Unraveling the Causes of the Instability of Au_n(SR)_x Nanoclusters on Au(111)

Properties of small metal nanoclusters rely on the exact arrangement of a few atoms. Minor structural changes can rapidly destabilize them, leading to disintegration. Here, we evaluate the energetic factors accounting for the stabilization and integrity of thiolate-capped gold nanoclusters (AuNCs). We found that the core-cohesive and shell-binding energies regulate the disintegration process on a solid substrate by investigating the different energetic contributions, as shown here in a combined experimental and theoretical study. As the AuNC size increases, the core-cohesive energy and shell stability (imposed by S-Au and hydrocarbon chain interactions) counterbalance the AuNC–substrate interaction and slow down the AuNC disintegration. Thus, the decomposition can not only be understood in terms of desorption and transfer of the capping molecules to the support substrate but conversely, as a whole where ligand and core interactions play a role. Taken together, our experimental and theoretical results serve as guidelines for enhancing the stability of AuNCs on solid-state devices, a key point for reliable nanotechnological applications such as heterogeneous catalysis and sensing.