# Exciton mapping at subwavelength scales in two-dimensional materials

## TL;DR

This study uses spatially resolved EELS with a monochromated electron source to map excitons at nanometer scales in 2D MoS2/MoSe2 interfaces, revealing local variations linked to composition and interface roughness.

## Contribution

It demonstrates nanometer-scale exciton mapping in 2D materials using advanced EELS techniques, achieving resolution much smaller than the photon wavelength.

## Key findings

- Exciton maps show variations at 10 nm separation.
- Excitonic signatures follow chemical composition.
- No exciton peak shift observed across interfaces.

## Abstract

Spatially resolved EELS has been performed at diffuse interfaces between MoS$_2$ and MoSe$_2$ single layers. With a monochromated electron source (20 meV) we have successfully probed excitons near the interface by obtaining the low loss spectra at the nanometer scale. The exciton maps clearly show variations even with a 10 nm separation between measurements; consequently the optical bandgap can be measured with nanometer-scale resolution, which is 50 times smaller than the wavelength of the emitted photons. By performing core-loss EELS at the same regions, we observe that variations in the excitonic signature follow the chemical composition. The exciton peaks are observed to be broader at interfaces and heterogeneous regions, possibly due to interface roughness and alloying effects. Moreover, we do not observe shifts of the exciton peak across the interface, possibly because the interface width is not much larger than the exciton Bohr radius.