Speaker
Description
We are modeling the effects of a field enhancement factor (β) on the generated Fowler-Nordheim current using the Particle-in-Cell Direct Simulation Monte Carlo (PIC-DSMC) method for a vacuum environment. In the present work, we vary the DC voltage, and hence electric field, between two parallel Pt plates in which the modeled electrode surface elements are given a local work function and β by sampling probability density functions that are themselves functions of electrode material, preparation and conditioning, and surface topology. PhotoEmission Electron Microscopy (PEEM) and the combination of Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) measurements are used to infer work function and β distributions, respectively. Note that a model utilizing a fully resolved (nano- scale) topology would result in β=1 everywhere (assuming beta is solely a geometric enhancement factor). A coarsened scale (not nano-scale) β value is derived from the AFM/STM data by actually meshing the surface topology data and simulating an applied electric field to obtain local surface enhanced fields. We show that as the element size of our model grows, comparable field emission yields are obtained through the application of this effective β, rendering such an approach relevant to physical macroscopic dimensions that can be realistically meshed.