Synthesis of large-area patterned MoS 2 is considered the principle base for realizing high-performance MoS 2 -based flexible electronic devices. Patterning and transferring MoS 2 films to target flexible substrates, however, require conventional multi-step photolithography patterning and transferring process, despite tremendous progress in the facilitation of practical applications. Herein, an approach to directly synthesize large-scale MoS 2 patterns that combines inkjet printing and thermal annealing is reported. An optimal precursor ink is prepared that can deposit arbitrary patterns on polyimide films. By introducing a gas atmosphere of argon/hydrogen (Ar/H 2 ), thermal treatment at 350 °C enables an in situ decomposition and crystallization in the patterned precursors and, consequently, results in the formation of MoS 2 . Without complicated processes, patterned MoS 2 is obtained directly on polymer substrate, exhibiting superior mechanical flexibility and durability (≈2% variation in resistance over 10,000 bending cycles), as well as excellent chemical stability, which is attributed to the generated continuous and thin microstructures, as well as their strong adhesion with the substrate. As a step further, this approach is employed to manufacture various flexible sensing devices that are insensitive to body motions and moisture, including temperature sensors and biopotential sensing systems for real-time, continuously monitoring skin temperature, electrocardiography, and electromyography signals.

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A facile approach for surface defect engineering based on high-energy electron irradiation is proposed here to produce a graphene/polymer composite flexible humidity sensor with high humidity resistance and responsiveness. The responsiveness of the graphene/polymer composite humidity sensor following electron irradiation was ∼22.4-fold greater than the unirradiated humidity sensor. When the relative humidity was 97.3%, the responsiveness of the sensor was 1.2 × 105. In addition, the irradiated humidity sensor maintained an excellent response after 10 water resistance tests. Furthermore, material characterization techniques demonstrated that graphene/polymer composite materials with low crosslinking density could be produced by electron irradiation at the appropriate fluence. Concurrently, the specific surface area of the graphene/polymer composite material was increased, and several oxygen-containing functional groups were generated, providing more active sites for water molecules to enhance the stability and responsiveness of the sensor. Thus, the irradiated graphene/polymer composite humidity sensor has potential applications in human respiratory monitoring and noncontact switching. Moreover, the surface defect engineering of electron irradiation provides a facile strategy for obtaining graphene/polymer composite flexible humidity sensors with high comprehensive properties.