Nanoscale modification of WS$_2$ trion emission by its local electromagnetic environment

TL;DR

This study uses nanometer-resolved electron spectroscopy to directly correlate local structural and chemical modifications in WS$_2$ monolayers with their optical emission properties, revealing how nanoscale dielectric patches and charge accumulation influence trion emission.

Contribution

It introduces a method combining electron energy loss spectroscopy and cathodoluminescence to spatially correlate optical responses with nanoscale structural and chemical features in transition metal dichalcogenide monolayers.

Findings

Local dielectric patches modulate trion emission but not exciton emission.

Charge accumulation regions enhance trion emission.

Point defects may be involved in localized exciton formation.

Abstract

Structural, electronic, and chemical nanoscale modifications of transition metal dichalcogenide monolayers alter their optical properties, including the generation of single photon emitters. A key missing element for complete control is a direct spatial correlation of optical response to nanoscale modifications, due to the large gap in spatial resolution between optical spectroscopy and nanometer resolved techniques, such as transmission electron microscopy or scanning tunneling microscopy. Here, we bridge this gap by obtaining nanometer resolved optical properties using electron spectroscopy, specifically electron energy loss spectroscopy (EELS) for absorption and cathodoluminescence (CL) for emission, which were directly correlated to chemical and structural information. In an h-BN/WS$_2$/h-BN heterostructure, we observe local modulation of the trion (X$^{-}$) emission due to tens of nanometer wide dielectric patches, while the exciton, X$_A$, does not follow the same modulation. Trion emission also increases in regions where charge accumulation occurs, close to the carbon film supporting the heterostructures. Finally, localized exciton emission (L) detection is not correlated to strain variations above 1 $\%$, suggesting point defects might be involved in their formations.