Migration and Localization of Metal Atoms on Strained Graphene

Reconstructed point defects in graphene are created by electron irradiation and annealing. By applying electron microscopy and density functional theory, it is shown that the strain field around these defects reaches far into the unperturbed hexagonal network and that metal atoms have a high affinity to the nonperfect and strained regions of graphene. Metal atoms are attracted by reconstructed defects and bonded with energies of about 2 eV. The increased reactivity of the distorted $\pi$-electron system in strained graphene allows us to attach metal atoms and to tailor the properties of graphene.

Figure 1

Large-distance jumps of a W atom (arrowed) on a few-layer graphene sheet at $470°\mathrm{C}$ and an electron-beam current density of $110\mathrm{A}/{\mathrm{cm}}^2$. The total time [starting from (a)] is indicated. The whole path (a)–(g) is shown in (h). The dark line (top left) is the edge of a single graphene layer on the surface.

Figure 2

Oscillations of a W atom on a few-layer graphene sheet at $480°\mathrm{C}$. (a)–(d) Forth-and-back jumping between two distant trapping centers 1 and 2 (arrowed). (e)–(g) Small-scale oscillation around a trapping center. The circle is kept fixed on the lattice so that the migration of the W atom relative to the lattice is visible. The time scale is indicated.

Figure 3

(a) Atomic structure of the 555-777 defect. The bonds are colored according to an increase (blue) or decrease (red) in the bond length (given in picometers). The bonds close to pentagons are contracted, but most C-C bonds are stretched. The letters indicate all nonequivalent positions of W adatoms in the $H$ configurations. The red lines outline the ($10\times 10$) simulation cell. (b) Adsorption energy of a W adatom near the 555-777 defect as a function of separation between the adatom and the middle of the defect [circled atom in (a)]. The green triangles and red circles correspond to the bridge ($B$) and middle-of-hexagon ($H$) positions in the $10\times 10$ unit cell. Blue dots stand for the $H$ positions in the $7\times 7$ supercell. The insets show the positions of the adatoms in the lowest energy configurations. (c) Energy of a W adatom in various positions on a graphene sheet with two 555-777 defects.

Figure 4

Drop in the adsorption energy of metal adatoms adsorbed in the bridge and middle-of-hexagon positions on a nondefective graphene sheet under a biaxial strain of 1%. The energy drop is calculated with regard to the adsorption energy on unstrained graphene.