Focused Ion Beam Optics Driven by Sheath Nonlinearity and Wave-Plasma Interaction in Restricted Geometry

In recent years electromagnetic wave-driven plasma sources for focused ion beams (FIB) have attracted considerable attention1. However, developing such plasma sources for FIB is nontrivial and can pose mighty challenges. Often a micro-meter size beam needs to be extracted to maintain a small object size for demagnification, thereby demanding that the plasma source be as small as possible. The situation is exacerbated in case of microwave driven plasma sources because of geometrical cutoff limitation, which demands a minimum chamber dimension for wave propagation and subsequent plasma generation2. Additionally, the density cutoff limitation is encountered when the plasma frequency becomes larger than the wave frequency. The two limitations are often inextricably intertwined and pose considerable confrontation for wave-particle sustainability, often rendering surprising observations3.