  The role of defects in two-dimensional semiconductors and how they affect the
intrinsic properties of these materials have been a wide researched topic over
the past decades. Optical characterization such as photoluminescence and Raman
spectroscopies are important tools to probe their physical properties and the
impact of defects. However, conventional optical techniques present a spatial
resolution limitation lying in a $\mu$m-scale, which can be overcomed by the
use of near-field optical measurements. Here, we use tip-enhanced
photoluminescence and Raman spectroscopies to unveil nanoscale optical
heterogeneities at grain boundaries, local strain fields and edges in grown
MoS$_{2}$ monolayers. A noticeable enhancement of the exciton peak intensity
corresponding to a trion emission quenching is observed at narrow regions down
to 47 nm of width at grain boundaries related to doping effects. Besides,
localized strain fields inside the sample lead to non-uniformities in the
intensity and energy position of photoluminescence peaks. Finally, distinct
samples present different nano-optical responses at their edges due to strain
and passivation defects. The passivated defective edges show a
photoluminescence intensity enhancement and energy blueshift as well as a
frequency blueshift of the 2LA Raman mode. On the other hand, the strained
edges display a photoluminescence energy redshift and frequency redshifts for
E$_{2g}$ and 2LA Raman modes. Our work shows that different defect features can
be only probed by using optical spectroscopies with a nanometric resolution,
thus revealing hindered local impact of different nanoscale defects in
two-dimensional materials.
