Abstract
Abstract Two-dimensional (2D) transition metal dichalcogenides (TMDCs), possessing unique exciton luminescence properties, have attracted significant attention for use in optical and electrical devices. TMDCs are also high refractive index materials that can strongly confine the electromagnetic field in nanoscale dimensions when patterned into nanostructures, thus resulting in complex light emission that includes exciton and dielectric resonances. Here, we use cathodoluminescence (CL) to experimentally visualize the emission modes of single molybdenum disulfide (MoS2) nanoflakes and to investigate luminescence enhancement due to dielectric resonances in nanoscale dimensions, by using a scanning transmission electron microscope. Specifically, we identify dielectric modes whose resonant wavelength is sensitive to the shape and size of the nanoflake, and exciton emission peaks whose energies are insensitive to the geometry of the flakes. Using a four-dimensional CL method and boundary element method simulations, we further theoretically and experimentally visualize the emission polarization and angular emission patterns, revealing the coupling of the exciton and dielectric resonant modes. Such nanoscopic observation provides a detailed understanding of the optical responses of MoS2 including modal couplings of excitons and dielectric resonances which play a crucial role in the development of energy conversion devices, single-photon emitters, and nanophotonic circuits with enhanced light-matter interactions.
Highlights
Molybdenum disulfide (MoS2), one of the most common materials amongst two-dimensional (2D) transition metal dichalcogenides (TMDCs) [1, 2], has received significant attention owing to its semiconductive nature, tunable bandgap, and its strong light-absorption capacity in the visible region
We have individually visualized the dielectric resonance and exciton emission modes in isolated MoS2 nanoflakes by spectral deconvolution of data obtained with the CLSTEM technique
The energy and number of dielectric resonance modes of MoS2 flakes depend on the flake shape and size, and their emission is dominated by the excitation at the corner and the edge of the structures, where the dielectric field hotspots are located
Summary
Molybdenum disulfide (MoS2), one of the most common materials amongst two-dimensional (2D) transition metal dichalcogenides (TMDCs) [1, 2], has received significant attention owing to its semiconductive nature, tunable bandgap, and its strong light-absorption capacity in the visible region. These properties enable its implementation in the production of semiconductor sensors [3], photocatalytic [4], hydrothermal and optoelectronic devices [2]. To probe and understand the origin of the sub-wavelength optical properties of the MoS2 nanostructures, visualization of the optical properties beyond the diffraction limit of light is required, This work is licensed under the Creative Commons Attribution 4.0
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