Layer Thinning and Etching of Mechanically Exfoliated MoS 2 Nanosheets by Thermal Annealing in Air

A simple thermal annealing method for layer thinning and etching of mechanically exfoliated MoS 2 nanosheets in air is reported. Using this method, single‐layer (1L) MoS 2 nanosheets are achieved after the thinning of MoS 2 nanosheets from double‐layer (2L) to quadri‐layer (4L) at 330 °C. The as‐prepared 1L MoS 2 nanosheet shows comparable optical and electrical properties with the mechanically exfoliated, pristine one. In addition, for the first time, the MoS 2 mesh with high‐density of triangular pits is also fabricated at 330 °C, which might arise from the anisotropic etching of the active MoS 2 edge sites. As a result of thermal annealing in air, the thinning of MoS 2 nanosheet is possible due to its oxidation to form MoO 3 . Importantly, the MoO 3 fragments on the top of thinned MoS 2 layer induces the hole injection, resulting in the p ‐type channel in fabricated field‐effect transistors.