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E. Bodewits, K. Dobes, F. Aumayr, R. Hoeckstra:
"Secondary electron yield from HCI on Au and thin films of C₆₀";
Poster: 19th International Workshop on Inelastic Ion-Surface Collisions (IISC-19), Frauenchiemsee/Germany; 20.09.2012; in: "Book of Abstracts, 19th International Workshop on Inelastic Ion-Surface Collisions (IISC-19)", (2012), S. 84.

Recently we investigated the influence of C60 thin films
evaporated on Au(111) on the secondary electron yield of
highly charged ions (HCI) [1]. It was found that the relative
secondary electron yield from C60 follows an exponential
growth curve as function of the number of monolayers
(ML) and saturates at an increase of 35% for 5 ML of C60
on Au as shown in figure 1.
Recently the original over-the-barrier model was extended
by Lake et al. [2] by the inclusion of a thin dielectric film on
top of a metal surface. They showed that a highly charged
ion approaching an Al2O3 film may perturb the thin film
such that throughout the film the bottom of its conduction
band drops below the workfunction of the substrate while
the barrier between the HCI and the thin film is still that
high that over-the-barrier transitions between the film and
the HCI are not yet possible. In this way the insulating
aluminium oxide film effectively lowers the substrate workfunction
by a few eV. The earlier onset of the neutralization
and creation of hollow atoms will give more time in front of
the surface for the relaxation processes of the hollow atoms.
This would lead to an increase in the secondary electron
yields.
There might be another cause for the increase in the secondary
electron yield too, namely an increase in the escape
length of electrons produced below the surface. The thin
films of C60 have a very open structure, therefore electrons
produced in the C60 film may have a higher probability of
escaping and being detected as compared to electrons produced
below a closer packed Au surface.
Here we discuss further experiments concerning the increase
in secondary electron yield. In the new series of experiments
we investigated how changing the incidence angle
and the kinetic energy of the HCI affects the secondary electron
yield. Also, experiments with highly ordered pyrolytic
graphite (HOPG) have been done for comparison with the
C60 layers [3].