Core/Shell Quantum Dot-Like Excitonic Emissions of Strain-Localized Emitters at Atomically Thin Semiconductor-Metal Interface

Scanning probe techniques have significantly advanced our understanding of the electronic and optical properties of nanoscale materials, including organic single molecules and inorganic low-dimensional nanomaterials such as quantum dots, nanowires, and two-dimensional semiconductors. These methods enable the exploration of localized emitters confined to nanoscale areas, which are crucial for highly efficient optoelectronics and quantum information technologies. Among various nanoscale emitters, strain-localized excitons in transition metal dichalcogenides have shown potential as single-photon sources, yet the impact of charge transfer on excitonic emission is not fully understood.<br/>Here, we report distinct excitonic emission behaviors of strain-localized emitters in monolayer WSe₂ on different types of semiconductor-metal junctions, i.e. Schottky and Ohmic interfaces, achieved by varying the annealing temperature. In Schottky interfaces, we observe two excitonic emissions: one at the core (1.45 eV) and another at the shell (1.57 eV) of the nanobubble, which are distinct from the neutral exciton of WSe₂ (1.63 eV). Using techniques such as tip-enhanced photoluminescence, Kelvin probe force microscopy, piezoelectric force microscopy, and Föppl–von Kármán calculations, we attribute the core and shell emissions to the piezoelectric potential due to the strong polarity of the Schottky interface and the localized strain field, respectively. Conversely, nanobubbles on Ohmic contacts show only strain-localized excitons (1.56 eV), indicating that the strong polarity of the interface plays a crucial role in forming core/shell-like emissions.<br/>Our approach offers reliable and electronically controllable core/shell-like excitonic emitters from two-dimensional materials for future applications in nano and quantum photonics.