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71st IUVSTA Workshop
Secondary-Electron Electron-Energy-Loss Coincidence Measurements
on Polycrystalline Aluminum
Alessandra Bellissimo, 1,* Wolfgang S.M. Werner, 2 F. Salvat-Pujol, 3 Rahila Khalid, 4
Mihaly Novák 5 and G. Stefani 6
Institut für Angewandte Physik, Vienna University of Technology, Wiednerhauptstraße 8-10/134, A-1040, Vienna, Austria
*bellissimo@iap.tuwien.ac.at
The double-differential secondary electron-electron energy loss coincidence spectrum of Al
has been measured for 100 eV primary electrons and energy losses between 0–25 eV. This energy
loss range comprises the simple scattering regime of energy losses and therefore allows one to
gain unique insight in the creation of secondary electrons (SE) in the course of excitation of
single surface and bulk plasmons in Al.
The experiment was performed in a UHV-system containing a hemispherical mirror
analyser (HMA) for the detection of the fast backscattered electrons and a time-of-flight (TOF)
spectrometer with an acceptance angle of approximately 2! for the slow secondaries, which are
detected in coincidence with the backscattered primaries.
The acquired double-differential coincidence spectra show very specific regions
corresponding to different excitation processes. In the low-energetic loss region - between the
work function delimitation and the bulk plasmon energy – the energy losses can be entirely
attributed to surface excitations, where also contributions of super-surface scattering can be
identified.
At the energy loss corresponding to the bulk plasmon excitation, a sudden and unexpected
transition can be observed, leading to a decrease of intensity. This is due to the increment of
depth range where the SE are emitted from. The region beyond the bulk plasmon characteristic
energy loss is dominated by the multiple inelastic scattering regime. The remarkable similarity of
coincidence TOF-spectra for the energy loss range 0–25 eV with the single TOF-spectra shows
that the main difference in the cascade regime is caused by the multiple excitations of bulk
plasmons. Consequently, through the analysis of the SE spectrum measured in coincidence with
surface and bulk plasmon losses a much more detailed picture concerning the contribution of
plasmon decay to the emission of secondaries can be attained.
References
[1] W.S.M. Werner, F. Salvat-Pujol, W. Smekal, R. Khalid, F. Aumayr, H. Störi, A. Ruocco and
G. Stefani, Appl. Phys. Lett. 99, 184102 (2011)
[2] Wolfgang S.M. Werner, Mihaly Novák, F. Salvat-Pujol, Josef Zemek and Petr Jiricek,
Phys. Rev. Lett. 110, 086110 (2013)
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