MoS 2 nanosheets via electrochemical lithium-ion intercalation under ambient conditions

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are continuously attracting attention for both fundamental studies and technological applications. The physical and chemical properties of ultrathin TMD sheets are extraordinarily different from those of the corresponding bulk materials and for this reason their production is a stimulating topic, especially when the preparation method enables to obtain a remarkable yield of nanosheets with large area and high quality. Herein, we present a fast (<1 h) electrochemical exfoliation of molybdenum disulfide (MoS 2 ) via lithium-ion intercalation, by using a solution of lithium chloride in dimethyl sulfoxide (DMSO). Unlike the conventional intercalation methods based on dangerous organolithium compounds, our approach leads to the possibility to obtain mono-, bi- and tri-layer thick MoS 2 nanosheets with a large fraction of the semiconducting 2H phase (∼60%), as estimated by X-ray photoelectron spectroscopy (XPS). The electrical properties of the exfoliated material were investigated through the fabrication and characterization of back-gated field-effect transistors (FETs) based on individual MoS 2 nanosheets. As-fabricated devices displayed unipolar semiconducting behavior (n-type) with field-effect mobility µ FE ≤ 10 −3 cm 2 V −1 s −1 and switching ratio I on /I off ≤ 10, likely limited by 1T/2H polymorphism and defects (e.g. sulfur vacancies) induced during the intercalation/exfoliation process. A significant enhancement of the electrical performances could be achieved through a combination of vacuum annealing (150 °C) and sulfur-vacancy healing with vapors of short-chain alkanethiols, resulting in µ FE up to 2 × 10 −2 cm 2 V −1 s −1 and I on /I off ≈ 100. Our results pave the way towards the fast preparation – under ambient conditions – of semiconducting MoS 2 nanosheets, suitable for application in low cost (opto-)electronic devices.