Orbital Mapping by STEM-EELS

The shape of electron orbitals influences properties on the atomic, as well on the macroscopic scale. Despite their importance, however, there are only very limited possibilities of directly investigating individual orbitals inside a specimen so far. While orbital mapping with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) was found to be possible [1], two major challenges related to the inherently poor signal-to-noise ratio (SNR) and the required low symmetry of the samples prevented more routine studies.
This FWF-funded PhD-project tries to overcome these visualization issues. The symmetry problem will be approached by performing measurements close to interfaces, defects or crystal with low symmetry. The SNR issue can hopefully be tackled by working with the latest generation direct-electron detectors used for STEM-EELS experiments. The influence of other experimental parameters such as sample thickness, acceleration voltage, aperture sizes, dispersion, etc. will also have to be tuned to optimize feature visibility. Further, a robust workflow for post-processing spectrum images with low SNR will be developed.