  The optical properties of transition metal dichalcogenides have previously
been modified at the nanoscale by using mechanical and electrical
nanostructuring. However, a clear experimental picture relating the local
electronic structure with emission properties in such structures has so far
been lacking. Here, we use a combination of scanning tunneling microscopy (STM)
and near-field photoluminescence (nano-PL) to probe the electronic and optical
properties of single nano-bubbles in bilayer heterostructures of WSe2 on MoSe2.
We show from tunneling spectroscopy that there are electronic states deeply
localized in the gap at the edge of such bubbles, which are independent of the
presence of chemical defects in the layers. We also show a significant change
in the local bandgap on the bubble, with a continuous evolution to the edge of
the bubble over a length scale of ~20 nm. Nano-PL measurements observe a
continuous redshift of the interlayer exciton on entering the bubble, in
agreement with the band to band transitions measured by STM. We use
self-consistent Schr\"odinger-Poisson (SP) simulations to capture the essence
of the experimental results and find that strong doping in the bubble region is
a key ingredient to achieving the observed localized states, together with
mechanical strain.
