Anomalous scaling behaviour of cobalt cluster size distributions on graphite, epitaxial graphene and carbon-rich (6√3 × 6√3)R30°

Abstract

The influence of the underlying interface on adsorption of cobalt (Co) is investigated by comparing the nucleation and growth of Co at room temperature on three carbon (C) surfaces, i.e. highly oriented pyrolytic graphite (HOPG), epitaxial graphene/SiC(0001) (hereafter abbreviated as EG) and precursor of EG i.e. C-rich (6√3×6√3)R30°/SiC(0001) (hereafter abbreviated as 6√3). On all three surfaces, Co adopts Volmer–Weber growth mode via formation of three-dimensional dome-shaped nanoclusters. Co clusters formed on 6√3 surface are smaller but denser than Co/HOPG or Co/EG. Scaling analysis reveals a critical nucleus size, i*=1 (atom) and the smallest stable cluster (i*+1) would be a dimer. Co/HOPG and Co/EG have the same order of magnitude for their cluster densities and sizes. Scaling analyses however show that the i* for Co/EG (i*=3) is larger than Co/HOPG (i*=0) and in this respect the smallest stable cluster would be tetramer and monomer respectively. This difference is attributed to the influence of an interface situated between graphene and SiC bulk. It appears that EG is more inert than HOPG towards the adsorption of Co and may act as a better substrate to host Co clusters.