In Situ Monitoring of the Thermal-Annealing Effect in a Monolayer of MoS 2

The special electronic properties of a two-dimensional material are sensitive to its environment. Thermal annealing (on the path to making a device, say) can change not only the monolayer itself, but also its bonding to the substrate---yet what actually goes on during this process is rarely known. The authors continuously monitor $i\phantom{\rule{0}{0ex}}n$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ the changes in the optical properties of monolayer MoS${}_{2}$ on SiO${}_{2}$ during consecutive thermal cycles, revealing structural evolutions at different stages, as well as the spatial inhomogeneity of the material in response to annealing.