Effects of model approximations for electron, hole, and photon transport in swift heavy ion tracks

TL;DR

This paper investigates how different assumptions and models affect the simulation of electron, hole, and photon transport in swift heavy ion tracks, highlighting the importance of collective response and photon transport in energy redistribution.

Contribution

The study systematically analyzes the impact of various model approximations on the kinetics of electronic subsystems in swift heavy ion tracks using the TREKIS code.

Findings

Effective one-band approximation matches experimental electron mean free paths in metals.

Collective lattice response dominates electron randomization and is temperature-sensitive.

Photon transport from core holes slightly accelerates energy redistribution but contributes minimally.

Abstract

The event-by-event Monte Carlo code, TREKIS, was recently developed to describe excitation of the electron subsystems of solids in the nanometric vicinity of a trajectory of a nonrelativistic swift heavy ion (SHI) decelerated in the electronic stopping regime. The complex dielectric function (CDF) formalism was applied in the used cross sections to account for collective response of a matter to excitation. Using this model we investigate effects of the basic assumptions on the modeled kinetics of the electronic subsystem which ultimately determine parameters of an excited material in an SHI track. In particular, (a) effects of different momentum dependencies of the CDF on scattering of projectiles on the electron subsystem are investigated. The 'effective one-band' approximation for target electrons produces good coincidence of the calculated electron mean free paths with those obtained in experiments in metals. (b) Effects of collective response of a lattice appeared to dominate in randomization of electron motion. We study how sensitive these effects are to the target temperature. We also compare results of applications of different model forms of (quasi-) elastic cross sections in simulations of the ion track kinetics, e.g. those calculated taking into account optical phonons in the CDF form vs. Mott's atomic cross sections. (c) It is demonstrated that the kinetics of valence holes significantly affects redistribution of the excess electronic energy in the vicinity of an SHI trajectory as well as its conversion into lattice excitation in dielectrics and semiconductors. (d) It is also shown that induced transport of photons originated from radiative decay of core holes brings the excess energy faster and farther away from the track core, however, the amount of this energy is relatively small.