Control of graphene's properties by reversible hydrogenation

TL;DR

This paper demonstrates reversible hydrogenation of graphene, transforming it from a conductor to an insulator and back, enabling the design of new two-dimensional materials with tailored electronic properties.

Contribution

It provides experimental evidence that hydrogenation can reversibly modify graphene's electronic structure and lattice, introducing a new method for creating customizable 2D materials.

Findings

Hydrogenation turns graphene into an insulator while retaining its lattice structure.

The process is reversible, restoring graphene's original metallic state.

Hydrogenated graphene shows a shorter lattice period and recoverable quantum Hall effect.

Abstract

Graphene - a monolayer of carbon atoms densely packed into a hexagonal lattice - has one of the strongest possible atomic bonds and can be viewed as a robust atomic-scale scaffold, to which other chemical species can be attached without destroying it. This notion of graphene as a giant flat molecule that can be altered chemically is supported by the observation of so-called graphene oxide, that is graphene densely covered with hydroxyl and other groups. Unfortunately, graphene oxide is strongly disordered, poorly conductive and difficult to reduce to the original state. Nevertheless, one can imagine atoms or molecules being attached to the atomic scaffold in a strictly periodic manner, which should result in a different electronic structure and, essentially, a different crystalline material. A hypothetical example for this is graphane, a wide-gap semiconductor, in which hydrogen is bonded to each carbon site of graphene. Here we show that by exposing graphene to atomic hydrogen, it is possible to transform this highly-conductive semimetal into an insulator. Transmission electron microscopy reveals that the material retains the hexagonal lattice but its period becomes markedly shorter than that of graphene, providing direct evidence for a new graphene-based derivative. The reaction with hydrogen is found to be reversible so that the original metallic state and lattice spacing are restored by annealing and even the quantum Hall effect recovers. Our work proves the concept of chemical modification of graphene, which promises a whole range of new two-dimensional crystals with designed electronic and other properties.