Surfactant-free nanoflakes of n-type Bi2 Te3 and Bi2 Se3 are synthesized in high yields. Their suspensions are mixed to create nanocomposites with heterostructured nanograins. A maximum ZT (0.7 at 400 K) is achieved with a broad content of 10-15% Bi2 Se3 in the nanocomposites.

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Ultrathin transition metal dichalcogenides (TMDs) have exotic electronic properties. With success in easy synthesis of high quality TMD thin films, the potential applications will become more viable in electronics, optics, energy storage, and catalysis. Synthesis of TMD thin films has been mostly performed in vacuum or by thermolysis. So far, there is no solution phase synthesis to produce large-area thin films directly on target substrates. Here, this paper reports a one-step quick synthesis (within 45-90 s) of TMD thin films (MoS , WS , MoSe , WSe , etc.) on solid substrates by using microwave irradiation on a precursor-containing electrolyte solution. The numbers of the quintuple layers of the TMD thin films are precisely controllable by varying the precursor's concentration in the electrolyte solution. A photodetector made of MoS thin film comprising of small size grains shows near-IR absorption, supported by the first principle calculation, exhibits a high photoresponsivity (>300 mA W ) and a fast response (124 µs). This study paves a robust way for the synthesis of various TMD thin films in solution phases.

2D metal chalcogenide thin films have recently attracted considerable attention owing to their unique physicochemical properties and great potential in a variety of applications. Synthesis of large-area 2D metal chalcogenide thin films in controllable ways remains a key challenge in this research field. Recently, the solution-based synthesis of 2D metal chalcogenide thin films has emerged as an alternative approach to vacuum-based synthesis because it is relatively simple and easy to scale up for high-throughput production. In addition, solution-based thin films open new opportunities that cannot be achieved from vacuum-based thin films. Here, a comprehensive summary regarding the basic structures and properties of different types of 2D metal chalcogenides, the mechanistic details of the chemical reactions in the synthesis of the metal chalcogenide thin films, recent successes in the synthesis by different reaction approaches, and the applications and potential uses is provided. In the last perspective section, the technical challenges to be overcome and the future research directions in the solution-based synthesis of 2D metal chalcogenides are discussed.

The controlled synthesis of large-area, atomically thin molybdenum and tungsten ditelluride (MoTe 2 and WTe 2 ) crystals is crucial for their emerging applications based on the attractive electronic properties. However, the solution phase synthesis of high-quality and large-area MoTe 2 or WTe 2 ultrathin films have not been achieved yet. In this study, we synthesized for the first time, large-area atomically thin MoTe 2 and WTe 2 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 MoTe 2 or WTe 2 thin films. The synthesis enables precise control of the number of atomic layers over a large area, from a monolayer to multilayers. Micropatterned MoTe 2 thin films are also readily synthesized in situ using the same process. The photodetector made of 3-layer semiconducting MoTe 2 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.