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Zeitschriftenartikel:

M. Stöger-Pollach, C. Pichler, T. Dan, G. Zickler, K. Bukvisová, O. Eibl, F. Brandstätter:
"Coherent light emission in cathodoluminescence when using GaAs in a scanning (transmission) electron microscope";
Ultramicroscopy, 224 (2021), S. 1 - 6.



Kurzfassung englisch:
For most materials science oriented applications incoherent cathodoluminescence (CL) is of main interest, for
which the recombination of electron-hole pairs yields the emission of light. However, the incoherent signal
is superimposed by coherently excited photons, similar to the situation for X-rays in Energy-Dispersive Xray
spectra (EDX). In EDX two very different processes superimpose in each spectrum: Bremsstrahlung and
characteristic X-ray radiation. Both processes yield X-rays, however, their origin is substantially different.
Therefore, in the present CL study we focus on the coherent emission of light, in particular Čerenkov radiation.
We use a 200 μm thick GaAs sample, not electron transparent and therefore not acting as a light guide, and
investigate the radiation emitted from the top surface of the sample generated by back-scattered electrons on
their way out of the specimen. The CL spectra revealed a pronounced peak corresponding to the expected
interband transition. This peak was at 892 nm at room temperature and shifted to 845 nm at 80 K. The
coherent light emission significantly modifies the shape of CL spectra at elevated beam energies. For the first
time, by the systematic variation of current and energy of primary electrons we could distinguish the coherent
and incoherent light superimposed in CL spectra. These findings are essential for the correct interpretation of
CL spectra in STEM. The Čerenkov intensity as well as the total intensity in a spectrum scales linearly with
the beam current. Additionally, we investigate the influence of asymmetric mirrors on the spectral shapes,
collecting roughly only half of the whole solid angle. Different emission behaviour of different physical causes
thus lead to changes in the overall spectral shape.


"Offizielle" elektronische Version der Publikation (entsprechend ihrem Digital Object Identifier - DOI)
http://dx.doi.org/10.1016/j.ultramic.2021.113260


Erstellt aus der Publikationsdatenbank der Technischen Universität Wien.