Domains and Topological Defects in Layered Ferrielectric Materials: Implications for Nanoelectronics

Topological defects in materials present unique opportunities for nanoelectronics, as they allow us to harness new functionalities unavailable in the pristine bulk. However, their study in layered and 2D materials has traditionally been limited to grain boundaries and dislocations present in individual layers. A promising layered metal thiophosphate system, CuInP2S6 (CIPS), exhibits a wide range of functionalities, including ferrielectricity, that are strongly affected by its layered nature and the existence of the van der Waals gap. Here, we explore the landscape of nanoscale topological and point defects affecting layer stacking via high-resolution scanning transmission electron microscopy in cross-sectional form. We show the presence of topological defects, such as edge dislocations, where an additional CIPS layer is inserted and abruptly terminates, as well as domain walls and kinks with high areal density. We find evidence for nanodomains that span multiple layers and observe that the presence of the defects is weakly correlated with the presence of domain boundaries. These studies confirm the rich nature of defect structures in layered materials and suggest opportunities for novel device architectures beyond the single-layer electronics paradigm.