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Master thesis: A reciprocity approach to four-dimensional Scanning Transmission Electron Microscopy

Advertising institute: ER-C-1 - Physics of Nanoscale Systems
Reference number: D030/2018, Physics

In transmission electron microscopy (TEM) two complementary imaging modes exist: scanning TEM (STEM), where an atomically sharp electron beam is rastered over the specimen, and conventional TEM (CTEM), where the specimen is illuminated with a plane wave.

A STEM image is formed by mapping a signal recorded in the diffraction pattern against the position of the scanning beam. In contrast, CTEM images are recorded in real space after several magnification steps.

Although both imaging modes are fundamentally different, they can be linked to each other via the so-called theorem of reciprocity.

With the advent of 4.dimensional STEM, where the whole diffraction pattern is recorded on ultrafast cameras at each position of the scanning probe, the reciprocity theorem has highly interesting implications to be investigated either with experimental or theoretical focus in this thesis.

Surprisingly, it enables the generation of CTEM images from 4D STEM recordings with a flexibility that the established CTEM mode does not offer. For example, TEM specimen are usually bent, so that the crystallographic orientation changes within the imaged area.

In a first step, you will be trained to record 4D STEM data for such specimen on contemporary electron microscopes. Using these unique recordings, a method is to be developed to calculate the local crystallographic orientation.

You will then use this information in combination with the reciprocity theorem to generate virtual CTEM images in which the effect of specimen bending is eliminated.

Finally, your work could address the benefits of this method on the mapping of crystal strain in, e.g., a semiconductor or a ferroelectric nanostructure.

The wealth of information in 4D STEM data sets welcomes your own ideas for further evaluations!

Your work is embedded in the international team of electron microscopists at the Ernst-Ruska-Centre within the moreSTEM group.

Contact person:
Dr. Knut Müller-Caspary
Forschungszentrum Jülich
Ernst Ruska-Centre for Electron microscopy