Presented by Huolin Xin
Center for Functional Nanomaterials
Brookhaven National Laboratory, Upton, New York
Scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) has proven to be a powerful technique to study structural, compositional, and electronic information of materials at the atomic scale. With the recent addition of 3rd-order and now 5th-order aberration correction, the numerical aperture can be opened up by a factor of 2-3, allowing sub-Angstrom resolution to be achieved in a STEM. Additionally, the enlarged numerical aperture couple with the use of a cold-field-emission gun provides a factor of 100x increase in the usable current for probing inelastic scattering events, while still maintaining an Angstrom beam size. This allows for the acquisition of 2-D compositional and bonding maps of both bulk and nanostructured materials at atomic resolution. In addition, with the development of differentially pumped gas cell inside a transmission electron microscope (TEM), we can now visualize solid-gas chemical reactions in situ. This capacity in both imaging atomic-scale reaction dynamics and acquiring spectroscopic fingerprints allows us to reveal reaction pathways that could not be resolved by any other approaches. Here, I will compare and contrast the complementary strengths and weaknesses of X-ray and electron probes and give a background on our techniques, including STEM, EELS, electron tomography, and in situ environmental methods, and will present studies centered around Pt-M3d bimetallic nanocatalysts before and after annealing, acid leaching, operational aging, gas oxidation, and reduction. I will also discuss the current challenges and future prospects for quantitative environmental TEM.
