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Quantitative STEM & TEM
Aberration corrected STEM (Scanning Transmission Electron Microscopy) offers the framework to investigate the composition of a material as well as strain fields or defects present with a spatial resolution down to the atomic level.
The experimental data can be brought to an absolute intensity scale, reflecting the scattering power of each atomic column as shown in the experimental high angle annular dark field (HAADF) image (left-hand side of figure 1).
The experimental intensities can be compared to complementary contrast simulations carried out on a high performance computer cluster (see theoretical modelling).
If all experimental parameters are taken into account carefully, quantitative agreement between simulation and experiment can be achieved.
This allows to retrieve an atomically resolved map of the local composition as shown in the color-coded overlay of the HAADF image in Figure 1.
The recently installed pixelated detector allows to acquire a full diffraction pattern at each STEM scan point due to its high acquisition rate of up to 10.000 frames per second. The generated 4D datasets hold a rich variety of useful signals which cannot be addressed using a conventional HAADF detector. Among these are the angular distribution of the scattering as well as shifts in the diffraction plane which are introduced by electric fields present in a sample. Accompanied with adequate simulations quantitative information can be retrieved.
