Chemical Analysis with Sub-A Resolution of Light Elements Using Aberration-corrected STEM
The last few years have seen a paradigm change in scanning transmission electron microscopy, STEM, with unprecedented improvements in both spatial and spectroscopic resolution being realized by aberration correctors, cold-field emission guns and monochromators. The successful correction of lens aberrations has greatly advanced the ability of the STEM to provide direct, real space imaging at atomic resolution. Very complementary to reciprocal space methods, this is especially advantageous for aperiodic systems, nanostructures, interfaces and point defects.
Aberration-correction has also enabled the development of new imaging techniques, such as incoherent annular bright field (ABF) imaging, which enables the direct visualization of light atoms, such as hydrogen. While these instrumentation developments have brought notable successes in materials analysis, in particular for hetero-interfaces, catalysis and thin-film studies, they have also challenged the established experimental protocols and our fundamental understanding of both imaging and spectroscopy in the STEM. Aberration correction also allows increased flexibility in choosing the appropriate electron energy to minimize beam induced damage while maintaining atomic-resolution (e.g. 60 keV electrons for studying graphene with 1.3 Å resolution).
Here, I will present the latest results from the new probe aberration-corrected cold-field emission JEOL JEM-ARM200CF at UIC, which allows in-situ characterization with 78 pm spatial resolution and an energy resolution of 350 meV in the temperature range between 10 K and 1,300 K using a variety of in-situ heating, cooling, tomography and electrical feedback holders. The primary electron energy can be chosen between 80 and 200 kV. I will show how low-energy imaging can now be used to characterize beam-sensitive materials without significant loss in spatial resolution and how such experiments enable direct correlation with other techniques, including atom-probe tomography and first-principles modeling.