engleski

Bonding of graphene on Ir(111) surface

Graphene, a two dimensional honeycomb structure of strongly bound carbon atoms, has attracted a lot of attention recently due to its electronic properties, both as a fundamental challenge and as a promising material for novel 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. The usual Density Functional Theory (DFT) calculations nicely describe the strong sp2 carbon bonds of the honeycomb structure, but either overestimate the binding of a graphene layer with the substrate (LDA) or seriously underestimate it (GGA). The reason is the lack of the proper description of the non-local corellation effects which lead to the van der Waals interaction. We have performed calculations of the structure of graphene in multilayer configurations and as an overlayer on Ir(111), by complementing the DFT calculations with the recently developed approach which takes into account the long-range correlation effects in a seamless manner. Particularly interesting is the case of Ir-graphene-Ir sandwiches, which have recently been observed experimentally in the form of a regular array of iridium clusters on top of graphene adsorbed on Ir(111) surface. Our calculations show that carbon atoms change to sp3 electronic configuration in such places, with characteristic buckling of the honeycomb lattice and lenthening of the C–C bond. We discuss the weaknesses and strengths of various DFT approaches, the standard LDA, GGA, and GGA complemented with the nonlocal correlation in a post-processing procedure. Our results give clear insight on how to treat theoretically the interaction of graphene sheets with substrates.

graphene; Ir(111) surface; DFT; long-range correlation

nije evidentirano