Energy Dependence of Total Cross Section for Scattering of Helium Atoms from Isolated Atomic Steps

Abstract

The scattering of helium atoms from growing metal. surfaces is dominated by the interaction
between incident atoms and isolated surface steps. Understanding the process has been constrained
by the lack of both a realistic interaction potential and a satisfactory method for treating the
scattering from a defect, which, because of the height difference of the adjoining terraces, extends
to infinity. We have calculated step scattering cross sections for Cu(001) surface. The calculations
make use of realistic potentials that reproduce the scattering from low index planes and are created
from non-spherical, pairwise repulsive and attractive terms. The step scattering is isolated from that
of adjoining terraces using the linearity of summation of scattering amplitudes in the single
scattering regime. The results for equivalent step and terrace-site potentials give a total cross
section significantly less than the experimental value. The total cross section increases with helium
beam energy, contrary to the expectations that it is dominated by scattering from the attractive part
of the potential. The present work confirms the prediction of our previous study that not the Van
der Waals interaction but the hard wall of the scattering potential dominates the step scattering.

Key words: Energy dependence; Scattering; Helium atoms; Atomic steps

DOI: 10.3329/jbas.v34i1.5489

Journal of Bangladesh Academy of Sciences, Vol.34, No.1, 23-31, 2010