4D Scanning Transmission Electron Microscopy
4D Scanning Transmission Electron Microscopy (4D-STEM) is a powerful tool for characterizing material properties.
In 4D-STEM, a focused electron beam sequentially scans an electron-transparent sample area. The transmitted electrons form a diffraction pattern and are recorded with an electron-sensitive camera at each scan point. This maps properties such as crystal symmetry, lattice parameters, and strain. It's adaptable to standard SEMs, making it ideal to characterize thin samples like 2D materials and suspended 2D-like Van der Waals heterostructures due to its sub-nm spatial resolution and large scan area of up to several mm².
In this specific experiment, an in-house developed system collected 4D-STEM datasets in a SEM. The transmission diffraction stage (TDS) comprises a SMARPOD 110.45.2 sample stage for moving the sample with 6 degrees of freedom, an electron-sensitive camera inside the SMARPOD, a detachable sample holder for TEM grids, and additional components, including a linear stage (SLC-1750-S-HV) and copper components for heat dissipation.
The SMARPOD 110.45.2 specifications included a minimum accessible range of motion in z (beam direction) of ±5 mm, in x and y of ±8.0 mm, and a minimum accessible range of sample tilt around x and y of ±9.5°. Due to the experimental setup, the range of motion of the SMARPOD was limited. The SMARPOD and linear stage were essential to accurately position the sample and adjust the camera length(the distance between the sample and the camera) to ensure optimal sample positioning and movement, resulting in high quality and fast data acquisition.
More information can be found in the research article 'Probing Crystallinity and Grain Structure of 2D Materials and 2D-Like Van der Waals Heterostructures by Low-Voltage Electron Diffraction' by Johannes Müller. DOI: 10.1002/pssa.202300148