  We report on a laser annealing procedure which greatly improves the quality
of suspended monolayers of chemical vapor deposition (CVD) grown MoSe2.
Annealing with a green laser locally heats the suspended flake to approximately
600 K, which both removes contaminants and reduces strain gradients. At 4 K, we
observe linewidths as narrow as 3.5 meV (1.6nm) full-width at half-max (FWHM)
for both photoluminescence (PL) and reflection. Large peak reflectances up to
47% are also observed. These values are comparable to those of the highest
quality hexagonal boron nitride (hBN) encapsulated samples. We demonstrate that
this laser annealing process can yield highly spatially homogeneous samples,
with the length scale of the homogeneity limited primarily by the size of the
suspended area. Annealed regions are very stable, exhibiting negligible
deterioration over 24 hours at cryogenic temperatures. The annealing method is
also very repeatable, with substantial improvements of sample quality on every
spot (> 40) tested.
