Cleaning graphene : a first quantum/classical molecular dynamics approach

TL;DR

This paper explores using hydrogen plasma to clean graphene by simulating how atomic hydrogen can selectively remove residues without damaging the graphene, aiming for a scalable cleaning method.

Contribution

It introduces a combined quantum and classical molecular dynamics approach to identify energy ranges for effective residue removal from graphene.

Findings

Hydrogen atoms at 2-15 eV can etch CH3 residues as CH4 without damaging graphene.

Adsorption of hydrogen on graphene occurs at these energies, enabling potential cleaning.

Further annealing is needed to restore pristine graphene after hydrogen treatment.

Abstract

Graphene outstanding properties created a huge interest in the condensed matter community and unprecedented fundings at the international scale in the hope of application developments. Recently, there have been several reports of incomplete removal of the polymer resists used to transfer as-grown graphene from one substrate to another, resulting in altered graphene transport properties. Finding a large-scale solution to clean graphene from adsorbed residues is highly desirable and one promising possibility would be to use hydrogen plasmas. In this spirit, we couple here quantum and classical molecular dynamics simulations to explore the kinetic energy ranges required by atomic hydrogen to selectively etch a simple residue, a CH3 group, without irreversibly damaging the graphene. For incident energies in the 2-15 eV range, the CH3 radical can be etched by forming a volatile CH4 compound which leaves the surface, either in the CH4 form or breaking into CH3+H fragments, without further defect formation. At this energy, adsorption of H atoms on graphene is possible and further annealing will be required to recover pristine graphene.