Modeling hot-electron generation induced by electron promotion in atomic collision cascades in metals

We present a computer simulation model for the investigation of electron promotion processes in atomic collision cascades in metals. The model combines molecular dynamics and molecular orbital calculations to describe the formation of hot electrons in close atomic collisions. We apply this model to a set of collision cascades initiated by the impact of a 5-keV silver atom onto an Ag(111) surface. The calculations show that about 15% of the bombarding energy originally introduced into the solid is dissipated into the generation of hot electrons in close collisions. Furthermore, we find that the nascent excitation energy spectrum closely resembles a power law $f\left(E_{\text{exc}}\right)\propto E_{\text{exc}}^{-\delta }$ with exponents $\delta \approx 2–3$.

Figure 1

(Color online) Diabatic MO energy versus interatomic distance of two silver atoms colliding within solid silver (taken from Ref. 4).

Figure 2

(Color) On-top view of the center of the (111)-oriented surface of the silver model crystal. The three uppermost atomic layers (solid circles), the two-dimensional Wigner-Seitz cell (solid line), and the 120 impact points within the irreducible zone of the Wigner-Seitz cell (small solid circles) are depicted. In addition, each impact point is colorized according to its individual sputter yield $Y$.

Figure 3

Average total excitation energy (left) and average number of hot electrons (right) per trajectory for different level widths $\Delta$.

Figure 4

(Color online) Total excitation energy generated by electron promotion as a function of impact point (additionally see Fig. 5).

Figure 5

Mapping from the index $k$ to the location of the corresponding impact point within the irreducible zone of the two-dimensional Wigner-Seitz cell.

Figure 6

Nascent excitation energy distribution of hot electrons generated in electron promotion events. The data has been taken from the set of 120 trajectories