To realize continuously and stably work in a “moist/hot environment”, flexible electronics with excellent humid resistance, anti-swelling, and detection sensitivity are demanding. Herein, a solvent-resistant and temperature-ultrasensitive hydrogel sensor was prepared by combining MXene and quaternized chitosan (QCS) with the binary polymer chain. The strong electrostatic interaction between the QCS chain and the poly(acrylic acid) (PAA) network endows the hydrogel stability against solvent erosion, high temperature, and high humidity. The strong dynamic interaction between MXene and polymer matrix significantly improves the mechanical properties and sensing (strain and temperature) sensitivity of the hydrogel. The hydrogel strain sensor exhibits a high gauge factor (5.53), temperature/humidity tolerance (equilibrium swelling ratio of 2.5% at 80 °C), and excellent cycle stability, which could achieve a remote and accurate perception of complex human motion and environment fluctuation under aquatic conditions. Moreover, the hydrogel sensor exhibits impressive thermal response sensitivity (−3.183%/°C), ultra-short response time (< 2.53 s), and a low detection limit (< 0.5 °C) in a wide temperature range, which is applied as an indicator of the body surface and ambient temperature. In short, this study broadens the application scenarios of hydrogels in persistent extreme thermal and wet environments.

Two-dimensional (2D) transition metal dichalcogenide (TMDC) monolayers, a class of ultrathin materials with a direct bandgap and high exciton binding energies, provide an ideal platform to study the photoluminescence (PL) of light-emitting devices. Atomically thin TMDCs usually contain various defects, which enrich the lattice structure and give rise to many intriguing properties. As the influences of defects can be either detrimental or beneficial, a comprehensive understanding of the internal mechanisms underlying defect behaviour is required for PL tailoring. Herein, recent advances in the defect influences on PL emission are summarized and discussed. Fundamental mechanisms are the focus of this review, such as radiative/nonradiative recombination kinetics and band structure modification. Both challenges and opportunities are present in the field of defect manipulation, and the exploration of mechanisms is expected to facilitate the applications of 2D TMDCs in the future.

Two-dimensional (2D) materials have attracted great attention in optoelectronics because of their unique structure, optical and electrical properties. Designing high-performance photodetectors and implementing their applications are eager to promote the development of 2D materials. Position-sensitive detector (PSD) is an optical inspection device for the precise measurements of position, distance, angle, and other relevant physical variables. It is a widely used component in the fields of tracking, aerospace, nanorobotics, and so forth. Essentially, PSD is also a photodetector based on the lateral photovoltaic effect (LPE). This article reviews recent progress in high-performance PSD based on 2D materials. The high-sensitive photodetectors and LPE involved in 2D photodetectors are firstly discussed. Then, we introduce the research progress of PSD based on 2D materials and analyze the carrier dynamics in different device structures. Finally, we summarize the functionalities and applications of PSD based on 2D materials, and highlight the challenges and opportunities in this research area.

Optical emission efficiency of two-dimensional layered transition metal dichalcogenides (TMDs) is one of the most important parameters affecting their optoelectronic performance. The optimization of the growth parameters by chemical vapor deposition (CVD) to achieve optoelectronic-grade quality TMDs is, therefore, highly desirable. Here, we present a systematic photoluminescence (PL) spectroscopic approach to assess the intrinsic optical and crystalline quality of CVD grown MoS₂ (CVD MoS₂). We propose the use of the intensity ratio between the PL measured in air and vacuum as an effective way to monitor the intrinsic optical quality of CVD MoS₂. Low-temperature PL measurements are also used to evaluate the structural defects in MoS₂, via defect-associated bound exciton emission, which well correlates with the field-effect carrier mobility of MoS₂ grown at different temperatures. This work therefore provides a sensitive, noninvasive method to characterize the optical properties of TMDs, allowing the tuning of the growth parameters for the development of optoelectronic devices.

The electrical performance of two-dimensional transition metal dichalcogenides (TMDs) is strongly affected by the number of structural defects. In this work, we provide an optical spectroscopic characterization approach to correlate the number of structural defects and the electrical performance of WSe₂ devices. Low-temperature photoluminescence (PL) spectra of electron-beam-lithographyprocessed WSe₂ exhibit a clear defect-induced PL emission due to excitons bound to defects, which would strongly degrade the electrical performance. By adopting an electron-beam-free transfer-electrode technique, we successfully prepared a backgated WSe₂ device containing a limited amount of defects. A maximum hole mobility of approximately 200 cm²·V^-1·s^-1 was achieved because of the reduced scattering sources, which is the highest reported value for this type of device. This work provides not only a versatile and nondestructive method to monitor the defects in TMDs but also a new route to approach the room-temperature phonon-limited mobility in high-performance TMD devices.

There have been continuous efforts to seek novel functional two-dimensional semiconductors with high performance for future applications in nanoelectronics and optoelectronics. In this work, we introduce a successful experimental approach to fabricate monolayer phosphorene by mechanical cleavage and a subsequent Ar⁺ plasma thinning process. The thickness of phosphorene is unambiguously determined by optical contrast spectra combined with atomic force microscopy (AFM). Raman spectroscopy is used to characterize the pristine and plasma-treated samples. The Raman frequency of the A_2g mode stiffens, and the intensity ratio of A_2g to A_1g modes shows a monotonic discrete increase with the decrease of phosphorene thickness down to a monolayer. All those phenomena can be used to identify the thickness of this novel two-dimensional semiconductor. This work on monolayer phosphorene fabrication and thickness determination will facilitate future research on phosphorene.