Graphene adhesion on mica: Role of surface morphology

TL;DR

This study uses density functional theory to analyze how surface irregularities and potassium distribution on mica influence the adhesion and electronic properties of graphene, revealing mainly van der Waals interactions with potential doping effects.

Contribution

It provides a detailed theoretical analysis of mica-graphene adhesion considering surface morphology and charge doping, highlighting the role of surface irregularities and potassium distribution.

Findings

Adhesion is primarily van der Waals in nature.

Surface irregularities cause different binding mechanisms.

Potassium distribution affects doping and adhesion strength.

Abstract

We investigate theoretically the adhesion and electronic properties of graphene on a muscovite mica surface using the density functional theory (DFT) with van der Waals (vdW) interactions taken into account (the vdW-DF approach). We found that irregularities in the local structure of cleaved mica surface provide different mechanisms for the mica-graphene binding. By assuming electroneutrality for both surfaces, the binding is mainly of vdW nature, barely exceeding thermal energy per carbon atom at room temperature. In contrast, if potassium atoms are non uniformly distributed on mica, the different regions of the surface give rise to $n$- or $p$-type doping of graphene. In turn, an additional interaction arises between the surfaces, significantly increasing the adhesion. For each case the electronic states of graphene remain unaltered by the adhesion. It is expected, however, that the Fermi level of graphene supported on realistic mica could be shifted relative to the Dirac point due to asymmetry in the charge doping. Obtained variations of the distance between graphene and mica for different regions of the surface are found to be consistent with recent atomic force microscopy experiments. A relative flatness of mica and the absence of interlayer covalent bonding in the mica-graphene system make this pair a promising candidate for practical use.