Hallmark of Perfect Graphene

Using first-principles calculations we show that the adsorption of atomic hydrogen on graphene opens a substantial gap in the electronic density of states in which lies a spin-polarized gap state. This spin is quenched by the presence of a rotated C-C bond (a Stone-Wales defect) adjacent to or distant from the H atom. We explain these findings and discuss the implications for nanotubes and magnetic nanographene. Furthermore, we demonstrate that the combined effect of high curvature and a Stone-Wales defect makes ${\mathrm{H}}_2$ chemisorption close to being thermodynamically favorable.

Figure 1

Model system in plan view (a) and side view (b) and its band structure (c) for H (light sphere) adsorbed on a 32-atom graphene sheet. In (c) the path is through the Brillouin zone of the graphene unit cell. Spin-up and spin-down channels are represented by dark and light (blue and red online) lines, respectively.

Figure 2

As in Fig. 1 but with a Stone-Wales defect. The ground state is not found to be spin polarized in this case.

Figure 3

Electronic density of states for perfect and imperfect graphene. On curve $b$ the spin-up and spin-down gap states lie at and above the Fermi level.

Figure 4

Modulated graphene sheet containing a Stone-Wales defect upon which ${\mathrm{H}}_2$ is dissociated. The sheet is modulated to produce armchairlike curvature, and the maximum curvature is equivalent to that of a (5,5) nanotube.