Atomic-Scale Electron Microscopy of Two-Dimensional Matter: Defects, Interlayer Coupling, and Confined Reactions

Atomic-resolution electron microscopy reveals how defects, local coordination, and interlayer interactions shape the behavior of two-dimensional materials. This Review discusses selected advances in transmission and scanning transmission electron microscopy and electron energy-loss spectroscopy, with emphasis on graphene, hexagonal boron nitride, transition-metal dichalcogenides, and species confined within bilayer graphene. The discussion begins with specimen preparation and low-voltage operation, emphasizing the influence of contamination and electron irradiation on structural interpretation. Representative studies then illustrate how imaging and spectroscopy connect atomic configurations with bonding, electronic states, and functional responses. Particular attention is also given to spectroscopic signatures of interlayer coupling and show how bilayer graphene provides a confined environment for unusual atomic arrangements and beam-driven chemical reactions. These examples highlight the need to distinguish observed structures from inferred properties and irradiation-induced products. Finally, future opportunities in dose-efficient acquisition, depth-sensitive imaging, spectroscopy, and correlative measurements are outlined for understanding and controlling low-dimensional matter.