Graphene: An impermeable or selectively permeable membrane for atomic species?

Graphene is generally thought to be a perfect membrane that can block completely the penetration of impurities and molecules. Here we use density-functional theory calculations to examine this property with respect to prototype atomic species. We find that hydrogen and oxygen atoms have, indeed, prohibitively large barriers (4.2 eV and 5.5 eV) for permeation through a defect-free graphene layer. We also find, however, that boron permeation occurs by an intricate bond switching synergistic process with an activation energy of only 1.3 eV, indicating easy B penetration upon moderate annealing. Nitrogen permeation has an intermediate activation energy of 3.2 eV. The results show that by controlling annealing conditions, pristine graphene could allow the selective passage of atoms.