On the Dynamics of Graphdiyne Hydrogenation
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On the Dynamics of Graphdiyne Hydrogenation P. A. Autreto, J. M. de Sousa, and D. S. Galvao Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas, 13083-970, Campinas, São Paulo, Brazil. ABSTRACT Graphene is a two-dimensional (2D) hexagonal array of carbon atoms in sp2-hybridized states. Graphene presents unique and exceptional electronic, thermal and mechanical properties. However, in its pristine state graphene is a gapless semiconductor, which poses some limitations to its use in some transistor electronics. Because of this there is a renewed interest in other possible two-dimensional carbon-based structures similar to graphene. Examples of this are graphynes and graphdiynes, which are two-dimensional structures, composed of carbon atoms in sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two acetylenic groups) were recently synthesized and they can be intrinsically nonzero gap systems. These systems can be easily hydrogenated and the amount of hydrogenation can be used to tune the band gap value. In this work we have investigated, through fully atomistic molecular dynamics simulations with reactive force field (ReaxFF), the structural and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes. Our results showed that depending on whether the atoms are in the benzenoid rings or as part of the acetylenic groups, the rates of hydrogenation are quite distinct and change in time in a very complex pattern. Initially, the most probable sites to be hydrogenated are the carbon atoms forming the triple bonds, as expected. But as the amount of hydrogenation increases in time this changes and then the carbon atoms forming single bonds become the preferential sites. The formation of correlated domains observed in hydrogenated graphene is no longer observed in the case of graphdiynes. We have also carried out ab initio DFT calculations for model structures in order to test the reliability of ReaxFF calculations. INTRODUCTION The chemistry of carbon is very rich, the three different hybridization states (sp, sp2 and sp3) allow the generation of a large plethora of distinct structures, such as: graphite (sp2), diamond (sp3), fullerene (sp2), carbon nanotubes (sp2) and more recently, the hottest topic in materials science, graphene (sp2) [1]. Graphene, a two-dimensional (2D) sheet of sp2-hybridized carbon atoms exhibits extraordinary thermal, mechanical, and especially electronic properties. Because of these unique properties graphene is considered one of the most promising materials for future electronics [2]. However, in its pristine state, graphene is a gapless semiconductor, which poses some limitations to its use in transistor electronics [2]. This has renewed the interest in other possible carbon-based 2D materials, as for example, the graphyne structures [3,4]. Proposed by Baughman and co-workers in 1987 [4], graphyne is a generic name for a carbon allotrope family of 2D structures, where benzenoid rings are connected by acetylenic groups (Figure 1), with the coexist
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