  We perform in-situ two-cycle thermal cycling and annealing studies for a
transferred CVD-grown monolayer MoS2 on a SiO2/Si substrate, using spatially
resolved micro-Raman and PL spectroscopy. After the thermal cycling and being
annealed at 305 deg C twice, the film morphology and film-substrate bonding are
significantly modified, which together with the removal of polymer residues
cause major changes in the strain and doping distribution over the film, and
thus the optical properties. Before annealing, the strain associated with
ripples in the transferred film dominates the spatial distributions of the PL
peak position and intensity over the film; after annealing, the variation in
film-substrate bonding, affecting both strain and doping, becomes the leading
factor. This work reveals that the film-substrate bonding, and thus the strain
and doping, is unstable under thermal stress, which is important for
understanding the substrate effects on the optical and transport properties of
the 2D material and their impact on device applications.
