Mapping potential energy landscape of a probing atom in a complex surface environment

We have mapped the potential energy landscape for a Ag atom around Ag clusters on Si(111), via positioning a probing atom in the vicinity of clusters and monitoring the subsequent thermal motions with scanning tunneling microscopy. Both the probing atom's modulated diffusion and its combination with the clusters are quantitatively measured in a wide temperature range, showing strong dependence on the cluster size as well as specific sites. The atom-cluster interactions, as large as over 200 meV, are determined and found to alternate between attraction and repulsion at different separations. The demonstrated ability of studying atomic scale dynamics of single adsorbates in complex environments can provide opportunities to understand various phenomena in nanostructure growth and nanocatalysis.