Geometry-Controlled Exciton Selectivity in Monolayer MoS2 Using Plasmonic Hollow Nanocavities

TL;DR

This study demonstrates how hollow plasmonic nanocavities can be geometrically tuned to selectively enhance and control excitonic emission in monolayer MoS2, advancing nanoscale optoelectronic applications.

Contribution

It introduces a numerical approach to optimize hollow gold nanocavities for exciton-selective emission in monolayer MoS2, achieving significant enhancement and spectral control.

Findings

Excitation rate up to 4.34-fold enhancement.

Radiative decay rate increased by over 40 times.

Exciton peak ratios improved up to 2.4 times.

Abstract

Spectral control of closely spaced excitonic transitions is central to valleytronic photonics, nanoscale light sources, and wavelength-encoded sensing. In monolayer molybdenum disulfide (MoS2), the A and B excitons are separated by only tens of meV, making selective excitonic emission control both fundamentally important and technologically challenging. Here, we numerically investigate plasmon-enhanced excitonic emission from monolayer MoS2 coupled to vertically oriented hollow gold nanocylindrical cavities through a dielectric spacer. Finite-difference time-domain simulations combined with a photoluminescence-rate framework enable separate evaluation of excitation enhancement, radiative decay modification, nonradiative quenching, and excitonic charge generation. By tuning the cavity aspect ratio, the localized surface plasmon resonance is selectively aligned with either the A- or B-exciton transition, while the spacer thickness and refractive index regulate near-field coupling and the local density of optical states. Under optimized conditions, the excitation rate is enhanced by up to 4.34-fold and the radiative decay rate by more than 40-fold, yielding photoluminescence enhancements of 143.85 and 87.27 for the A and B excitons, respectively. The cavity also redistributes the relative excitonic peak intensities, producing exciton-selective peak ratios up to 2.4 times higher than those of bare MoS2. These results establish hollow plasmonic nanocavities as geometry-tunable platforms for exciton-selective emission and charge-generation control in atomically thin semiconductors.