Graphene on Ir(111) surface: From van der Waals to strong bonding

TL;DR

This study uses advanced density functional theory methods to analyze the bonding nature of graphene on Ir(111), revealing a transition from van der Waals to strong covalent bonds upon metal atom adsorption.

Contribution

It introduces the application of vdW-DF functional to model graphene-metal interactions, capturing both weak and strong bonding regimes.

Findings

Van der Waals forces dominate initial graphene adsorption on Ir(111).

Additional iridium atoms induce covalent bonding with graphene.

The model effectively describes the transition from weak to strong bonding.

Abstract

We calculate the properties of a graphene monolayer on the Ir(111) surface, using the model in which the periodicities of the two structures are assumed equal, instead of the observed slight mismatch which leads to a large superperiodic unit cell. We use the Density Functional Theory approach supplemented by the recently developed vdW-DF nonlocal correlation functional. The latter is essential for treating the van der Waals interaction, which is crucial for the adsorption distances and energies of the rather weakly bound graphene. When additional iridium atoms are put on top of graphene, the electronic structure of C atoms acquires the sp3 character and strong bonds with the iridium atoms are formed. We discuss the validity of the approximations used, and the relevance for other graphene-metal systems.