Collaboration with E. Despiau-Pujo, LTM.
The different steps required to grow, transfer or pattern graphene samples can create defects that have been shown to alter graphene transport properties. Cleaning graphene is then a crucial issue. Recently the use of hydrogen plasma was proposed for this purpose.
The goal of the present simulations is to assist the development of graphene cleaning experiments and to understand the mechanisms of residues (CH3) removal from graphene by a hydrogen plasma. Quantum Molecular Dynamics simulation have been performed at Institut Néel. They are coupled to classical molecular dynamics simulations done by A. Davydova and E. Despiau-Pujo from LTM.
First the interaction of hydrogen with graphene has been studied. A hydrogen atom is sent with varying initial energies on top of different sites (top, hollow, bridge) of perfect graphene but also of graphene with vacancy or ribbon edges.
Then the interaction of an incident H atom with a methyl group has been simulated as a function of the incident velocity. We report the possibility for chemical etching of the methyl radical from graphene without damaging the graphene basal plane. In all cases this happens through the formation of a CH4 volatile compound that leaves graphene either in the CH4 form or breaks into a CH3 group and an isolated H atom.
|Figure 1 : QMD simulation of an H atom (incident E=2.5 eV) impiging on a CH3 radical adsorbed on graphene : a CH4 molecule is formed and desorbes from graphene.|
|Figure 2 : QMD simulation of an H atom (incident E= 8 eV) impiging on a CH3 radical adsorbed on graphene : the hydrogen atom bounces back, leaving the CH3 group adsorbed on graphene.|
E. Despiau-Pujo et al. Elementary processes of H2 plasma-graphene interaction : A combined molecular dynamics and density functional theory study. J. Appl. Phys. 113, 114302 (2013)