Pushing the limits of differential phase contrast microscopy - more than a mere facelift
Josef Zweck
Institut für Experimentelle und Angewandte Physik, Universität Regensburg
17:30 - 18:30 Tuesday 25 June 2019 Aula der TUGraz In contrast to its name, differential phase contrast (DPC) was initially interpreted as the deflection of a charged particle by a local field, in general a magnetic field within a specimen. Implicitly it was assumed that the field was constant over the extent of the electron probe with dimensions in the range of several tens of nanometers or larger. With this approach, DPC became a very well established technique to image micromagnetic structures.
Starting in 2012, DPC was applied for the first time to electrostatic fields, present in strained quantum well structures, to show its applicability for electric fields, too. Soon thereafter, experiments were conducted withprobe corrected microscopes and probe sizes down to 40 pm, smaller than typical interatomic distances. Now it became possible to probe the fields between atoms directly. However, these fields are by no means homogeneous, so the particle image for the interpretation was bound to fail. If under those conditions, one considers an electron as a quantum mechanical matter wave, the previous deflection of the beam now becomes a diffractive redistribution of intensities by self-interference, which can nowadays successfully and quantitatively be interpreted.
In this talk I will describe the development steps of DPC as sketched above and give examples for each stage.
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