Sticking of Hydrogen on Supported and Suspended Graphene at Low Temperature

The physisorption of atomic hydrogen on graphene is investigated quantum mechanically using a semiempirical model for the lattice dynamics. A thermally averaged wave packet propagation describes the motion of the H atoms with respect to the membrane. Two graphene configurations, either supported on a silicone oxide substrate or suspended over a hole in the substrate, are considered. In both cases, the phonon spectrum is modified in such a way that graphene is stabilized with respect to thermal fluctuations. The sticking probabilities of hydrogen on these stabilized membranes at 10 K are high at low collision energies, and larger than on graphite.

Figure 1

Phonon dispersions for freestanding (black line), suspended (blue line), and substrate supported (red line) graphene, near the $\Gamma$ point and along the $\Gamma \mathrm{\text{−}}M$ direction in reciprocal space. The reduced wave vector is the amplitude of the wave vector, normalized to be 0.5 at the $M$ point.

Figure 2

Phonon density of states (DOS) for the 3 configurations considered in Fig. 1. The density of states are normalized such that the integral over energy is 1.

Figure 3

Sticking as a function of the kinetic energy of the incoming H atom perpendicular to the membrane. Both suspended and supported (see Fig. 1) configurations are considered.

Figure 4

Sticking populations for individual H-graphene adsorbed states, as a function of the incident H atom kinetic energy perpendicular to the membrane. Graphene is supported on a ${\mathrm{SiO}}_2$ substrate. Each state has two labels. The first is the vibrational excitation of H perpendicular to the membrane, and $g/e$ corresponds to the ground or excited diffraction state.