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Master thesis: Identification and correction of scan noise in atomically resolved charge density maps

Advertising institute: ER-C-1 - Physics of Nanoscale Systems
Reference number: D031/2018, Physics

In Scanning Transmission Electron Microscopy (STEM), a highly focused electron beam is rastered over the specimen in an electron microscope.

Thanks to aberration correction, STEM probes have nowadays achieved diameters as small as 50pm and thus enable the view inside atoms.

Recently, approaches have been developed to measure electric fields and charge densities at subatomic scales using 4-dimensional STEM. In this imaging mode, full diffraction patterns are recorded for each raster position of the probe.

In practice, however, the mapping of charge densities at sub-atomic scale is hindered by so-called scan noise. This means that the positioning of the STEM beam by the scan unit of the microscope deviates from a regular raster within the range of several picometres.

In this thesis, you will learn to acquire atomically-resolved 4D STEM data sets at contemporary electron microscopes. In a first step, the magnitude of the scan noise is to be determined for different settings of experimental parameters. Subsequently, you will use existing simulation software to study its impact on the measurement of charge densities.
Third, the scope of this master thesis includes pioneering work on the evaluation, implementation and testing of algorithms to correct the scan noise in 4-dimensional STEM.

Most importantly, we are looking forward to your ideas!

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