EELS is the art of sorting transmitted electrons according to their energy, precisely detecting them, and carefully interpreting the energy-loss spectrum.
Listed among the advanced microscopy techniques, EELS is certainly one of the most powerful characterization approaches in Materials Science. It combines the world-famous spatial resolution of a TEM with increasingly attractive spectral resolution.
A quick look at the Zero-Loss Peak (ZLP) relative intensity can reveal whether sufficiently thin sample regions can be obtained. Then, analysis of peaks that are present in the core-loss region (CL-EELS) can support the identification of chemical elements (even single atoms!) and the quantification of the local elemental composition. Thanks to a sufficient energy resolution, it is also possible to discern oxidation states with CL-EELS, as well as to retrieve local opto-electronic properties—such as a band gap and plasmons’ resonance frequencies—from the low-loss energy region (LL-EELS). All of this is done at the nm-scale, often limited by the inherent delocalization of the signal.
Recent improvements to monochromatic electron sources and EEL spectrometers’ stability currently allow the measurement of minute energy losses, including those that are related to atomic vibrations and local temperature. Today’s revolution in EELS is occurring through precise detection at the microscope’s bottom (or top!)—from the numerous full-energy electrons at the ZLP to the very few with high energy losses that contain the sample’s atomic fingerprint.
- A high dynamic range enables scientists to access the important information that is present at different energy ranges, from the ZLP to CL-EELS, with signals that often vary across six or more orders of magnitude.
- A point-spread function, optimized for the most common beam energies, guarantees sharp features and excellent performance for each set of experimental conditions.
- A high detection speed helps to overcome sample drift and damage, making it easy to acquire multiple spectra with a scanning electron probe.
Remarkable Examples
The EELS spectrum of h-BN at 60 kV. The charts show simultaneous collection of the ZLP and CL-EELS, without saturation, across 6 orders of magnitude.
Spectral imaging of STO/BTO/LSMO. Flexible elemental mapping with multi-pass EELS is made possible through zero readout noise.
Hybrid-Pixel Detectors for EELS
DECTRIS ELA
Most commercial TEM brands are compatible with Gatan Stela, which features DECTRIS ELA, or with CEOS CEFID, which can integrate DECTRIS ELA. Also, NION adopted DECTRIS ELA as the direct detector technology for its Iris Spectrometer.
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