Charge state dynamics of keV ions in solids

TL;DR

This study experimentally investigates the charge state dynamics of keV ions in solids, revealing how electron transfer processes influence energy dissipation and ionization during ion transmission through silicon membranes.

Contribution

It provides new experimental data and analysis on charge state distributions and electron promotion processes for slow ions in crystalline solids.

Findings

Charge state distributions vary with velocity and trajectory.

Energy deposition is linked to electron promotion and ionization density.

Complex deexcitation mechanisms affect observed charge states.

Abstract

Fast dynamic processes between electrons in solids and a foreign atom represent a fundamental challenge for describing interactions in many-body systems and are a prerequisite for modelling materials modification. We experimentally determined the charge state distributions of slow He and Ne projectiles after transmission through thin single-crystalline silicon membranes. We found strong differences in velocity scaling and magnitude of the mean charge along different characteristic particle trajectories, providing direct insight on electron promotion and transfer processes inside the solid. Calculations of characteristic trajectories confirm the frequent spatial and ultrafast temporal accessibility of excitation channels commonly considered characteristic for large angle collisions. The commonly observed excess in energy deposition in amorphous targets compared to channelling trajectories and ab-initio calculations can thus be unambiguously linked to energy dissipation in frequent electron promotion as well as increased ionization density along the trajectory, driven by increased mean charge states. A quantitative comparison of energy loss and observed mean charge states further indicates complex deexcitation mechanisms at large interatomic distances masking the true equilibrium charge states along random trajectories.