ABSTRACT
Molybdenum disulfide (MoS2) is a representative transition metal sulfide that is widely used in gas and biological detection, energy storage, and integrated electronic devices due to its unique optoelectrical and chemical characteristics. To advance toward the miniaturization and on-chip integration of functional devices, it is strategically important to develop a high-precision and cost-effective method for the synthesis and integration of MoS2 patterns and functional devices. Traditional methods require multiple steps and time-consuming processes such as material synthesis, transfer, and photolithography to fabricate MoS2 patterns at the desired region on the substrate, significantly increasing the difficulty of manufacturing micro/nanodevices. In this work, we propose a single-step femtosecond laser-induced photochemical method which can realize the fabrication of arbitrary two-dimensional edge-unsaturated MoS2 patterns with high efficiency in microscale. Based on this method, MoS2 can be synthesized at a rate of 150 µm/s, 2 orders of magnitude faster than existing laser-based thermal decomposition methods without sacrificing the resolution and quality. The morphology and roughness of the MoS2 pattern can be controlled by adjusting the laser parameters. Furthermore, the femtosecond laser direct writing (FLDW) method was used to fabricate microscale MoS2-based gas detectors that can detect a variety of toxic gases with high sensitivity up to 0.5 ppm at room temperature. This FLDW method is not only applicable to the fabrication of high-precision MoS2 patterns and integrated functional devices, it also provides an effective route for the development of other micro/nanodevices based on a broad range of transition metal sulfides and other functional materials.
ABSTRACT
The widespread use of stimuli-responsive hydrogels is closely related to their synthesis efficiency. However, the widely used thermal-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels usually require a time-consuming synthesis process to produce (more than 12 h) and exhibit a relatively slow response speed in the field of cryo-polymerization. In this study, a sequence of thawing polymerization after freezing polymerization by a two-step method of free radical polymerization for the efficient synthesis of PNIPAM hydrogels (merely 2 h) with an excellent comprehensive performance is demonstrated. Results show that the overall performance of the as-synthesized PNIPAM hydrogels is at the top level among reported works despite the significantly reduced preparation time. Moreover, after incorporating multi-walled carbon nanotubes (MWNTs), the PNIPAM hydrogels exhibit a rapid near-infrared (NIR) light-response and programmable shape-morphing capability. It is believed that such a viable and time-saving synthetic method for producing PNIPAM hydrogels of high performance will lay a solid foundation for drug delivery and smart actuators.
