Untitled - IAP/TU Wien - Technische Universität Wien

Nanostructure Characterisation by Electron Beam Techniques
Surface excitations in electron spectroscopy
F. Salvat-Pujol, 1,* W.S.M. Werner, 2 W. Smekal, 2 R. Khalid, 2 A. Bellissimo, 2
M. Novák 3 , J. Zemek 4 , and P. Jiricek 4
1 Insitut für Theoretische Physik, Goethe-Universität Frankfurt,
Max-von-Laue-Straße 1, 60438 Frankfurt (Germany)
2 Institut für Angewandte Physik, Technische Universität Wien,
Wiedner Hauptstraße 8-10/134, 1040 Wien (Austria)
3 Université Libre de Bruxelles, Service de Métrologie Nucléaire,
CP 165/84, 50 Avenue F. D. Roosevelt, B-1050 Brussels, (Belgium)
4 Institute of Physics, Academy of Sciences of the Czech Republic,
Na Slovance 2, 182 21 Prague 8, (Czech Republic)
*salvat-pujol@itp.uni-frankfurt.de
A quantitative understanding of electron spectra relies on an adequate description of electron energy losses
taking place both in the bulk of the solid and in the vicinity of the solid-vacuum interface (at either side of
the surface). Several models for electron energy losses near planar interfaces have been published in the last
three decades based on the semiclassic dielectric formalism (see references in [1]). However, these models
often include several simplifying approximations: some are valid for selected trajectories, others employ a
simplified dielectric response of the solid, etc.
A detailed model for surface excitations in electron spectroscopy has been derived within the semiclassic
dielectric formalism, encompassing other models in the literature and allowing one to investigate their
relevant physical assumptions. The model has been implemented in a Monte Carlo simulation of reflectionelectron-energy-loss
spectra (REELS). REELS have been simulated for 17 metals, obtaining a good
agreement with published experimental spectra in absolute units (typically within $\sim10$ \%).
The model has been further employed to interpret a series of recent electron energy-loss experiments. On the
one hand, it has been instrumental in exposing the role played by surface excitations in secondary-electron
emission in a recent measurement of a double-differential secondary-electron yield from polycrystalline
samples (Al, Si, Ag) employing a time-coincidence technique. On the other hand, it has been used to
interpret a series of angle-resolved REELS of a Au surface at grazing incidence [2]: it has been shown that
energy losses at the vacuum side of the interface constitute an essential contribution to electron energy-loss
spectra and must be accounted for in detail for a quantitative understanding of REELS.
References
[1] F. Salvat-Pujol and W.S.M. Werner, Surf. Interface Anal. 45 873-894 (2013).
[2] W.S.M. Werner et al, Phys. Rev. Lett. 110 086110 (2013).
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