Repulsive van der Waals forces due to hydrogen exposure on bilayer Graphene

TL;DR

This paper demonstrates that atomic hydrogen exposure can induce a transition from attractive to repulsive van der Waals forces between bilayer graphene, enabling tunable separation via hydrogen concentration.

Contribution

It reveals how atomic hydrogen modifies van der Waals interactions in bilayer graphene, introducing a long-range repulsive force not previously observed.

Findings

Hydrogen exposure causes van der Waals force to become repulsive at a critical concentration.

Long-range repulsion dominates at large separations due to the triple layer structure.

Doping increases attraction, reducing the net repulsive effect.

Abstract

We consider the effect of atomic hydrogen exposure to a system of two undoped sheets of graphene grown near a silica surface (the first adsorbed to the surface and the second freestanding near the surface). In the absence of atomic hydrogen the van der Waals force between the sheets is attractive at all separations causing the sheets to come closer together. However, with addition of atomic hydrogen between the sheets the long range van der Waals interaction turns repulsive at a critical concentration. The underlying triple layer structure (SiO2 -Atomic Hydrogen Gas -Air) gives rise to a long range repulsion that at large enough separations dominates over the more rapidly decaying attraction between the two-dimensional undoped graphene sheets (and between the outer graphene sheet and SiO2). This may be an avenue to tune the separation between two graphene sheets with the gas concentration. Doping of the graphene layers increases the attractive part of the interaction and hence reduces the net repulsive interaction.