Limitations of the friction model of low-energy electronic stopping

This is a follow-up on three recent studies of the significance of
impact-parameter-dependent electronic energy loss in the stopping of
low-energy ions in matter \cite{Sigmund17note,Shulga20,Schinner21}. With reference to the friction model of
electronic stopping we distinguish between two deviations from
velocity-proportional stopping, i.e., RM corrections -- which account for
nonuniform projectile motion during collisions --
and RED corrections which account for the influence of the
detector geometry on the output signal.
With the emphasis on RM
corrections we study gas and solid targets and, in particular,
conductor-insulator differences as well as projectile-isotope effects.
An important aspect is the interference
between RM and RED corrections, which was left out in our previous study
\cite{Schinner21}. Here
we find that the combined action of the two corrections is
{\em smaller} than the RM correction.