Cleaning Graphene: what can be learned from Quantum/Classical Molecular Dynamics
Simulations
L.Magaud , L.Delfour1, A.Davydova2, E.Despiau-Pujo2, G.Cunge2
1
Institut Néel, CNRS and Grenoble-Alpes, Grenoble, France
LTM, CNRS/UJF-Grenoble1, CEA Grenoble, France
Laurence.magaud@neel.cnrs.fr
Graphene tremendous electronic properties [1] are closely linked to its pristine honeycomb lattice.
During the synthesis or the successive steps needed to create devices, hydrocarbon radicals often
adsorb on graphene samples [2]. These radicals are known to alter the transport properties [3].
Cleaning graphene is then of primary importance but it remains a difficult task. One promising route for
this is the use of a hydrogen plasma. As a first step to model graphene cleaning, we have investigated
the etching, by atomic hydrogen, of a CH3 radical adsorbed on graphene [4] (Figure 1). As a function of
the incident energy, Quantum Molecular Dynamics shows either formation and desorption of a CH 4
molecule (Figure 2), etching as a CH3 radical (Figure 3) or no change in the configuration. The effect of
an incident H atom on a free graphene layer will also be detailed for comparison. We will show that the
energy range that enables the CH3 radical etching also leads to the adsorption of H atoms on graphene.
Links to experimental results will be given.
Quantum Molecular dynamics results are obtained in the NVE ensemble using the code VASP and
PAW potentials [6]. Classical MD calculations based on the well tested C-H REBO [7,5] potential have
also been performed to enable longer dynamics and to test the effect of graphene temperature.
References
[1] K. S. Novoselov et al., Nature 490 (2012), 192
[2] A.Pirkle et al,, J. Appl. Phys. Lett. 99 (2011) 122108.
[3] Y.Ahn, H.Kim, Y.-H.Kim, Y.Yi, S.-I.Kim. Appl. Phys. Lett. 102 (2013), 091602.
[4] L.Delfour, A.Davydova, E.Despiau-Pujo, G.Cunge, D.B.Graves, L.Magaud, submitted to Phys. Rev B
[5] E.Despiau-Pujo, A.Davydova, G.Cunge, L.Delfour, L.Magaud, D.B.Graves. J. Appl. Phys. . 2013,
113, 114302.
[6] G.Kresse and J.Hafner, Phys. Rev. B 47 (1993), 558
[7] D. W. Brenner, O. A. Shenderova, J. A. Harrison et al., J. Phys.: Condens.
Matter 14 (2002), 783 .
Figures
Figure 1: Top view of a CH3 radical absorbed on a graphene surface.
a)
b)
c)
Figure 2: Isocharge contours for a H atom arriving on a CH3 radical adsorbed on graphene with an
incident energy equal to 1 eV. a) initial configuration, b) formation of CH 4, c) etching of CH4.
Figure 3: Etching of a CH3 radical by an H atom with an incident energy equal to 4 eV. Snapshots for
different simulation times, from left to right and top to bottom: 0 fs, 17 fs, 33 fs, 47 fs, 68 fs.