First-principles evaluation of the secondary electron yield γN from polyethylene surface

We have performed first-principles calculations (DFT) to estimate the secondary emission yield (SEY) through Auger neutralization mechanism (gamma(N)) related to the impact of a series of ions on a polyethylene surface. We have considered many relevant ionic species, such as Ar+, which is often used as a benchmark. Our main goal is to study dielectric surfaces but, to check the validity of our approach, we have also considered some metallic surfaces (Al, Cu, Cu:N, Cu:O and CuO) on which some more experimental data can be found. On the contrary, very few references are available regarding the Auger neutralization on insulating materials and, in particular, on polyethylene. The SEY outcomes for metals have basically reproduced the experimental references. In particular, the same decrease in gamma(N), which has been associated to a 'dirty' (gas-exposed) metal surface, was confirmed by calculations. Thus, the applicability of the method to plastic material was considered to give realistic results. The computed gamma(N) values associated to polyethylene are in the order of 10(-1) for most of the ionic species here considered. Moreover, we have observed that a few percentage points of variations of the surface energy levels predicted by DFT calculations, may cause, depending on the ion type, a substantial change of gamma(N). Therefore a detailed sensitivity analysis has been included to address this problem. The results associated to metals have shown that gamma(N) variations are, for some types of ions, very sharp, while this variability is milder for a polyethylene surface. Our calculations are fully compatible with the previous relevant literature and suggest that plastic materials are characterized by gamma(N)coefficients similar to those of metals only slightly smaller.