Novel method for Ag colloidal cluster formation by laser ablation at the air–liquid interface

We report a novel method for formation of sub-nanoclusters by laser ablation at the air–liquid interface. The density of plasma induced by laser ablation at the air–liquid interface should be lower than that produced by laser ablation in liquid. In the lower density plasma, the produced clusters rarely grow or aggregate into larger clusters because the collision probability is low, resulting in the formation of small clusters. Ag sub-nanoclusters were observed by electrospray ionization mass spectrometry (ESI-MS) and X-ray photoelectron spectroscopy (XPS). These results show that low-density plasma can be applied to small-cluster formation and that laser ablation at the air–liquid interface produces a good reactive field for the formation of sub-nanoclusters. Our results highlight the importance of low-density plasma induced at the air–liquid interface for sub-nanocluster formation.