DOI: 10.1140/epjd/e2009-00256-8
Impact-parameter-dependent stopping of swift ions
II. Application to channeling
P. Sigmund1 and A. Schinner21 Department of Physics and Chemistry, University of Southern Denmark, 5230 Odense M, Denmark
2 Institut f. Experimentalphysik, Johannes-Kepler-Universität, 4040 Linz-Auhof, Austria
sigmund@ifk.sdu.dk
Received 13 May 2009 / Received in final form 2 September 2009 / Published online 3 October 2009
Abstract
Quantitative theory of the stopping of channeled ions needs
impact-parameter-dependent electronic energy loss as input.
In the previous paper, binary stopping theory has been expanded
to provide such data primarily for
the classical regime, i.e., for beam energies below 100Z12 keV/u.
The theory incorporates the Barkas-Andersen effect, charge-dependent
projectile screening and pertinent atomic properties.
A stringent test on the scheme is channeling measurements under
frozen-charge conditions, where minimum energy losses have been
measured. We have applied
the scheme to the
stopping of B, C, N, O and F ions in the (111) planar channel of Au, and
of F, Mg, Si, S and Cl ions in the [110] axial channel of Si.
The Si target has been characterized in terms of atomic charge
distributions for the three principal shells. The Au target has been
characterized by atomic charge distributions for all subshells except
the 6s electrons
which are described in terms of a homogeneous electron gas.
Better than 10% agreement has been achieved without the use of adjustable
parameters with experimental
data for 2 MeV/u ions in Au
and 3 MeV/u in Si for all measured charge states.
We find that a description in terms of the impact-parameter dependence
is essential in the analysis, in particular with regard to the
influence of the charge state. The discussion emphasizes the fact that
unlike in random motion, the stopping force follows a q12 relation
quite closely.
34.50.Bw - Energy loss and stopping power.
34.50.Fa - Electronic excitation and ionization of atoms (including beam-foil excitation and ionization).
61.85.+p - Channeling phenomena (blocking, energy loss, etc.).
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2009