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Abstract:
Four dimensional scanning transmission electron microscopy (4D-STEM) is a powerful method for characterizing electron-transparent samples with down to sub-Ångstrom spatial resolution. 4D-STEM can reveal local crystallinity, orientation, grain size, strain and many more sample properties by rastering a convergent electron beam over a sample area and acquiring a transmission diffraction pattern (DP) at each scan position. These patterns are rich in information about the atomic structure of the probed volume, making this technique a potent tool to characterize even inhomogeneous samples. 4D-STEM can also be employed in scanning electron microscopes (SEMs) by placing an electron-sensitive camera below the sample. 4D-STEM-in-SEMs is ideally suited to characterize two dimensional (2D) materials and 2D-like van der Waals heterostructures (vdWH) due to their inherent thickness of a few nm. The lower accelerating voltage of SEMs leads to strong scattering even from monolayers. The large field of view and down to sub-nm spatial resolution of SEMs is ideal to map properties of the different constituents of 2D-like vdWH by probing their combined sample volume. We apply our 4D-STEM-in-SEM system to reveal the single crystallinity of MoS2 exfoliated with gold-mediation and determine the crystal orientation and coverage of both components of a C60/MoS2 vdWH.
