Ion energy distribution near a plasma meniscus for multielement focused ion beams

Abstract

The axial ion energy spread near a plasma meniscus for multielement focused ion beams is investigated experimentally in atomic and molecular gaseous plasmas of krypton, argon, and hydrogen by tailoring the magnetic field in the region. In the case of magnetic end plugging, the ion energy spread reduces by ∼50% near the meniscus as compared to the bulk plasma, thereby facilitating beam focusing. A quadrupole filter can be used to control the mean energy of the ions. Comparison with standard Maxwellian and Druyvesteyn distributions with the same mean energy indicates that the ion energy distribution in the meniscus is deficient in the population of low and high energy tail ions, resulting in a Gaussian-like profile with a spread of ∼4 and ∼5 eV for krypton and argon ions, respectively. By carefully tuning the wave power, plasma collisionality, and the magnetic field in the meniscus, the spread can be made lower than that of liquid metal ion sources, for extracting focused ion beams of other elements with adequate current density, for research and applications in nanosystems