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Illustration of defects: (a) open “edge” vacancy structure at position 1, (b) the elevated Fe/vacancy complex at position 5, (c) cyclononane/cyclopentane relaxed vacancy at position 6, (d) pyridinic vacancy structure at position 4, (e) Fe/pyridinic vacancy at position 7, and (f) pyridinic vacancy structure at position 2 (near-edge). All structures are shown illustrated for the n = 7 GNR. Positions are assigned based on carbon vacancy distance from edge as shown by the numbering system in the upper right hand corner.
Vacancy and pyridinic vacancy formation energy as a function of position. The offset indicates that the presence of nitrogen stabilizes the formation of vacancies in graphene by several eV.
Fe/vacancy formation energy and binding energy as a function of position. Pre-existing vacancies bind Fe most strongly at the center of the GNR, whereas Fe lowers the vacancy formation energy most strongly at the edge.
Pyridinic vacancies in position 5(a) and position 4(b). Arrows represent strain with odd parity vacancies having outward strain and even parity vacancies having inward strain. This strain, superposed on the general trend of increased formation energies at the GNR center, produces the non-monotonic behavior of pyridinic vacancy formation energy.
Fe/pyridinic vacancy formation energy and binding energy as a function of position. The non-monotonic behavior is related to the relaxation of Fe and N atoms out of the plane of the surrounding GNR structure.
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