Metal clusters and cluster doping with atmospheric pressure microplasma (?)

Atmospheric pressure microplasma have demonstrated great opportunities to synthesize nanoparticles with diameters reaching values well below 5 nm, which are for many materials a size range within the quantum confinement regime. The ability to synthesize and analyse clusters, e.g. with diameters below 1 nm, is scientifically intriguing but also important from many point of views. We have investigated cluster formation using an atmospheric pressure microplasma that uses a solid sacrificial metal wire and that has been very ‘prolific’ in the synthesis of metal and metal oxide nanoparticles. The formation of clusters is therefore an important step to understand the mechanisms leading to the nucleation and growth of larger particles. At the same time, metallic clusters have unique fundamental properties with relevance for many applications. Metal clusters also transcend accepted boundaries, for instance that between solid and liquid phases.
We report here our initial work to synthesize and understand metallic clusters, while providing some insights into the formation mechanisms of nanoparticles in atmospheric pressure plasmas. While our initial work was inspired by metallic tin clusters, we will also report our more recent work with bismuth. We report on the challenges to work with clusters, what we understand of their formation and some unexpected opportunities.