Abstract
Gold nano-clusters were grown on chemically modified graphene by direct sputter deposition. Transmission electron microscopy of the nano-clusters on these electron-transparent substrates reveals an unusual bimodal island size distribution (ISD). A kinetic Monte Carlo model of growth incorporating a size-dependent cluster mobility rule uniquely reproduces the bimodal ISD, providing strong evidence for the mobility of large clusters during surface growth. The cluster mobility exponent of −5/3 is consistent with cluster motion via one-dimensional diffusion of gold atoms around the edges of the nano-clusters.
Highlights
We show that large clusters are able to move on the time scale of the growth and that this motion profoundly influences the island size distribution (ISD), producing a characteristic bimodal distribution
This cannot be reproduced by kinetic Monte Carlo (KMC) modelling with conventional processes and so we introduce a size-dependent cluster mobility
The chemically modified graphene (CMG) was prepared by a modified Hummers method, resulting in mainly single-sheet graphene oxide which was mounted on standard lacy carbon transmission electron microscopy (TEM) grid supports.[15]
Summary
The study of material nucleating and growing on a solid surface has a history of many decades, ranging from the thermodynamics of liquid droplets on solids to contemporary molecular dynamics simulations at the bio-materials interface.[1,2,3,4,5,6,7] Deposition and growth systems are typically characterised by huge ranges of time and length scale: the microscopic processes of surface growth (atomic length scale, time scale ∼10−12 s) aggregate to produce thin films, clusters or patterns with length scales from nm to μm over time scales of seconds or minutes.[8,9] While the microscopic processes are not usually directly accessible to experiment, their nature can often be inferred from the statistical properties of the grown material, for example, the island size distribution (ISD)[1] or the spatial distribution of islands[10] and their associated capture zones.[11]. The model is based on a simulation grid on which islands (Au nano-clusters) and monomers (Au atoms) can diffuse and interact.
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