Femtosecond dynamics – snapshots of the early ion-track evolution

Abstract

The energy dissipation and femtosecond dynamics due to fast heavy ions in matter is critically reviewed with emphasis on possible mechanisms that lead to materials modifications. Starting from a discussion of the initial electronic energy-deposition processes, three basic mechanisms for the conversion of electronic into atomic energy are investigated by means of Auger-electron spectroscopy. Results for amorphous Si, amorphous C and polypropylene are presented and discussed. Experimental evidence for a highly charged track region as well as for hot electrons inside tracks is shown. As follows mainly from Auger-electron spectroscopy, there are strong indications for different track-production mechanisms in different materials.

Introducing electron capture into the unitary-convolution-approximation energy-loss theory at low velocities

“…The transfer of target electrons to the bound projectile state (electron capture) leads to a so-called capture-and-loss cycle, where the captured electron is lost by the projectile in a subsequent collision, involving a projectile energy loss as well. The influence of electron capture depends strongly on the projectile charge state and, specifically at low velocities, on matching conditions for the electronic energy levels of the target and the projectile (resonant or nonresonant electron capture) [3]. The electroncapture cross section is exactly zero for antiprotons (because of the negative projectile charge), it is small for asymmetrical systems such as protons on helium (due to nonresonant capture processes), but resonant electron capture (specifically for * schiwietz(at)helmholtz-berlin.de homonuclear systems such as H + +H) involves enormous total cross sections.…”