The Dynamics of Formation of Graphane-like Fluorinated Graphene Membranes (Fluorographene): A Reactive Molecular Dynamic
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The Dynamics of Formation of Graphane-like Fluorinated Graphene Membranes (Fluorographene): A Reactive Molecular Dynamics Study Ricardo P. B. Santos1,2, Pedro A. S. Autreto1, Sergio B. Legoas3, and Douglas S. Galvao1 Instituto de Física “Gleb Wataghin, Universidade Estadual de Campinas, Campinas - SP, 13083-970, Brazil 2 Universidade Estadual de Maringá, 82020-900, Maringá - PR, Brazil. 3 Departamento de Física, CCT, Universidade Federal de Roraima, 69304-000, Boa Vista - RR, Brazil.
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ABSTRACT Using fully reactive molecular dynamics methodologies we investigated the structural and dynamical aspects of the fluorination mechanism leading to fluorographene formation from graphene membranes. Fluorination tends to produce signi¿cant defective areas on the membranes with variation on the typical carbon-carbon distances, sometimes with the presence of large holes due to carbon losses. The results obtained in our simulations are in good agreement with the broad distribution of values for the lattice parameter experimentally observed. We have also investigated mixed atmospheres composed by H and F atoms. When H is present in small quantities an expressive reduction on the rate of incorporation of fluorine was observed. On the other hand when fluorine atoms are present in small quantities in a hydrogen atmosphere, they induce an increasing on the hydrogen incorporation and the formation of locally self-organized structure of adsorbed H and F atoms. INTRODUCTION Graphene is a two dimensional array of hexagonal units of sp2 bonded C atoms [1]. Because of its electronic properties, it is considered one of the most promising materials for future electronics [2]. However, in its pristine state, it is a gapless material, which poses serious limitations to a series of electronic applications [3]. The production of graphene-like structures with well defined gap has been tried using different approaches. One possibility towards opening graphene gap is through chemical functionalization, using hydrogen or fluorine atoms [4-13]. Fully hydrogenated graphene, named graphane, was theoretically predicted by Sofo, Chaudhari, and Barber [4], and experimentally realized by Elias et al. [6]. In their experiments, graphene membranes were submitted to H+ exposure from cold plasma. The H incorporation into the membranes results in altering the carbon hybridizations from sp2 to sp3. A topological similar structure can be produced using fluorine atoms. Perfect idealized fluorographene would consist of a single-layer structure with fully saturated (sp3 hybridization) carbon atoms and with C-F bonds in an alternating pattern (up and down with relation to the plane defined by the carbon atoms) , these patterns are predicted to be found in chair, zig-zag, boat or armchair-like structures [10]. MODELING We carried out molecular dynamics (MD) simulations in order to investigate the structural and dynamical aspects of the hydrogenation and fluorination of graphene membranes, leading to the formation of graphane and flurographene-like structures.
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