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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: 16th International Conference on the Physics of Highly Charged Ions (HCI 2012), Heidelberg/Germany; 03.09.2012; in: "Book of Abstracts, 16th International Conference on the Physics of Highly Charged Ions (HCI 2012)", (2012), S. 153.

In this contribution we discuss influence of C60 thin films evaporated on Au(111) on the secondary
electron yield of highly charged ions (HCI) (1). The experiments were performed using
IISIS, a future user station to be installed at HITRAP for investigations of HCI interacting with
surfaces. 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.
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 HCI 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).