Wet chemical thinning of molybdenum disulfide down to its monolayer

We report on the preparation of mono- and bi-layer molybdenum disulfide (MoS2) from a bulk crystal by facile wet chemical etching. We show that concentrated nitric acid (HNO3) effectively etches thin MoS2 crystals from their edges via formation of MoO3. Interestingly, etching of thin crystals on a substrate leaves behind unreacted mono- and bilayer sheets. The flakes obtained by chemical etching exhibit electronic quality comparable to that of mechanically exfoliated counterparts. Our findings indicate that the self-limiting chemical etching is a promising top-down route to preparing atomically thin crystals from bulk layer compounds.