A highly sensitive chemical gas detecting transistor based on highly crystalline CVD-grown MoSe<Subscript>2</Subscript> films

Layered semiconductors with atomic thicknesses are becoming increasingly important as active elements in high-performance electronic devices owing to their high carrier mobilities,large surface-to-volume ratios,and rapid electrical responses to their surrounding environments.Here,we report the first implementation of a highly sensitive chemical-vapor-deposition-grown multilayer MoSe2 field-effect transistor (FET) in a NO2 gas sensor.This sensor exhibited ultra-high sensitivity (S =ca.1,907 for NO2 at 300 ppm),real-time response,and rapid on-off switching.The high sensitivity of our MoSe2 gas sensor is attributed to changes in the gap states near the valence band induced by the NO2 gas absorbed in the MoSe2,which leads to a significant increase in hole current in the off-state regime.Device modeling and quantum transport simulations revealed that the variation of gap states with NO2 concentration is the key mechanism in a MoSe2 FET-based NO2 gas sensor.This comprehensive study,which addresses material growth,device fabrication,characterization,and device simulations,not only indicates the utility of MoSe2 FETs for high-performance chemical sensors,but also establishes a fundamental understanding of how surface chemistry influences carrier transport in layered semiconductor devices.     

A Colorimetric Multifunctional Sensing Method for Structural‐Durability‐Health Monitoring Systems

A colorimetric multifunctional phototransmittance‐based structural durability monitoring system is developed. The system consists of an array with four indium gallium zinc oxide (IGZO)‐based phototransistors, a light source at a wavelength of 405 nm through a side‐emitting optical fiber, and pH‐ and Cl‐selective color‐variable membranes. Under illumination at the wavelength of 405 nm at corrosion status, the pH‐ and Cl‐responsive membrane, showing a change in their color, generates a change in the intensity of the transmitted light, which is received by the phototransistor array in the form of an electrical current. I_ds and R (I_ds/I_{pH 12}) are inversely proportional to the pH, which ranges from 10 to 12. When the pH drops from 12 to 10, the magnitude of I_ds and R increases to ≈10³. In the case of Cl detection, I_ds and R (I_ds/I_{Cl 0 wt%}) increase nearly 50 times with an increase in Cl concentration of 0.05 wt%, and when the Cl concentration reaches 0.30 wt%, I_ds and R increase to ≈10³ times greater. This multifunctional colorimetric durability sensing system demonstrates considerable potential as a novel smart‐diagnostic tool of structural durability with high stability, high sensitivity, and multifunction.