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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 increasing interests in the last decade. The ultrathin feature of 2D materials makes them promising building blocks for next-generation electronic and optoelectronic devices. With reducing dimensionality from 3D to 2D, the inevitable defects will play more important roles in determining the properties of materials. In order to maximize the functionality of 2D materials, deep understanding and precise manipulation of the defects are indispensable. In the recent years, increasing research efforts have been made on the observation, understanding, manipulation, and control of defects in 2D materials. Here, we summarize the recent research progress of defect engineering on 2D materials. The defect engineering triggered by electron beam (e-beam), plasma, chemical treatment, and so forth is comprehensively reviewed. Firstly, e-beam irradiation-induced defect evolution, structural transformation, and novel structure fabrication are introduced. With the assistance of a high-resolution electron microscope, the dynamics of defect engineering can be visualized in situ . Subsequently, defect engineering employed to improve the performance of 2D devices by means of other methods of plasma, chemical, and ozone treatments is reviewed. At last, the challenges and opportunities of defect engineering on promoting the development of 2D materials are discussed. Through this review, we aim to build a correlation between defects and properties of 2D materials to support the design and optimization of high-performance electronic and optoelectronic devices.

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.

Atomically thin Bi 2 O 2 Se has emerged as a novel two-dimensional (2D) material with an ultrabroadband nonlinear optical response, high carrier mobility and excellent air stability, showing great potential for the realization of optical modulators. Here, we demonstrate a femtosecond solid-state laser at 1.0 µm with Bi 2 O 2 Se nanoplates as a saturable absorber (SA). Upon further defect regulation in 2D Bi 2 O 2 Se, the average power of the mode-locked laser is improved from 421 mW to 665 mW, while the pulse width is decreased from 587 fs to 266 fs. Moderate Ar + plasma treatments are employed to precisely regulate the O and Se defect states in Bi 2 O 2 Se nanoplates. Nondegenerate pump-probe measurements show that defect engineering effectively accelerates the trapping rate and defect-assisted Auger recombination rate of photocarriers. The saturation intensity is improved from 3.6 ± 0.2 to 12.8 ± 0.6 MW cm −2 after the optimized defect regulation. The enhanced saturable absorption and ultrafast carrier lifetime endow the high-performance mode-locked laser with both large output power and short pulse duration. Bi 2 O 2 Se holds potential for the realization of 2D optical modulators due to its broadband nonlinear response, air stability and carrier mobility. Here, the authors report the realization of defect-engineered Bi 2 O 2 Se nanoplates as saturable absorbers for femtosecond solid-state lasers, showing improved output power and pulse duration.

The development of next-generation electronics requires scaling of channel material thickness down to the two-dimensional limit while maintaining ultralow contact resistance 1 , 2 . Transition-metal dichalcogenides can sustain transistor scaling to the end of roadmap, but despite a myriad of efforts, the device performance remains contact-limited 3 – 12 . In particular, the contact resistance has not surpassed that of covalently bonded metal–semiconductor junctions owing to the intrinsic van der Waals gap, and the best contact technologies are facing stability issues 3 , 7 . Here we push the electrical contact of monolayer molybdenum disulfide close to the quantum limit by hybridization of energy bands with semi-metallic antimony ( 01 1 ̅ 2 ) through strong van der Waals interactions. The contacts exhibit a low contact resistance of 42 ohm micrometres and excellent stability at 125 degrees Celsius. Owing to improved contacts, short-channel molybdenum disulfide transistors show current saturation under one-volt drain bias with an on-state current of 1.23 milliamperes per micrometre, an on/off ratio over 10 8 and an intrinsic delay of 74 femtoseconds. These performances outperformed equivalent silicon complementary metal–oxide–semiconductor technologies and satisfied the 2028 roadmap target. We further fabricate large-area device arrays and demonstrate low variability in contact resistance , threshold voltage, subthreshold swing, on/off ratio, on-state current and transconductance 13 . The excellent electrical performance, stability and variability make antimony ( 01 1 ̅ 2 ) a promising contact technology for transition-metal-dichalcogenide-based electronics beyond silicon. The electrical contact of two-dimensional transistors is pushed close to the quantum limit by hybridization of the energy bands with antimony; the contacts have low contact resistance and excellent stability.

The realization of room-temperature-operated, high-performance, miniaturized, low-power-consumption and Complementary Metal-Oxide-Semiconductor (CMOS)-compatible mid-infrared photodetectors is highly desirable for next-generation optoelectronic applications, but has thus far remained an outstanding challenge using conventional materials. Two-dimensional (2D) heterostructures provide an alternative path toward this goal, yet despite continued efforts, their performance has not matched that of low-temperature HgCdTe photodetectors. Here, we push the detectivity and response speed of a 2D heterostructure-based mid-infrared photodetector to be comparable to, and even superior to, commercial cooled HgCdTe photodetectors by utilizing a vertical transport channel (graphene/black phosphorus/molybdenum disulfide/graphene). The minimized carrier transit path of tens of nanometers facilitates efficient and fast carrier transport, leading to significantly improved performance, with a mid-infrared detectivity reaching 2.38 × 10 11 cmHz 1/2 W −1 (approaching the theoretical limit), a fast response time of 10.4 ns at 1550 nm, and an ultrabroadband detection range spanning from the ultraviolet to mid-infrared wavelengths. Our study provides design guidelines for next-generation high-performance room-temperature-operated mid-infrared photodetectors. Here, the authors report the realization of room-temperature broadband mid-infrared detectors based on a van der Waals heterostructure with a vertical transport channel, exhibiting specific detectivity and response times comparable or superior to those of commercial cooled HgCdTe photodetectors.

Light encodes multidimensional information, such as intensity, polarization, and spectrum. Traditional extraction of this light information requires discrete optical components by subdividing the detection area into many “one-to-one” functional pixels. The broadband photodetection of high-dimensional optical information with a single integrated on-chip detector is highly sought after, yet it poses significant challenges. In this study, we employ a metasurface-assisted graphene photodetector, enabling to simultaneously detect and differentiate various polarization states and wavelengths of broadband light (1-8 μm) at the wavelength prediction accuracy of 0.5 μm. The bipolar polarizability empowered by this design allows to decouple multidimensional information (encompassing polarization and wavelength), which can be achieved by encoding vectorial photocurrents with varying polarities and amplitudes. Furthermore, cooperative multiport metasurfaces are adopted and boosted by machine learning techniques. It enables precise spin-wavelength differentiation over an extremely broad wavelength range (1-8 μm). Our innovation offers a recipe for highly compact and high-dimensional spectral-polarization co-detection. The detection of light intensity, polarization, and spectral information with a single device is desired for efficient optical sensing and computing applications. Here, the authors report the realization of metasurface-assisted graphene photodetectors able to simultaneously detect polarization states and wavelengths of broadband infrared light.

Multiple structural phases of tellurium (Te) have opened up various opportunities for the development of two-dimensional (2D) electronics and optoelectronics. However, the phase-engineered synthesis of 2D Te at the atomic level remains a substantial challenge. Herein, we design an atomic cluster density and interface-guided multiple control strategy for phase- and thickness-controlled synthesis of α -Te nanosheets and β -Te nanoribbons (from monolayer to tens of μm) on WS 2 substrates. As the thickness decreases, the α -Te nanosheets exhibit a transition from metallic to n-type semiconducting properties. On the other hand, the β -Te nanoribbons remain p-type semiconductors with an ON-state current density (I ON ) up to ~ 1527 μA μm −1 and a mobility as high as ~ 690.7 cm 2 V −1 s −1 at room temperature. Both Te phases exhibit good air stability after several months. Furthermore, short-channel (down to 46 nm) β -Te nanoribbon transistors exhibit remarkable electrical properties (I ON  = ~ 1270 μA μm −1 and ON-state resistance down to 0.63 kΩ μm) at V ds  = 1 V. Phase engineering of 2D tellurium could enable potential applications for (opto-)electronic devices. Here, the authors report the phase- and thickness-controlled synthesis of α-Te nanosheets and β-Te nanoribbons, showing their application for the realization of short-channel transistors.

Spatially tailored pseudo-magnetic fields (PMFs) can give rise to pseudo-Landau levels and the valley Hall effect in graphene. At an experimental level, it is highly challenging to create the specific strain texture that can generate PMFs over large areas. Here, we report that superposing graphene on multilayer black phosphorus creates shear-strained superlattices that generate a PMF over an entire graphene–black phosphorus heterostructure with edge size of tens of micrometres. The PMF is intertwined with the spatial period of the moiré pattern, and its spatial distribution and intensity can be modified by changing the relative orientation of the two materials. We show that the emerging pseudo-Landau levels influence the transport properties of graphene–black phosphorus field-effect transistor devices with Hall bar geometry. The application of an external magnetic field allows us to enhance or reduce the effective field depending on the valley polarization with the prospect of developing a valley filter.

Background/Objectives: Rhamnolipids (RLs) are biosurfactants with significant industrial and environmental potential, which physicochemical properties depend greatly on their fatty acyl chain composition. This study investigated the impact of genetically modulating the fatty acid synthesis genes fabA and fabZ on RL composition and functionality in Pseudomonas aeruginosa PAO1. Methods and Results: Using temperature-sensitive mutants and suppressor strains for these essential genes, we successfully engineered RLs with altered fatty acyl chain lengths and saturation levels. LC–MS/MS analyses showed that deletion and overexpression of fabA and fabZ significantly shifted RL fatty acid profiles. Functional analyses indicated that these structural changes markedly influenced RL emulsification activity and critical micelle concentration (CMC). Conclusions: These findings demonstrate the feasibility of optimizing RL properties through targeted genetic manipulation, offering valuable insights for designing customized biosurfactants for diverse industrial and environmental applications.