Adsorption of ${\mathrm{H}}_2\mathrm{O}$, $\mathrm{N}{\mathrm{H}}_3$, CO, $\mathrm{N}{\mathrm{O}}_2$, and NO on graphene: A first-principles study

Motivated by the recent realization of graphene sensors to detect individual gas molecules, we investigate the adsorption of ${\mathrm{H}}_2\mathrm{O}$, $\mathrm{N}{\mathrm{H}}_3$, CO, $\mathrm{N}{\mathrm{O}}_2$, and NO on a graphene substrate using first-principles calculations. The optimal adsorption position and orientation of these molecules on the graphene surface is determined and the adsorption energies are calculated. Molecular doping, i.e., charge transfer between the molecules and the graphene surface, is discussed in light of the density of states and the molecular orbitals of the adsorbates. The efficiency of doping of the different molecules is determined and the influence of their magnetic moment is discussed.

Figure 1

(Color online) ${\mathrm{H}}_2\mathrm{O}$ on graphene. $4\times 4$ supercell of graphene with adsorbed ${\mathrm{H}}_2\mathrm{O}$ molecule.

Figure 2

(Color online) ${\mathrm{H}}_2\mathrm{O}$ on graphene. Inset: (a) the HOMO and (b) the LUMO of ${\mathrm{H}}_2\mathrm{O}$ (the H atoms are white and the oxygen atom is red; green and yellow indicate different signs of the orbital wave function). Main panel: DOS of ${\mathrm{H}}_2\mathrm{O}$ on graphene. The blue dotted lines show the positions of the molecular orbitals of ${\mathrm{H}}_2\mathrm{O}$.

Figure 3

(Color online) $\mathrm{N}{\mathrm{H}}_3$ on graphene. Inset: (a) the HOMO and (b) the LUMO of $\mathrm{N}{\mathrm{H}}_3$ (the N atom is blue and the H atoms are white). Main panel: DOS of $\mathrm{N}{\mathrm{H}}_3$ on graphene.

Figure 4

(Color online) CO on graphene. Inset: (a) the HOMO and (b) the LUMO of CO (the C atom is black and the O atom is red). Main panel: DOS of CO on graphene.

Figure 5

(Color online) $\mathrm{N}{\mathrm{O}}_2$ on graphene. Inset: HOMO and LUMO of $\mathrm{N}{\mathrm{O}}_2$ (the N atom is blue and the O atom is red). Main panel: spin-polarized DOS of $\mathrm{N}{\mathrm{O}}_2$ on graphene.

Figure 6

(Color online) NO on graphene. Inset: (a) $5\sigma$ orbital and (b) HOMO/LUMO of NO (the N atom is blue and the O atom is red). Main panel: spin-polarized DOS of NO on graphene.