Clusters

The seeded supersonic nozzle source uses an oven to evaporate metal into a reservoir of carrier gas. The gas-metal vapour mixture is then passed through narrow nozzle.

The supersonic expansion from the nozzle, into a vacuum, leads to rapid cooling of the mixture and clustering of the metal. This type of source is mostly used to produce intense beams of low boiling point metals. It produces continuous beams, with narrow speed distributions. The temperatures of the clusters it produces are not well known, but for larger clusters it is assumed to be near the evaporation limit.

Although the seeded supersonic nozzle source can produce cluster beams with higher intensities than other sources, it produces smaller clusters of up to 100 atoms. Under optimal conditions it can however be used to produce alkali metal cluster beams with 1000's of atoms.

In this source the cluster formation is controlled by thermodynamic processes, and as a result the relative abundances of different cluster sizes are governed by the binding energies. This means that a mass spectra of the beam will be structured, reflecting the variations of binding energy with cluster size.