Highly Flexible MoS₂ Thin-Film Transistors with Ion Gel Dielectrics

Molybdenum disulfide (MoS₂) thin-film transistors were fabricated with ion gel gate dielectrics. These thin-film transistors exhibited excellent band transport with a low threshold voltage (<1 V), high mobility (12.5 cm²/(V·s)) and a high on/off current ratio (10⁵). Furthermore, the MoS₂ transistors exhibited remarkably high mechanical flexibility, and no degradation in the electrical characteristics was observed when they were significantly bent to a curvature radius of 0.75 mm. The superior electrical performance and excellent pliability of MoS₂ films make them suitable for use in large-area flexible electronics

Large-Area Synthesis of Highly Crystalline WSe₂ Monolayers and Device Applications

The monolayer transition metal dichalcogenides have recently attracted much attention owing to their potential in valleytronics, flexible and low-power electronics, and optoelectronic devices. Recent reports have demonstrated the growth of large-size two-dimensional MoS₂ layers by the sulfurization of molybdenum oxides. However, the growth of a transition metal selenide monolayer has still been a challenge. Here we report that the introduction of hydrogen in the reaction chamber helps to activate the selenization of WO₃, where large-size WSe₂ monolayer flakes or thin films can be successfully grown. The top-gated field-effect transistors based on WSe₂ monolayers using ionic gels as the dielectrics exhibit ambipolar characteristics, where the hole and electron mobility values are up to 90 and 7 cm²/Vs, respectively. These films can be transferred onto arbitrary substrates, which may inspire research efforts to explore their properties and applications. The resistor-loaded inverter based on a WSe₂ film, with a gain of ∼13, further demonstrates its applicability for logic-circuit integrations

Monolayer MoSe₂ Grown by Chemical Vapor Deposition for Fast Photodetection

Monolayer molybdenum disulfide (MoS₂) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS₂ devices. Here, highly crystalline molybdenum diselenide (MoSe₂) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS₂ and MoSe₂ monolayers reveals that the MoSe₂ monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe₂ presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS₂ monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS₂. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe₂ and MoS₂ and is useful for guiding future designs in 2D material-based optoelectronic devices