4D-STEM-in-SEM: Changing an SEM Microscope to a User-friendly Powder Electron Diffractometer.

Abstract

We describe recent improvements of our method named powder nanobeam diffraction in four-dimensional scanning transmission electron microscopy (4D-STEM/PNBD). The method can change an arbitrary SEM equipped with a 2D-array STEM detector to a user-friendly powder electron diffractometer. It reduces a 4D-STEM dataset to a single 2D powder electron diffraction pattern (using our Python package named STEMDIFF; https://pypi.org/project/stemdiff) and then to 1D radially averaged diffraction profile (using our Python package named EDIFF; https://pypi.org/project/ediff). Moreover, the EDIFF package can compare the final diffractogram with theoretically calculated X-ray diffraction patterns. Both STEMDIFF and EDIFF can be used in the form of simple interactive templates in Jupyter environment, which makes them accessible to common SEM users. The recent improvements in STEMDIFF and EDIFF (better dataset filtering, parallelization, and more flexible user interface) enabled us to analyze not only strongly diffracting nanocrystals but also samples with higher absorption and/or lower diffraction power. The final results obtained from 4D-STEM/PNBD datasets of all six samples analyzed in this contribution (two types of Au nanocrystals, GdF3 and TbF3 aggregates, and Fe3O4 nanoclusters with/without organic shell) were shown to be comparable with the results of the classical TEM/SAED method (selected area electron diffraction in TEM).