08. Jun. 2017, 16:00 Uhr, Gebäude NW1, Raum H3
Vorstellung/Habilitationsabsicht: From strain to atomic electric fields: Exploring the room at the bottom by momentum-resolved electron microscopy
Dr. Knut Müller-Caspary, Univ. Antwerpen, Belgien
By focusing electrons on probes with a diameter of 50 pm, aberration-corrected scanning transmission electron microscopy (STEM) is currently crossing the border to probe subatomic details. Despite this revolution in spatial resolution, imaging modes in the field of electron microscopy remained essentially static over the past decades, and predominantly probe the structure of materials. In this work, momentum-resolved STEM is presented as a new imaging mode to map atomic electric fields and charge densities by electron microscopy. In particular, full 2-D diffraction patterns are recorded for a probe scanning over a 2-D raster which results in large 4-D data sets with millions of diffraction patterns. It is demonstrated in theory and experiment how subatomic electric fields can be measured from the highly complex intensity distribution in diffraction space by basic quantum mechanics. In addition to recent measurements of atomic electric fields and charge densities in 2D materials, this contribution comprises the development of momentum-resolved electron microscopy at Bremen University in the past 5 years. This involves high-precision strain and compositional analysis, as well as establishing ultrafast cameras operating at several thousand frames per second.