Dresden 2006 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 25: C/diamond

HL 25.4: Vortrag

Dienstag, 28. März 2006, 18:45–19:00, POT 151

Simulations of Novel Nanoporous Carbon Materials — •Johan M. Carlsson and Matthias Scheffler — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin

Carbon is one of the most versatile elements in nature and Nanoporous carbon (NPC) constitutes yet another class of carbon materials that exhibit unusual properties. NPC has the ability to catalyze dehydrogenation reactions, but the actuating chemical reaction steps are still unclear. This uncertainty is also due to the fact that the atomic structure of NPC depends on the preparation conditions. TEM experiments suggest that NPC derived from hydrocarbons has the form of crumpled graphene sheets with a significant amount of non-hexagonal rings in the structure. We have therefore carried out an extensive study to characterize NPC. Our density-functional theory (DFT) calculations reveal that the atomic relaxation transforms defects into combinations of non-hexagonal rings, which we identify as the “motifs of NPC”. These motifs lead to strain and local buckling of the structure. They also induce defect states close to the Fermi level, leading to that some of them being charged, which may facilitate molecule dissociation. These motifs can then be combined to build models of new carbon materials. A random distribution of the motifs leads to the formation of a NPC material while an ordered configuration of the motifs can instead form new, graphene like, carbon structures based on non-hexagonal rings, similar to the Haeckelites. Our calculations indicate that both NPC and the generalized Haeckelites can have a heat of formation comparable to other metastable carbon materials such as nanotubes.