Abstract text (incl. figure legends and references)

Recently the method of four-dimensional scanning transmission electron microscopy (4D STEM) imaging, where a focused beam of electrons scans the sample in a two-dimensional (2D) raster pattern, has gained significant interest and a continuous growing community. An ultrafast and direct electron detection system like the pnCCD (S)TEM camera [1] having single electron sensitivity is ideally suited for all kinds of 4D STEM applications. The pnCCD (S)TEM camera can be operated at 7500 frames per second, and is compatible with electron energies ranging from 20 keV to 300 keV.

With the possibility of coherent STEM imaging, enabling quantitative phase contrast imaging, the range of materials which can be analyzed with STEM has been extended down to light elements like carbon.

Attractive additional information about the sample like phonon or plasmon excitation or core loss phenomena can be obtained from electron energy loss spectroscopy (EELS). With the currently available detector systems, the decision needs to be made if either a 4D STEM or an EELS measurement is taken.

We present a new pnCCD chip design with a center hole in the middle of the detector (diameter 2.5 mm, see in Fig. 1), which lets the center part of the electron beam pass through into the EELS spectrometer, while the outer bright field disc as well as parts of the dark field signal can be observed on the pixelated 4D STEM detector simultaneously. Calculations have already shown that e.g. Ptychographic phase contrast reconstruction is very robust against loss of the center part of the bright field disc [2].

The contribution will show preliminary detector data and calculations using 4D STEM data.

Figure 1: Schematic showing the dimensions of the center hole in the pixelated 4 D STEM detector. The physical hole has a diameter of 2.5 mm, while the insensitive region in the detector plane has a diameter of 4 mm.

Figure 2: Picture of a pixelated 4D STEM detector with a center hole in the middle, which allows to combine 4D STEM and EELS measurements.

References:

[1] Ryll, H., et al, Journal of Instrumentation 11 (2016)

[2] Song B., et al, Physical Review Letters 121 (2018)