Abstract
This commentary explains the origin, principles, practical applications, and future perspectives of mass-selected ion beams generated using two rotating electric-field mass (REF-MS) filters as a formation of primary ion beams. Our team has been investigating the underlying principles of REF-MS separation and assessing the feasibility of developing suitable systems to realize mass separation and ion beam convergence using rotating electric fields as well as the practicability of this method. This commentary focuses on the mechanism observed cycloid trajectories followed by REF-MS-selected ions as a formation of primary ion beams. A focused ion beam column with Ga and AuGe liquid metal ion sources was introduced to REF-MS optics to assess the mass-selection performance as the filter. The column was then replaced with a vacuum electrospray ionization source, and the resulting mass-selected and/or cluster size-selected ion beam was used to create a microscale crater and Co elemental ring.
https://ror.org/05sj3n476 
