This instrument is used a test bed for novel applications in diffractive imaging. For this purpose, it is equipped with full TFS STEM functionality, including a Panther segmented STEM detector. Controlled by a TVIPS USG scan generator, we will develop novel scan pattern and approaches to collecting diffractive data. The home-built EIGER detector is a collaboration with the team of Bernd Schmidt at the Paul-Scherrer Institute in Villigen, Switzerland. This 512x512 hybrid pixel detector can record frames at up to 8000 fps.
Ptychography is a method, in which a focussed electron beam of a slightly larger diameter (e.g., 20 nm diameter) is stepped over the sample in a raster pattern with overlapping beam positions, while a high-speed hybrid pixel detector records the electron diffraction patterns at each electron beam position. From the ensemble of the recorded patterns it is possible to later reconstruct the structure of sample. This involves extensive computational processing of the recorded data, since data are recorded in reciprocal (Fourier) space, while the final image is needed in real space.
Since the electron microscope operates in diffraction mode, high-resolution data can be recorded relatively easily. The challenge lies in establishing conditions, through which the recorded diffraction data can be combined into a phased dataset to yield useful real-space images. Recorded datasets are rapidly of gigantic dimensions, reaching a Terabyte in volume within few minutes. Online processing is therefore needed to immediately reduce the data volume to manageable sizes.
In collaboration with the team of Carsten Sachse (ER-C Jülich), we also develop integrated differential phase contrast (iDPC) or integrated Center of Mass (iCOM) 4D STEM approaches.