Optics of ion emission from the nano-aperture ion source

The optics of ion emission from the nano-aperture ion source were studied in the limit of a rarefied gas. In this limit the ions do not interact with neutral particles or other ions and the emission optics are determined by the electric fields, the distribution of ionization location, and the thermal energy distribution of the particles. A first order lens effect and two types of aberrations are identified. One aberration is associated with the initial energy distribution of the ions and a second aberration is caused by the initial spatial spread in the direction of the optical axis. Simple equations are derived, which enable estimates of these optical effects. Good performance is in general achieved when the fields inside and outside the chip are equal and above 3 kV/mm.