The role of dimers in the efficient growth of nanoparticles

The early stage of nanoparticle formation in gas aggregation systems is studied with the ambition to reveal the role of atomic dimers acting as cluster nuclei. The initial formation of a dimer nucleus, serving as a seed for subsequent atom attachment growth, is believed to be the bottleneck of the nanoparticle gas-aggregated synthesis. We thus examined the nature of the underlying process by employing energy-resolved mass-spectrometry and imaging of deposited nanoparticles. The production of dimers with origin in the discharge gas phase (ArCu+, Ar2+) and dimers preferentially sputtered directly from the target (Cu2+) was studied. The study demonstrates that sputtered Cu2+ dimers, carrying the high energy tail of Thompson energy distribution, play a major role as agents responsible for the formation of initial cluster nuclei, followed by a significant contribution of ArCu+; the population of these dimers is proportional to nanoparticle transported mass to the substrate. The proposed mechanism and the role of the dimer might be material independent since the qualitative agreement was also obtained for Ag NPs.