  Low Energy Ion Scattering (LEIS) was employed to study the surface
composition of thin films of Ru on B, C and B4C films at different stages of
growth. Effects of surface segregation of C were observed. Previously unknown
matrix effects were observed in these samples, expressed in the decrease of
LEIS signals of Ru, B and C at low Ru concentrations. The effect disappears for
Ru-rich surfaces. Measurements with different He+ ion energies prove that the
characteristic velocities of the elements involved change with surface
composition. We suggest that these matrix effects appear due to the changes in
neutralization efficiency in quasiresonant neutralization from the valence band
(VB-qRN). This neutralization channel is present in elemental C and B due to a
wide valence band with energy states as low as -20 eV, which are in a
(quasi-)resonance with the He 1s level. This mechanism was earlier reported for
graphitic carbon. We suggest that it can be applied to a much wider range of
materials, leading to potential matrix effects in LEIS from a variety of
surfaces, containing B, C and potentially O and N atoms, e.g. borides,
carbides, oxides and nitrides, as well as alloys with B and C. This hypothesis
is supported by additional LEIS measurements on oxidized Ru which show matrix
effect in Ru-O LEIS signals as well. We argue that it is possible to avoid the
matrix effects from compounded surfaces within certain ranges of composition by
a proper choice of reference samples, while for other compositions knowledge of
characteristic velocities is required for reliable quantification.
