A Monte Carlo calculation of the virtual source size for a liquid metal ion source

Abstract

We have developed a computer model to estimate the virtual source size of a liquid metal ion source. The ion trajectories were calculated using a Monte Carlo Computer code which included the effects of discrete Coulomb interactions. The analysis assumed the vacuum field of the sphere-on-orthogonal-cone (SOC) diode and used random numbers to simulate an ion emission process which had a Poisson distribution with full shot noise. Using the Monte Carlo generated trajectory data, we estimated the virtual source size by extrapolating trajectory tangents from reference planes normal to the emitter axis back to a plane containing the paraxial image of the virtual source. Extrapolation of the Monte Carlo computed virtual source size growth near the emitter predicts a virtual source size of 500–1000 Å at the extraction electrode.