Advanced TEM insights into electronic landscape of complex van der Waals nanostructures*

Investigating the intricate electronic properties of complex van der Waals nanostructures, such as twisted two-dimensional (2D) materials and one-dimensional molybdenum disulfide (1D-MoS₂), reveals a tantalizing interplay of bandgap energy modulation and heterostrain effects. We present a comprehensive study that elucidates the profound sensitivity of bandgap energy to local heterostrain fields, thickness in twisted WS₂, and spatial variations in 1D-MoS₂ nanostructures. Our approach integrates high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) with electron energy-loss spectroscopy (EELS), further enhanced by machine learning. This synergy unravels up to 20% enhancements in the bandgap energy for twisted WS₂ nanostructures and distinctive excitonic behavior in 1D-MoS₂, including localized exciton peaks and spatially dependent bandgap modulations. Furthermore, advanced TEM techniques spotlight the crucial role of curvature-induced local strain fields in bandgap tuning. Our findings forge a profound understanding of the electronic characteristics within complex van der Waals nanostructures, underscoring the potential of advanced TEM methodologies. This work sets a foundational benchmark for twistronics, nanophotonics, optoelectronics, and the broader nanoscience domain.