transition metal atoms give rise to signi ant spinpolarization in graphane nanoribbons. It is shown that as a result of one-sided or two-sided uorination of graphene one an obtain nanostru tures with diverse ele troni and magneti properties. Fully uorinated graphene or uorographene CF is a stable, sti and non-magneti semi ondu tor. Additionally, this onformer of bu kled graphene is fun tionalized by alkali, non-metal, metalloid and transition metal atoms, and ea h group leads to diverse adsorption properties. Adsorption of hlorine to graphene is dramati ally di erent from those of hydrogen and uorine. While the binding energy of hlorine is signi ant, its migration on the surfa e of perfe t graphene takes pla e almost without barrier. This is ru ial for energy harvesting on graphene surfa e. Energy optimization and phonon al ulations indi ate that the hair on guration of fully hlorinated graphene ( hlorographene) is energeti ally most favorable and stable. It is a nonmagneti semi ondu tor with 1.2 eV dire t band gap, whi h an be tuned by applied uniform strain. Graphene by itself an be fun tionalized by reating meshes of va an ies or adatoms onserving spe i symmetries. Under these ir umstan es linearly

rossing bands and hen e the massless Dira Fermion behavior an be maintained. Finally, it is demonstrated that multilayer, even single layer graphene onstitute an ex ellent nanos ale oating, whi h an prevent a rea tive metal surfa e from oxidation without hanging the size and other physi al properties. Graphene

an sti k to at metal surfa es and hinders free oxygen atom and mole ule from penetrating to the metal surfa e. Single layer uorographene an be used also for the same purposes. Design of novel nanomaterials, in parti ular biologi al mole ules and omplexes using rst-prin iples methods derived from quantum theory indi ates a new dire tion in theory, whi h promises a produ tive hybridization with experimental studies.


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