Simultaneous EELS/EDS Composition Mapping at Atomic Resolution Using Fast STEM Spectrum-Imaging

Abstract

With advancements in aberration-corrected electron optics, the resolution in scanning transmission electron microscopy (STEM) has been significantly improved. More importantly, the reduction of the probe size and the increase of the probe current density enable the acquisition of elemental maps at the atomic scale in a fast manner using both EELS and EDS. With the latest generations of EELS spectrometers, atomic resolution compositional and chemical maps allow interfaces, oxidation state, and even single atoms to be examined with increasing detail. These improvements have also enabled elemental and chemical maps to be acquired rapidly using both low- and high-energy edges from elements across the periodic table, including heavy atoms such Au or Pt. On the EDS side, the introduction of large-area silicon drift detectors (SDD) has allowed these high-beam-current sources to be fully utilized. Improved detector area and support for higher count rates, compared to the previous generation of EDS detectors, allows the acquisition of EDS intensity maps from most types of material in the STEM, even for moderately thin samples. For the case of light elements, the reduced detector dead layer of SDD-based systems partially overcomes the very low florescence yield typical of low-energy X-ray lines. Also as reported in, atomic-level X-ray maps using fast detectors and bright sources can now be collected under some conditions. Because EDS and EELS provide complementary information about the sample, and are both generated with the electron beam, it would be wasteful to not acquire both datasets with every sample run.