Atomic Level EELS Mapping Using High Energy Edges
Atomic Level EELS Mapping Using High Energy Edges in DualEELS™ Mode
Paolo Longo, Gatan, Inc.
Over the past few years, with the advancements in aberration-corrected transmission electron microscopy, the spatial resolution in scanning transmission electron microscopy (STEM) has been enormously improved. Such improvements that are the results of the reduction of the probe size and the dramatic increase of the probe current lead to the capability of acquiring high resolution elemental and chemical maps using EELS. Atomic level EELS maps can now be easily acquired and their acquisition time is to a large part related to the speed of the EELS spectrometer. The introduction of fast EELS spectrometers such as the GIF Quantum® has dramatically improved the information that can be obtained from a EELS Spectrum Imaging dataset. Now, EELS maps can be acquired at over 1,000 spectra per second which allows full advantage of the increased probe current available in an aberration probe corrected microscope to be realized. In addition the lens system present in the GIF Quantum®, with the capability to correct the aberration up to the 5thorder, leads to the ability of using high collection angles allowing more signal to enter the spectrometer while maintaining the energy resolution.
To illustrate these advances, data were acquired at Arizona State University using a probe corrected JEOL ARM 200 equipped with a Schottky FEG source operating at 200 kV. The EELS spectrometer used was a GIF Quantum®ER type spectrometer, including: DualEELS™ capability that allows two different energy regions of the EELS signal to be recorded simultaneously under the same experimental conditions; a 2K CCD camera that allows recording EELS data with an energy range that extends up to 2000 eV (4000 eV with DualEELS™); fast acquisition mode that allows acquisition of over 1,000 spectra per second; a 5th order aberration lens system corrected allowing large (>100 mrad) collection angles to be used with sub eV energy resolution.
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Images: a) Ti L2,3-edges elemental map; b) La M4,5-edges elemental map; c) Sr L2,3-edges at 1940 eV elemental map; d) Mn L2,3-edges elemental map; e) colorized map using the color scheme from Figures a-d.
