Secondary electron yield of Cu (1 1 0) with adsorbed nitrogen: a 3D Monte Carlo simulation

Abstract

We developed an adsorption model to examine secondary electron (SE) emission from a surface adsorbed by N2 molecules. In this model, the scattering processes of electrons and N2 molecules are simulated by Monte Carlo method. The traces of both primary electrons (PEs) and SEs are tracked by combining the electron scattering in the material and adsorbed layer. The SE yield (SEY) is then calculated from the final states of electrons that can emit out from the adsorbed layers. Moreover, the effects of the work function variation induced by adsorption are also taken into account in the model. The SE emission properties of the surface under different pressures and surface coverage are examined by our adsorption model. We find that the SEY reaches its minimum for an intermediate coverage of 1 ~ 2 × 1015/cm2 for the Cu substrate. Further investigations on returning and outgoing ratios and energy distributions of SEs indicate that an adsorbed layer can generate new electrons but weaken the electron energy, especially at a high PE energy. The competing mechanism of ‘SE generation event’ and ‘energy losing event’ controls the variation of SEY. Accordingly, our model could serve as a powerful tool and our results can provide comprehensive insight into the SE emission of the surface covered by gas molecules, thereby helping us to find a rationale for the behaviour of SEs under various surface conditions.