EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Understanding the functional properties of novel nanomaterials demands and exhaustive characterization effort based on state-of-the-art complementary techniques. This is important for those nanomaterials where different shape-morphology configurations bring in an interplay between bulk properties and surface- and edge- induced effects. In this context, transition metal dichalcogenides (TMD) nanomaterials such as molybdenum disulfide have attracted attention in a variety of fields due to their unique properties from metallic edge states to ferromagnetic behavior. Realizing this potential demands novel instrumental and detection techniques that achieve the highest possible spatial resolution. To this end, recent progress in the structural characterization of these TMD nanomaterials, using transmission electron microscopy, can be complemented with the precise charting of their local electric fields at the nanoscale.

Here, we correlate the structural properties with the local electric fields in low-dimensional TMDs by means of a brand-new measurements strategy on the Electron Microscope Pixel Array Detector (EMPAD). The EMPAD is a fast-pixelated detector with a high dynamic range that can record the unfiltered convergent beam electron diffraction (CBED) pattern at every scan position of the STEM probe, resulting in a four-dimensional dataset. TMD nanostructures are synthesized by means of chemical vapor deposition in a manner that makes it possible to control their size and morphology. The EMPAD allows the precise evaluation of the momentum transfer from the probe electrons due to the interaction with the sample. This information can then be directly translated into the local electric fields present within the sample and responsible for this momentum transfer. We thus demonstrate how the EMPAD enables a detailed mapping of the electric fields in TMD nanostructures, including their edges and point defects, providing complementary insights towards the full exploitation of the rich physical properties of TMD nanomaterials.