Charged Electrospray Beam Optics in the Focusing Column

Electrospray ionization process introduces a source of uniform submicron-sized nanodroplets for energetic bombardment of material. In addition to narrow size distribution, other fundamental characteristics such as low charge to mass ratio and high conductivity makes the beam of ES nanodroplets a suitable source for nano-scale microfabrication techniques such as sputtering and etching. ES beam focusing is required to achieve high energy density needed for such applications.
We studied the optics of charged ES beam in electrostatic field of an experimental apparatus. A numerical simulation of projectile trajectory in the axisymmetric electrostatic field determines the Gaussian image of the source. In addition to tracing algorithms, numerical models of potential error sources, geometric and chromatic aberrations, are used to inspect the bombarded area on silicon targets for a range of accelerating voltages. The deviated size and shape of the sputtered area from Gaussian image is used to track the imperfections in the experimental setup and the inherent properties of the beam. In our presentation we discuss how each of these aberration components affects the resolution, and can be corrected or minimized using additional elements such as multipole lenses.