Hydrogen adsorption on atomic vacancies in Epitaxial graphene toward Hydrogen storage*

Defects introduction is one of the important strategy to tune graphene properties. Especially, it is known that an ion beam irradiation can introduce atomic vacancies in graphene. Although, the number of defects is usually focused, the chemical structure of defects has been not well considered. Actually, for hydrogenated atomic vacancies, the theoretical calculation shows a low energy barrier and little adsorption heat for the additional adsorption of hydrogen molecules, suggesting an efficient hydrogen storage and release in this system. In this study, hydrogenated / oxygen-terminated atomic vacancies are introduced into epitaxial graphene and the amount of hydrogen and carrier scattering related to vacancies are evaluated. Hydrogenated and oxygen-terminated atomic vacancies were introduced into epitaxial graphene by ion beam sputtering, followed by exposing to H2 gas and air, respectively. After introducing hydrogenated vacancies, the increment of hydrogen is comparable to the upper limit for the number of vacancies. The smaller Raman D-band for hydrogenated vacancies than that for oxygen terminated vacancies suggests the inter valley scattering depends on the chemical structure of defects in graphene.