Ute Kaiser1
University of Ulm1
Quantum effects in 2D materials can manifest at very different length scales. Charge density waves, magnetic ordering, interlayer excitons are now studied also to understand their atomistic origin. Moreover, starting from exciting properties of low-twist angle graphene, twisted transition metal dichalcogenides are now explored, whereby the future of moiré superlattices is also dependent on reliable twist angle control. Here we show advances in sample preparation as well as that the electron probe in our low-voltage-tuneable spherical and chromatic aberration-corrected transmission electron microscope is a powerful tool to measure and, knock-on-damage-threshold-assisted, introduce structural and chemical variations in free-standing 2D materials on the atomic scale. Together with quantum-mechanical calculations their new properties can be understood<br/>Such we report on electron-beam-induced defects and their electronic properties and follow the migration paths and associated property changes in a variety of single and few-layered free-standing structures of transition metal di-chalcogenides (TMDs) and transition metal phosphorus tri-chalcogenides (TMPTs). In addition, we investigate the twist-angle-dependent moiré pattern formation in bilayers of TMDs by theoretical prediction-followed TEM experiments. From the comparison of monolayer, bi-layer and 2° twisted bilayer experimental images we determine twist-angle-induced inhomogeneous stacking-related localized strain in the layers as well as the twist-angle-induced changes of the interlayer excitons located in the low-loss range of the EELS spectrum. On the more fundamental base, we show that differentiating between the bond nature of two metal atoms is now possible when confined in the narrow space of a single walled carbon nanotube and that we begin to image lattice vibration in TEM.