Manipulating absorption and diffusion of H atom on graphene by mechanical strain

Effects of the tensile strain on absorption and diffusion of hydrogen atoms on graphene have been studied by first-principles calculations. Our calculations suggested that there exists a barrier of 0.22 eV for H atom to diffuse from free space to graphene. The barrier originates from the transition of the hybridization of the H-binded carbon atom in graphene from sp2 to sp3, and is robust against the tensile strain. It was also found that, first, the in-plane diffusion of H atoms on graphene is unlikely to happen at low temperature due to the high barrier without or with strain, and second, the tensile strain along the armchair direction greatly decreases the out-plane diffusion barrier of H atoms, making it possible at low temperature. In particular, when the armchair strain is moderate (<10%), we found that the out-plane diffusion of H atoms likely to happen by diffusing through C-C bonds, and for relatively large armchair strain around 15%, the out-plane diffusion will happen though the center of the benzene ring.