Synthesis of Atomically Thin Transition Metal Ditelluride Films by Rapid Chemical Transformation in Solution Phase

The controlled synthesis of large-area, atomically thin molybdenum and tungsten ditelluride (MoTe₂ and WTe₂) crystals is crucial for their emerging applications based on the attractive electronic properties. However, the solution phase synthesis of high-quality and large-area MoTe₂ or WTe₂ ultrathin films have not been achieved yet. In this study, we synthesized for the first time, large-area atomically thin MoTe₂ and WTe₂ films in solution phase, through rapid crystal formation directly on a conducting substrate. For the synthesis, we developed a new Te precursor. The crystal growth involves an in situ chemical transformation from Te nanoparticles into MoTe₂ or WTe₂ thin films. The synthesis enables precise control of the number of atomic layers over a large area, from a monolayer to multilayers. Micropatterned MoTe₂ thin films are also readily synthesized in situ using the same process. The photodetector made of 3-layer semiconducting MoTe₂ thin films exhibits high photoresponsivity (R_λ) over a broad spectral range (300-1100 nm) with a maximum in the near-IR region, including a R_λ = 30 mA W^-1 even at λ = 1.10 μm and a fast photoresponse (87 μs). Our synthesis method presents a crucial step in the solution phase synthesis of metal telluride ultrathin films and paves the way for their large-scale emerging applications.