Reductive exfoliation of substoichiometric MoS2 bilayers using hydrazine salts

Abstract

Substoichiometric molybdenum disulphide (MoS_x) nanosheets are successfully synthesised following a novel reductive route using hydrazine salts. The resulting two dimensional crystals are found to be highly monodispersed in thickness, forming exclusively 1.9 ± 0.2 nm thick bilayers. The lateral dimensions of the nanosheets are governed by the precursor bulk particle's size. Exploring a range of hydrazine derivatives with various degrees of steric hindrance leads to the conclusion that intercalation does not occur during the process and that exfoliation is instead facilitated by the reduction of Mo centres leading to the exfoliation of substoichiometric bilayers with distorted lattices. The lattice distortion is found to be persistent across all samples with XPS analysis pointing towards a S to Mo ratio of 1.2. The resulting material features an electronic bandgap of 2.1 eV, which is wider than that of pristine monolayer MoS₂ with relatively longer radiative decay time.