Current-Induced One-Dimensional Diffusion of Co Adatoms on Graphene Nanoribbons

Abstract

One-dimensional diffusion of Co adatoms on graphene nanoribbons has been induced and investigated by means of scanning tunnelling microscopy (STM). To this end, the nanoribbons and the Co adatoms have been imaged before and after injecting current pulses into the nanoribbons, with the STM tip in direct contact with the ribbon. We observe current-induced motion of the Co atoms along the nanoribbons, which is approximately described by a distribution expected for a thermally activated one-dimensional random walk. This indicates that the nanoribbons reach temperatures far beyond 100 K, which is well above the temperature of the underlying Au substrate. This model system can be developed further for the study of electromigration at the single-atom level.

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

“…Our calculations are relevant in the low current regime and illustrate how the electronic redistribution in the bonds -rather than the direct interaction with the adsorbate charge -is important. 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].…”

“…In recent experiments, it has become feasible to place nanoparticles and even single atoms on surfaces, and study their diffusion using atomic resolution scanning methods like scanning electron microscopy (SEM) [5], scanning tunneling microscopy (STM) and atomic force microscopy (AFM) [6]. Besides mechanical manipulation by atomically sharp microscope tips, adsorbed particles can be moved by applying electrical fields, or, on conducting surfaces, by sending electrical currents through the structures, both causing electromigraton forces on the adsorbates [7].…”

“…Over the last decade, for both experimental and theoretical studies of atom migration, two-dimensional (2D) graphitic surfaces like graphene [5,8], graphene nanoribbons (GNRs) [6] and Carbon nanotubes (CNTs) [9][10][11], have gained interest due to their outstanding mechanical and electrical properties. Graphene-based materials exhibit a high stability and extraordinary, tunable electrical and thermal conductance properties [12], while their well-ordered 2D structure allows for an easy monitoring of surface migration processes.…”

“…Different theoretical models for bias-induced atom diffusion on 2D surfaces have been employed to explain the experimental results. Thermally activated diffusion has been suggested for single Co atoms adsorbed on GNRs, subject to a conducting STM tip [6]. In other work, biasdependent adsorbtion energies and diffusion barriers were calculated [11,13].…”

“…For our study, we chose Co, Al and Ag as adatoms, because these particular elements were part of previous (experimental) studies [5,6], as well as due to their different adsorption sites and very different chemistry. To provide detailed insight into the relation between forces and molecular orbitals, we focus on 3d transition metal (TM) atoms.…”