Method to measure the size distribution of massive cluster ion beams using two rotating electric fields

We developed a gas cluster ion beam (GCIB) source in conjunction with a two rotating electric fields (REFs)-type mass filter. The REFs method is suitable for a mass filter of a massive cluster ion beam because masses can be separated from a continuous ion beam with a constant mass resolution in all mass ranges. In principle, the mass range is unlimited. Using this apparatus, we measured the size distribution of an Ar cluster ion beam. The REFs method has a wide mass range of at least 40 ∼ 160,000 Da. The peak cluster size of the Ar cluster ion beam generated in this apparatus is 900. The annular patterns projected onto a fluorescent screen by Ar+ indicate that the maximum estimated mass resolution (M/ΔM) for the REFs mass filter is 86 for the full width at half maximum (FWHM) at a beam diameter of 0.12 mm ø. This mass filter should realize new applications of size-selected massive cluster ion beams as well as the study of cluster physics.