engleski

Bonding of graphene in multilayers and overlayers

Graphene, a two dimensional honeycomb structure of strongly bound carbon atoms, has attracted a lot of attention recently due to its electronic properties. The "Dirac fermions" with linear dispersion around the Fermi level constitute a theoretical challenge from the fundamental point of view, while also opening the possibility for novel kinds of electronic devices. Graphene is the building block of graphite, which has been used to exfoliate single or multiple layers onto insulating substrates. Graphene layers have also been prepared on SiC and metals by various growth techniques. Unlike very strong in-plane bonds, the interaction in the direction perpendicular to the graphene plane are much weaker and demands specialized theoretical approaches. The usual Density Functional Theory (DFT) calculations nicely describe the honeycomb structure, but either overestimate the interlayer binding (LDA) or seriously underestimate it (GGA). We have performed calculations of the structure and electronic properties of graphene in multilayer configurations and as overlayers on metals, by complementing the DFT calculations with long range correlation effects, which is necessary to include the van der Waals interaction, using several approaches. We have used an asymptotic approach which is useful when the system consists of weakly bound "fragments", and a recently developed therory which replaces the semilocal correlation of the DFT GGA by a fully nonlocal quantity in a "seamless" fashion. We obtained good result for both graphene multilayer (i.e. graphite) and graphene on metals, in particular iridium. We also considered Ir-graphene-Ir stacks, and found that under certain conditions the C-Ir interaction switches over to a strong organometallic bond with much shorter equilibrium distance, which has been recently observed at certain positions of the moiré structure of graphene on Ir(111) surface. Our results give clear insight on how to treat theoretically the interaction of graphene sheets with a variety of substrates.

graphene; iridium; density functional theory; long range correlation

nije evidentirano