Electronic energy loss processes for slow H and He ions in metals and insulators: new insights

TL;DR

This paper investigates electronic energy loss mechanisms for slow hydrogen and helium ions in metals and insulators, revealing how electronic structures influence stopping power at low velocities.

Contribution

It provides new insights into the roles of d-electrons and charge exchange processes in electronic stopping of ions in different materials.

Findings

d-electrons affect H ion stopping only when the d-band reaches the Fermi level

He ion stopping involves d-bands below the Fermi energy

Charge exchange cycles may explain low-threshold stopping in insulators

Abstract

Electronic stopping of H and He ions in metals and insulators is analyzed at velocities below 0.2 atomic units, i.e. below 1 keV for H and below 4 keV for He. In metals, stopping of H ions is affected by d-electrons only when the d-band extends up to the Fermi energy; for He ions, also d-bands well below the Fermi energy contribute significantly to electronic stopping. In insulators, the low threshold velocity for electronic stopping cannot be explained by electron-hole pair excitation; charge exchange cycles, however, may govern the threshold behavior of electronic stopping in ionic crystals.