Harder, better, faster, smaller: Instrumentation improvements for rapid in-situ EELS
Spectroscopic mapping by STEM-EELS is a powerful technique for determining the structure and chemistry of a wide range of biological, natural, and engineered materials and interfaces down to atomic resolution. The continual push for more robust, sensitive, and localized characterization is enabled by significant and ongoing improvements to hardware throughout the STEM-EELS instrument. At the same time, other developments in instrumentation and data processing have also opened the door of microscopy experiments to a wide range of in-situ stimuli, including heating and cooling, electrical biasing, and mechanical straining. Uniting these two fields of in-situ and high-resolution chemical microscopy offers the unique potential to explore phenomena at highly localized length scales that remain out of reach to other traditional probes. Despite recent promising hardware advances, however, most side-entry in-situ sample holders still suffer from some degree of reduced stage stability, such as large-scale directional drift arising from thermal gradients within the holder. High-resolution imaging techniques such as TEM or STEM imaging are still successfully employed under these reduced stability conditions through the rapid acquisition and subsequent registration of many image frames. EELS measurements, on the other hand, are limited by weaker scattering signals and have traditionally required much longer per-pixel dwell times, keeping them largely out of reach for in-situ experiments at the highest resolutions.
A newly developed extremely high brightness cold field emission source can squeeze currents of more than 1 nA in a sub-Å STEM probe. Harnessing this dramatic increase in signal with a new high frame-rate spectrometer and CMOS detector, we demonstrate atomic-resolution chemical and elemental mapping with more than a 10x decrease in per-pixel dwell times, paving the way for in situ and cryogenic experiments. This talk will discuss some techniques for successful in-situ EELS experiments, highlighting both progress and some remaining challenges for the EELS community.
Berit H. Goodge, School of Applied and Engineering Physics, Cornell University