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OO5.02 - Formation Conditions for Epitaxial Graphene on Diamond (111) Surfaces 
April 22, 2014   11:00am - 11:15am

The phase transformation from a non-terminated diamond (111) surface to graphene, has in the present study been simulated using ab initio Molecular Dynamic calculations at different temperatures and under various reaction conditions. For vacuum conditions, the graphitization process was found to start at about 800 K, with a final graphene-like adlayer obtained at 2500 K. The C-C bonds across the interface were found to be broken gradually when increasing the temperature. The resulting graphene-like adlayer at 2500 K was observed to chemisorb to the underlying diamond surface with 33% of the initial C-C bonds, and with a C-C covalent energy value of 3.4 eV. The corresponding density of states spectra show a p-doped character, as compared with graphene. When introducing H radicals during the annealing process, a graphene-like adlayer started to be formed at a much lower temperature; 500K. The completeness of the diamond-to-graphene process was found to depend on the concentration of H radicals in the lattice. When the number of H radicals reached 34 within a super cell, a final free-standing graphene monolayer was formed at 1000 K. When introducing a larger concentration of H radicals into the lattice in the initial part of the annealing process, the formation of a free-standing graphene layer was found at an even lower H concentration and lower temperature (17 H within the supercell, and at 1000 K).

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