First-principles evaluation of the secondary electron yield (γ ^N ) from polyethylene surface

Abstract

We have performed first-principles calculations (DFT) to estimate the secondary emission yield (SEY) through Auger neutralization mechanism (γ 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 γ 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 γ 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 γ N . Therefore a detailed sensitivity analysis has been included to address this problem. The results associated to metals have shown that γ 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 γ N coefficients similar to those of metals only slightly smaller.

Electronic structure of defected polyethylene for Schottky emission

“…beyond the surface, the potential energy becomes constant, and ε v has been estimated as the energy corresponding to this plateau. The same strategy has been widely used in previous studies [21,[56][57][58][59][60]. Geometry optimizations and scf loops were carried out by setting only one k-point in the Γ position of the Brillouin zone.…”

“…Collisions between these chemicals and the polymeric walls are considered as one of the main causes for treeing propagation [18]. The release of secondary electrons takes place through the Auger effect, and this process contributes to sustain the discharge [19][20][21]. The Schottky effect is the main discharge inception mechanism considered in a number of simulation tools for PDs such as [3,22,23].…”