Fast growth of large-grain and continuous MoS2 films through a self-capping vapor-liquid-solid method

Most chemical vapor deposition methods for transition metal dichalcogenides use an extremely small amount of precursor to render large single-crystal flakes, which usually causes low coverage of the materials on the substrate. In this study, a self-capping vapor-liquid-solid reaction is proposed to fabricate large-grain, continuous MoS₂ films. An intermediate liquid phase-Na₂Mo₂O₇ is formed through a eutectic reaction of MoO₃ and NaF, followed by being sulfurized into MoS₂. The as-formed MoS₂ seeds function as a capping layer that reduces the nucleation density and promotes lateral growth. By tuning the driving force of the reaction, large mono/bilayer (1.1 mm/200 μm) flakes or full-coverage films (with a record-high average grain size of 450 μm) can be grown on centimeter-scale substrates. The field-effect transistors fabricated from the full-coverage films show high mobility (33 and 49 cm² V^-1 s^-1 for the mono and bilayer regions) and on/off ratio (1 ~ 5 × 10⁸) across a 1.5 cm × 1.5 cm region.