Gate-Voltage Control of Oxygen Diffusion on Graphene

We analyze the diffusion of oxygen atoms on graphene and its dependence on the carrier density controlled by a gate voltage. We use density functional theory to determine the equilibrium adsorption sites, the transition state, and the attempt frequency for different carrier densities. The ease of diffusion is strongly dependent on carrier density. For neutral graphene, we calculate a barrier of 0.73 eV; however, upon electron doping the barrier decreases almost linearly to reach values as low as 0.15 eV for densities of $-7.6\times {10}^{13}{\mathrm{cm}}^{-2}$. This implies an increase of more than 9 orders of magnitude in the diffusion coefficient at room temperature. This dramatic change is due to a combined effect of bonding reduction in the equilibrium state and bonding increase at the transition state and can be used to control the patterning of oxidized regions by an adequate variation of the gate voltage.

Figure 1

Equilibrium (left) and transition (right) state geometry for one oxygen atom (red) adsorbed on graphene (light gray). The measurements indicated by the labels are reported in Table . $P$ represents puckering with respect to the graphene plane.

Figure 2

Energies of the different configurations used to determine the transition state. The first and the last configuration correspond to the equilibrium state ($E$) and the central configuration is the transition state ($T$). The distance is the same between all images and does not represent the real distance between oxygen positions.

Figure 3

Total density of states (DOS) and the partial densities of states corresponding to the O $p_z$ orbital and the $p$ orbitals parallel to the plane as a function of energy measured from the Fermi level. The left-hand panels correspond to the equilibrium state for the neutral plane (a) and the electron-doped plane with density $-7.64\times {10}^{13}{\mathrm{cm}}^{-2}$ (c). The right-hand panels correspond to the transition state neutral (b) and electron-doped with density $-7.64\times {10}^{13}{\mathrm{cm}}^{-2}$ (d). O projections are rescaled for clarity.