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 cm(2)/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.

Molybdenum disulfide (MoS(2)) 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 cm(2)/(V·s)) and a high on/off current ratio (10(5)). Furthermore, the MoS(2) 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 MoS(2) films make them suitable for use in large-area flexible electronics.

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

Complementary inverters constructed from large-area monolayers of WSe2 and MoS2 achieve excellent logic swings and yield an extremely high gain, large total noise margin, low power consumption, and good switching speed. Moreover, the WSe2 complementary-like inverters built on plastic substrates exhibit high mechanical stability. The results provide a path toward large-area flexible electronics.

Ambipolar electric double-layer transistors (EDLTs) using organic single crystals and ion-gel electrolytes are successfully created by optimising the fabrication of gel films. The p- and n-type EDLTs enable us to investigate the HOMO-LUMO gap energy of semiconductors, offering a new method with which to measure it.