Molecular adsorption in graphene with divacancy defects

We have investigated theoretically the adsorption of molecules onto graphene with divacancy defects. Using ab initio density-functional calculations, we have found that ${\text{O}}_2$, CO, ${\text{N}}_2$, ${\text{B}}_2$, and ${\text{H}}_2\text{O}$ molecules all interact strongly with a divacancy in a graphene layer. Along with a complex geometry of the molecule-graphene bonding, metallic behavior of the graphene layer in the presence of CO and ${\text{N}}_2$ molecules has been found with a large density of states in the vicinity of the Fermi level suggesting an increase in the conductivity. The adsorption of ${\text{N}}_2$ is particularly interesting since the N atoms dissociate in the vicinity of the defects and take the place where the missing C atoms of the divacancy used to sit. In this way, the defected graphene structure is healed geometrically, and at the same time doped with electron states.

Figure 1

(Color online) (a) Initial structure of ${\text{H}}_2\text{O}$, (b) final structure after geometry optimization. C, O, and H atoms are shown in yellow (light gray), red (dark gray), and turquoise (medium gray) colors, respectively.

Figure 2

(Color online) (a) Initial structure for ${\text{O}}_2$, CO, ${\text{N}}_2$, and ${\text{B}}_2$ molecules. Final relaxed structures for (b) ${\text{O}}_2$, (c) CO, (d) ${\text{N}}_2$, and (e) ${\text{B}}_2$ molecules. In all panels, C atoms are shown in yellow (light shade). In (b), O atoms are shown in red (dark gray); in (c) C and O atoms of CO are in gray (gray) and red (dark gray) respectively; in (d), N atoms are in turquoise (medium gray); and in (e) B atoms are shown in blue (blackish gray).

Figure 3

(Color online) DOS for CO on graphene. In the panels, ${\text{C}}_M$, ${\text{O}}_M$, ${\text{C}}_G$ (O) and ${\text{C}}_G$ (C) indicate DOSs for C atom in CO, O atom in CO, C atom in the graphene sheet connected to O, and C atom in the graphene sheet connected to C atom of CO molecule, respectively. For all the cases, DOSs projected on different $p$ orbitals are shown.

Figure 4

(Color online) DOSs for (top left) ${\text{H}}_2\text{O}$, (top right) ${\text{O}}_2$, (bottom left) ${\text{N}}_2$, and (bottom right) ${\text{B}}_2$ molecules are shown. In the top left panel, $\text{C-}p\left(\text{O}\right)$ and $\text{C-}p\left(\text{H}\right)$ indicate the $p$ orbitals of the C atoms of graphene bonded to O and H, respectively. For ${\text{O}}_2$, ${\text{N}}_2$, and ${\text{B}}_2$, $\text{C-}p$ indicates the $p$-orbital projected DOS for one of the C atoms connected to the molecule.