Deep-Subwavelength Conversion of Localized Excitons to Trions in 2D Semiconductor Heterostructures Observed by Cathodoluminescence Nanoscopy

Localized excitons in 2D semiconductors are pivotal for advancements in quantum information science. Despite their importance, conventional optical excitation methods, bounded by diffraction limits, inadequately investigate exciton states at the deep-subwavelength scale. In this work, we employ the cathodoluminescence (CL) technique, known as electron beam excitation with spatial resolution that far exceeds the diffraction limit of light, to uncover the localized excitons in h-BN/WS₂/h-BN heterostructures, facilitating a deep-subwavelength conversion of two distinct excitonic states and amplifying the excitonic emission intensity by a factor of 11 within plasmonic hybrid configurations. These enhancements and precise excitations yield a detailed imaging of the transformation from localized excitons to trions at the nanometer scale. Based on density functional theory (DFT) and the finite-element method (FEM), we identify a funneling effect prompted by localized alterations in the valence and conduction bands of WS₂ as the mechanism behind the exciton-state transformations. The findings address major challenges in near-field imaging and transformation of localized excitonic states, enhancing methodologies for probing excitonic behaviors in confined geometries. This advancement enables potential applications in the development of deep-subwavelength excitonic lasers, optoelectronic circuits, and next-generation quantum information technologies.