Monte Carlo simulation of secondary electron emission from an N2-adsorbed layer on a Cu surface

Abstract

Surface adsorption of N2 molecules is a critical factor to limit the reduction of secondary electron (SE) yield (SEY) in many fields of applied physics. On the basis of the Polanyi potential theory, we describe a multi-layer N2 physical adsorption model to arrange the distribution of N2 molecules adsorbed on a Cu (110) surface. Considering six scattering types, we used a Monte Carlo method to develop a three-dimensional numerical model that simulated the scattering processes between electrons and adsorbed molecules. Thus, the SEY of a surface covered by an adsorbed layer could be obtained by statistical analysis of the final SE states. We found that the maximum of total SEY decreased exponentially with increasing N2 pressure between 0 and 0.1 Torr and decreased linearly with increased adsorbed layer thickness between 0 and 10 nm. The reduction in SEY was due mainly to the elastic scattering of large scattering angle and ionization of energy consumption in the scattering processes of electrons and adsorbed molecules. Accordingly, our model and results provide a powerful tool to fully understand the microcosmic mechanism of the SE emission of a metal surface with adsorbed layer.