Charge states of size-selected silver nanoparticles produced by magnetron sputtering

Gas-phase aggregation of metal nanoparticles (nanoclusters), in particular, produced by magnetron sputtering, is a widely used method in research and industrial applications. Therefore, better understanding of the nucleation and growth processes as well as of nanoparticle dynamics in aggregation zone is required. One of the poorly understood issues is a charge state of nanocluster formed in magnetron-based sources. In the current work, an original approach to study charge states of silver nanoclusters after mass (size) filtering is suggested. The study reveals that particles can carry both negative and positive charges; anionic nanoparticles dominate over the cationic ones under the conditions used in our experiment. It is also found that a considerable fraction of nanoparticles has charges greater than unity, and this fraction increases with particle size. However,the tendency depends on polarity. For the cations, the doubly, triply and quadruply charged nanoclusters have very similar fractions for a given filtering condition, while for anions, an ability to carry higher than unity charges by individual particles gradually decreases. Thus, the study provides important insights on the formation of cationic and anionic nanoparticles in magnetron cluster sources as well as on the tendencies to carry multiple charges depending on particle size.