Nanoscale Mapping and Defect-Assisted Manipulation of Surface Plasmon Resonances in 2D Bi₂Te₃/Sb₂Te₃ In-Plane Heterostructures

The Bi₂Te₃/Sb₂Te₃ in-plane heterostructure is reported as a low-dimensional tunable chalcogenide well suited as plasmonic building block for the visible−UV spectral range. Electron-driven plasmon excitations of low-dimensional Bi₂Te₃/Sb₂Te₃ are investigated by monochromated electron energy loss spectroscopy spectrum imaging. To resolve the nanoscale spatial distribution of various local plasmonic resonances, singular value decomposition is used to disentangle the spectral data and identify the individual spectral contributions of various corner, edge, and face modes. Furthermore, defect-plasmon interactions are investigated both for nanoscale intrinsic and thermally induced extrinsic polygonal defects (in situ sublimation). Signature of defect-induced red shift ranging from a several hundreds of millielectronvolts to a few electronvolts, broadening of various plasmon response, together with selective enhancement and significant variations in their intensity are detected. This study highlights the presence of a heterointerface and identifies defects as physical tuning pathways to modulate the plasmonic response over a broad spectral range. Finally, the experimental observations are compared qualitatively and validated with numerical simulations using the electron-driven discrete dipole approximation. Low-dimensional Bi₂Te₃/Sb₂Te₃ as a less explored plasmonic system holds great promises as emerging platform for integrated plasmonics. Furthermore, introducing controlled structural defects can open the door for nanoengineering of plasmonic properties in such systems.