Formation of nanosized monolayer MoS₂ by oxygen-assisted thinning of multilayer MoS₂

We report the controllable nanosized local thinning of multi-layer (2 L and 3 L)-thickness MoS₂ films down to the monolayer (1 L) thickness using the simple method of annealing in a dry oxygen atmosphere. The annealing temperature was optimized in the range of 240 °C to 270 °C for 1.5 h, and 1 L thick nanosized pits were developed on the uniform film of the 2 L and 3 L MoS₂ grown using the chemical vapor deposition method. We characterized the formation of the 1 L nanosized pits using nanoscale confocal photoluminescence (PL) and Raman spectroscopy. We observed that the PL intensity increased and the Raman frequency shifted, representative of the characteristics of 1 L MoS₂ films. A subsequent hydrogen treatment process was useful for removing the oxygen-induced doping effect resulting from the annealing.