  One-dimensional diffusion of Co ad-atoms on graphene nanoribbons has been
induced and investigated by means of scanning tunnelling microscopy (STM). To
this end, the nanoribbons and the Co ad-atoms 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.
