Resonantly Enhanced Electromigration Forces for Adsorbates on Graphene

Abstract

We investigate the electromigration forces for weakly bonded adsorbates on graphene by using densityfunctional based calculations. We find that the nature of electromigration forces on an adsorbate critically depends on the energy level alignment between the adsorbate state and the Fermi level of the graphene. For a resonant adsorbate, whose frontier orbitals lie close to the Fermi level, the electromigration force is dominated by the electron wind force that is strongly enhanced along the electron flow direction, irrespective of the sign of the adsorbate charge. For a nonresonant adsorbate, the electromigration force is essentially the direct force that depends on the adsorbate charge. We also show that the magnitude of electromigration forces can be continuously tunable through electrostatic gating for resonant adsorbates. Our results provide new insight for understanding and controlling how nanoscale objects behave in or on host materials.

Electromigration Forces on Atoms on Graphene Nanoribbons: The Role of Adsorbate–Surface Bonding

“…On the other hand, for strong currents, for small gap GNR or graphene, the electronic resonance structure of the adsorbate can dominate the picture as shown in a recent study by Choi and Cohen. 14 The magnitude of the forces we found are in the order of 0.05−1 nN for fields of 0.15 V/Å, which is an order of magnitude lower than bond breaking forces reported, e.g., for Au−Au nanocontacts, 33 but might still be relevant in experiments. While the forces we found for metals like Al agree in magnitude and direction with previous results, 5 it will be interesting to see if the results presented for TM atoms such as Co are reproducible in experiments.…”

“…In the experiments by Preis et al, the heating due to the current passing through the Co-nanoribbon system into the Au(111) substrate is responsible for the nondirective Co motion. On the other hand, for strong currents, for small gap GNR or graphene, the electronic resonance structure of the adsorbate can dominate the picture as shown in a recent study by Choi and Cohen …”

“…In other works, bias-dependent adsorption energies and diffusion barriers were calculated. , In general, the electromigration force is divided into a contribution from the electric fieldthe direct forceand the interaction with the current flowthe wind force (Figure ). While the latter has been related to scattering of electrons by the adsorbate and the induced charge redistribution around the scatterer, − the direct force has mainly been derived from the charge transfer between the adsorbate and surface and the induced adsorbate charge. ,, Still, the understanding of the field-induced force is not extensive. While we have a classical understanding of metal atoms/clusters on surfaces in an electric field, where the force is related to the electric field via F = qE , with q being the atom charge, it is an open question as to whether this simple picture one would take from physics is enough to describe the behavior at the nanoscale.…”

Electromigration forces on atoms on graphene nanoribbons: The role of adsorbate-surface bonding

“…In the experiments by Preis et al [6] the heating due to the current passing through the Co-nanoribbon system into the Au(111) substrate is responsibe for the non-directive Co motion. On the other hand, for strong currents, for small gap GNR or graphene, the electronic resonance structure of the adsorbate can dominate the picture as shown in a recent study by Choi and Cohen [14].…”

“…1). While the latter has been related to scattering of electrons by the adsorbate and the induced charge redistribution around the scatterer [14][15][16], the direct force has mainly been derived from the charge transfer between adsorbate and surface and the induced adsorbate charge [5,14,17]. Still the understanding of the field-induced force is not extensive.…”