Cathodoluminescence has attracted interest in scanning transmission electron microscopy since the advent of commercial available detection systems with high efficiency, like the Gatan Vulcan or the Attolight Mönch system. In this work we discuss light emission caused by high-energy electron beams when traversing a semiconducting specimen. We find that it is impossible to directly interpret the spectrum of the emitted light to the inter-band transitions excited by the electron beam, because the Čerenkov effect and the related light guiding modes as well as transition radiation is altering the spectra. Total inner reflection and subsequent interference effects are changing the spectral shape dependent on the sample shape and geometry, sample thickness, and beam energy, respectively. A detailed study on these parameters is given using silicon and GaAs as test materials.

Central European Institute of Technology Brno University of Technology Purkyňova 123 Brno 612 00 Czech Republic

Central European Institute of Technology Brno University of Technology Purkyňova 123 Brno 612 00 Czech Republic; Institute of Physical Engineering Brno University of Technology Technická 2 Brno 616 69 Czech Republic

University Service Centre for Transmission Electron Microscopy Brno University of Technology Purkyňova 123 Brno 612 00 Czech Republic; Institute of Physical Engineering Brno University of Technology Technická 2 Brno 616 69 Czech Republic

University Service Centre for Transmission Electron Microscopy Technische Universität Wien Wiedner Hauptstraße 8 10 Wien 1040 Austria

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Fundamental Limit of Plasmonic Cathodoluminescence