Metal Cluster Production by Condensation of Metal Vapour in Supersonic Expansions and by Aggregation in Droplets

Metal clusters have been produced by condensation of metal atoms on or inside small argon clusters and by collision of supersonic atomic argon beams with atomic metal vapours. A key parameter in both processes is the metal atom particle density. For iron, metal particle densities above a thermal open crucible-type evaporator were determined using quartz-micro-balance mass flux measurements, revealing a point-source-like dependence on the distance from the crucible. For silver atoms the particle densities were also determined using scattering from small argon clusters. Formation and soft-deposition of iron nanoparticles was first attempted using a supersonic beam of argon atoms that was blown into a vapour of iron atoms. Transmission electron microscopy showed the presence of iron nanoparticles whose size depended on the deposition time, showing that aggregation takes place after deposition. The deposition rates were of the order of 0.01 nm/s. In the second part of the study argon clusters containing on average 21 atoms were directed through vapours of xenon or silver atoms. Time-of-flight mass spectrometry showed the presence of xenon and silver clusters when the xenon or silver particle densities were increased. The xenon clusters contained up to four atoms whereas silver would only formdimers. The mass spectra also showed argon atoms attached to the xenon clusters, but not to the silver dimers, which was attributed to the high temperature of the silver dimers.