Recent Advances in Chemoresistive Gas Sensors Using Two-Dimensional Materials.

Two-dimensional (2D) materials have emerged as a promising candidate in the chemoresistive gas sensor field to overcome the disadvantages of conventional metal-oxide semiconductors owing to their strong surface activities and high surface-to-volume ratio. This review summarizes the various approaches to enhance the 2D-material-based gas sensors and provides an overview of their progress. The distinctive attributes of semiconductor gas sensors employing 2D materials will be highlighted with their inherent advantages and associated challenges. The general operating principles of semiconductor gas sensors and the unique characteristics of 2D materials in gas-sensing mechanisms will be explored. The pros and cons of 2D materials in gas-sensing channels are discussed, and a route to overcome the current challenges will be delivered. Finally, the recent advancements to enhance the performance of 2D-material-based gas sensors including photo-activation, heteroatom doping, defect engineering, heterostructures, and nanostructures will be discussed. This review should offer a broad range of readers a new perspective toward the future development of 2D-material-based gas sensors.

Boosting the Optoelectronic Properties of Molybdenum Diselenide by Combining Phase Transition Engineering with Organic Cationic Dye Doping.

Two-dimensional layered transition metal dichalcogenides (TMDs) have been investigated intensively as next-generation semiconducting materials. However, conventional TMD-based devices exhibit large contact resistance at the interface between the TMD and the metal electrode because of Fermi level pinning and the Schottky barrier, which results in poor charge injection. Here, we present enhanced charge transport characteristics in molybdenum diselenide (MoSe2) by means of a sequential engineering process called PESOD-2H/1T (i.e., phase transition engineering combined with surface transfer organic cationic dye doping; 2H and 1T represent the trigonal prismatic and octahedral phases, respectively). Substantial improvements are observed in PESOD-processed MoSe2 phototransistors, specifically, an approximately 40 000-fold increase in effective carrier mobility and a 100 000-fold increase in photoresponsivity, compared with the mobility and photoresponsivity of intact MoSe2 phototransistors. Moreover, the PESOD-processed MoSe2 phototransistor on a flexible substrate maintains its optoelectronic properties under tensile stress, with a bending radius of 5 mm.