Lattice strain effects in graphane and partially-hydrogenated graphene sheets
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1216-W03-10
Lattice strain effects in graphane and partially-hydrogenated graphene sheets James R. Morris,1,2 Frank W. Averill,1,2 Haiyan He,3 Bicai Pan,3 Valentino R. Cooper,1 Lujian Peng2 1
Materials Sciences & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831-6115, USA. 2
Department of Material Science and Engineering, University of Tennessee, Knoxville, TN, 37996-2200, USA. 3
Department of Physics, University of Science and Technology of China, Hefei, CHINA
ABSTRACT This paper presents a brief review of recent developments in the studies of fully hydrogenated graphene sheets, also known as “graphane,” and related initial results on partially hydrogenated structures. For the fully hydrogenated case, some important discrepancies, specifically whether or not the graphene sheet expands or contracts upon hydrogenation, exist between published first-principles calculations, and between calculations and experiment. The lattice change has important effects on partially hydrogenated structures. In addition, calculations of the interfacial energy must carefully account for the strain energy in neighboring regions: For sufficiently large regions between interfaces, defects at the interface which relieve the strain may be energetically preferable. Our preliminary first-principles calculations of ribbon structures, with interfaces between graphane and graphene regions, indicate that the interfaces do indeed have substantial misfit strains. Similarly, our tight-binding simulations show that at ambient temperatures, segments of graphene sheets may spontaneously combine with atomic hydrogen to form regions of graphane. Here, small amounts of chemisorbed hydrogen distort the graphene layer, due to the lattice misfit strain, and may induce the adsorption of more hydrogen atoms. INTRODUCTION The capability of isolating single graphene layers has increased interest in the properties of such layers. While much of the interest is in the electronic structure of isolated, finite-sized regions of a graphene sheet, there has also been interest in chemically modified graphene, particularly in both fully [1-3] and partially [4] hydrogenated forms. This has also been recently extended to structurally similar materials, including boron nitride sheets and BC2N sheets [3]. Recent experiments [5] provide evidence that graphene, when exposed with atomic hydrogen, may reversibly react; returning to pure graphene upon annealing. Of interest is the question of whether the graphene plane expands or contracts when reacting with hydrogen. This has a particularly important role in the interface between graphene and graphane, where there is a misfit strain. Such a misfit strain may have an effect on the nucleation of graphane regions and on the coherency of the interface when the graphene and graphane regions are large. Previously, our first-principles calculations suggested that
hydrogenation would result in an expansion of the graphane lattice relative to pure graphene [3] . Here, based on preliminary first-principles cal
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