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Growth of large-area, few-layer graphene has been reported recently through the catalytic decomposition of methane (CH(4)) over a Cu surface at high temperature. In this study, we used ab initio calculations to investigate the minimum energy pathways of successive dehydrogenation reactions of CH(4) over the Cu (111) surface. The geometries and energies of all the reaction intermediates and transition states were identified using the climbing image nudged elastic band method. The activation barriers for CH(4) decomposition over this Cu surface are much lower than those in the gas phase; furthermore, analysis of electron density differences revealed significant degrees of charge transfer between the adsorbates and the Cu atoms along the reaction path; these features reveal the role of Cu as the catalytic material for graphene growth. All the dehydrogenation reactions are endothermic, except for carbon dimer (C(2)) formation, which is, therefore, the most critical step for subsequent graphene growth, in particular, on Cu (111) surface.

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Solvent screening is a critical aspect of the nanomorphological control of low-cost, all-solution-processed bulk heterojunction organic photovoltaic cells. In order to reveal the correlations between solvent/solvent mixtures and the bulk heterojunction nanomorphologies during solutionprocessing, we constructed a multiscale, coarse-grained molecular simulation model for ternary solvent/P3HT/ PCBM mixtures to systematically investigate the nanomorphologies of P3HT/PCBM blends during solutionprocessing in solutions over a wide range of P3HT/PCBM solubilities and solvent evaporation rates experienced during spin-casting processes. The resulting bulk heterojunction layer morphologies of the dried films were in good agreement with available experimental results from as-spun films, which validates our coarse-grained model. Our simulations indicated that the bulk heterojunction morphologies formed in solution involve a complicated interplay among the affinities of the solvent, P3HT, and PCBM in the ternary system, as well as the solubilities of the donor and acceptor; in particular, the solubility of the lessmobile material (i.e., P3HT) can notably affect the film quality, compactness, and the degree of donor/acceptor domain fineness in the dried films. Therefore, the present study demonstrates that this multiscale molecular simulation model can be used to accurately investigate the morphological evolution of bulk heterojunction blends during solution-processing and can be readily applied to the modeling of other advanced all-solution-processed organic photovoltaic cells such as small-molecule bulk heterojunction organic photovoltaic cells.