Thermal Annealing Effects on Naturally Contacted Monolayer MoS₂

We study the effects of postgrowth processing including thermal annealing and laser annealing on the quality, crystallinity, and optical properties of monolayer molybdenum di-sulfide (MoS₂) which is grown using a novel chemical vapor deposition (CVD) method. In this CVD process a thin layer of metal oxide which is formed on bulk lithographically defined molybdenum patterns serves as the nucleation precursor. The preliminary photoluminescence (PL) measurements on monolayer MoS₂ have shown a blueshift in the lower energy peak after annealing. In addition, the PL map became more uniform up to an annealing temperature of 300°C. At higher temperatures, isolated monolayers begin to crack along the grain boundaries, which leads to variations in luminescence. We also performed an optical investigation of thermal annealing effects on monolayer MoS₂ anchored to the molybdenum patterns via PL measurements. Our observation showed that after an annealing temperature of 200°C, the anchored materials became susceptible to laser ablation. This observation inspired us to further study possible laser processing for localized thermal treatment of the materials.