  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.
