Metals on graphene: correlation between adatom adsorption behavior and growth morphology

Abstract

We present a systematic study of metal adatom adsorption on graphene by ab initio calculations. The calculations cover alkali metals, sp-simple metals, 3d and group 10 transition metals, noble metals, as well as rare earth metals. The correlation between the adatom adsorption properties and the growth morphology of the metals on graphene is also investigated. We show that the growth morphology is related to the ratio of the metal adsorption energy to its bulk cohesive energy (E(a)/E(c)) and the diffusion barrier (ΔE) of the metal adatom on graphene. Charge transfer, electric dipole and magnetic moments, and graphene lattice distortion induced by metal adsorption would also affect the growth morphologies of the metal islands. We also show that most of the metal nanostructures on graphene would be thermally stable against coarsening.

Atomistic modeling of the directed-assembly of bimetallic Pt-Ru nanoclusters on Ru(0001)-supported monolayer graphene

“…The adsorption energy of a Pt (Ru) adatom on freestanding MLG has the value ∼ −1.6 eV (−2.0 eV) and the diffusion barrier has the value ∼0.17 eV (0.62 eV). 26,31 Thus, the interaction of Pt with graphene is somewhat weaker than that of Ru. There also exist DFT results for the adsorption energy (E ads ) in preferred fcc region for these metals on supported MLG/Ru(0001): ∼ −2.8 eV for Pt versus −2.6 eV for Ru.…”

Direct capture and electrostatic repulsion in the self-assembly of rare-earth atom superlattices on graphene

“…Note that transition metals preferentially adsorb on hcp regions [27], indicating a different adsorption mechanism than for rare earths. Calculations show that rare earths on freestanding graphene present similarities with alkali metals, with a bond that is mainly ionic and the charge transferred from the atom to the graphene delocalized over several graphene cells [31]. For Cs on gr/Ir(111), density functional theory (DFT) calculations found that adsorption is favored in the vicinity of the atop region of the moiré cell [25].…”

“…Only for higher temperatures, dimers form by lateral attachment of adatoms diffusing toward each other from far distances. This is indicative of a repulsion between the atoms that can only be overcome for T > 50 K. This repulsion is very likely electrostatic, since rare-earth atoms, similar to alkali atoms [24,31], are expected to transfer electrons to graphene [25,31,32], resulting in positively charged adatoms.…”

“…We simplify the potential landscape induced by the moiré by attributing a global minimum in the atop stacking area and the same height to hollow and bridge stacked regions. The repulsion is described by a screened Coulomb potential [34,35] since a pure Coulomb potential turns out to be too long-ranged, and dipolar interactions are too weak at the relevant distances, as estimated from dipole moments calculated for rare-earth atoms [31,32] and alkali metals [31,34] on freestanding graphene. The screening effect is due to the redistribution of the electrons in graphene around the charged adatoms, yielding a lower effective charge for the repulsion and a faster decay.…”

Superconducting properties in tantalum decorated three-dimensional graphene and carbon structures

“…Due to the nature of an exposed 2D electron system open to environment, many studies have been carried out in examining how adsorption of metal adatoms on graphene sheet can modify its electronic transport properties for electronics, sensors and energy applications [3][4][5][6]. Indeed, in tin decorated graphene sheets a tunable superconducting phase transition was observed [7].…”