Revealing the Intrinsic Peroxidase-Like Catalytic Mechanism of Heterogeneous Single-Atom Co-MoS2

The single-atom nanozyme is a new concept and has tremendous prospects to become a next-generation nanozyme.However,few studies have been carried out to elucidate the intrinsic mechanisms for both the single atoms and the supports in single-atom nanozymes.Herein,the heterogeneous single-atom Co-MoS2(SA Co-MoS2)is demonstrated to have excellent potential as a high-performance peroxidase mimic.Because of the well-defined structure of SA Co-MoS2,its peroxidase-like mechanism is extensively interpreted through experimental and theoretical studies.Due to the different adsorption energies of substrates on different parts of SA Co-MoS2 in the peroxidase-like reaction,SA Co favors electron transfer mechanisms,while MoS2 relies on Fenton-like reactions.The different catalytic pathways provide an intrinsic understanding of the remarkable performance of SA Co-MoS2.The present study not only develops a new kind of single-atom catalyst(SAC)as an elegant platform for understanding the enzyme-like activities of heterogeneous nanomaterials but also facilitates the novel application of SACs in biocatalysis.

Band structure engineering in metal halide perovskite nanostructures for optoelectronic applications

Metal halide perovskite nanostructures have emerged as low-dimensional semiconductors of great significance in many fields such as photovoltaics,photonics,and optoelectronics.Extensive efforts on the controlled synthesis of perovskite nanostructures have been made towards potential device applications.The engineering of their band structures holds great promise in the rational tuning of the electronic and optical properties of perovskite nanostructures,which is one of the keys to achieving efficient and multifunctional optoelectronic devices.In this article,we summarize recent advances in band structure engineering of perovskite nanostructures.A survey of bandgap engineering of nanostructured perovskites is firstly presented from the aspects of dimensionality tailoring,compositional substitution,phase segregation and transition,as well as strain and pressure stimuli.The strategies of electronic doping are then reviewed,including defect-induced self-doping,inorganic or organic molecules-based chemical doping,and modification by metal ions or nanostructures.Based on the bandgap engineering and electronic doping,discussions on engineering energy band alignments in perovskite nanostructures are provided for building high-performance perovskite p-n junctions and heterostructures.At last,we provide our perspectives in engineering band structures of perovskite nanostructures towards future low-energy optoelectronics technologies.

Graphene plasmonic nanoresonators/graphene heterostructures for efficient room-temperature infrared photodetection

High-performance infrared(IR)photodetectors made by low dimensional materials promise a wide range of applications in communication,security and biomedicine.Moreover,light-harvesting effects based on novel plasmonic materials and their combinations with two-dimensional(2 D)materials have raised tremendous interest in recent years,as they may potentially help the device complement or surpass currently commercialized IR photodetectors.Graphene is a particularly attractive plasmonic material because graphene plasmons are electrically tunable with a high degree of electromagnetic confinement in the mid-infrared(mid-IR)to terahertz regime and the field concentration can be further enhanced by forming nanostructures.Here,we report an efficient mid-IR room-temperature photodetector enhanced by plasmonic effect in graphene nanoresonators(GNRs)/graphene heterostructure.The plasmon polaritons in GNRs are size-dependent with strong field localization.Considering that the size and density of GNRs are controllable by chemical vapor deposition method,our work opens a cost-effective and scalable pathway to fabricate efficient IR optoelectronic devices with wavelength tunability.

Strong interactions in molybdenum disulfide heterostructures boosting the catalytic performance of water splitting: A short review

Two-dimensional materials(2DMs) have attracted substantial attention due to their abundant active sites and their ultrahigh surface area for different catalytic applications due to the high lateral-longitudinal ratio. Transition metal dichalcogenides(TMDs), especially MoS2, as one of the 2DMs most often studied, have shown superior activity in electrochemical applications. Recently, combinations of different 2DMs have been widely studied, and they appear to be the most promising strategy available to develop state of the art catalysts for different reactions.In this article, we review the interactions between MoS2 and other materials as well as the novel assembly induced phase transitions of TMDs and their underlying mechanisms. Several methods for inducing the phase transition of TMDs by building MoS2-based heterostructures have been introduced. The electronic coupling between these counterparts has significantly enhanced their conductivity and optimized the energy states of the materials, thus introducing enhanced activity as compared to their original counterparts. The ideas summarized in this article may shed new light on and help to develop next-generation green energy materials by designing and constructing highly active two-dimensional catalysts for efficient water splitting.

Editorial for a special issue on two-dimensional nanomaterials

The isolation of single layer graphene and its outstanding physical,chemical and mechanical properties has paved the way for both exploring the existing layered materials and developing novel twodimensional(2D)nanomaterials.The science behind 2D nanomaterials is beautiful and closely related to the dimensionality effect.In the past few years,tremendous efforts have been made investigating the material’s preparation,characterizing its fundamental properties and demonstrating its technological applications.In particular,the emergence of 2D organic semiconductors and 2D non-layered organic-inorganic hybrid perovskites have led to new opportunities for cost-effective electronics and green energy applications.

Robust asymmetric Cherenkov radiation in tilted anisotropic medium

Cherenkov radiation(CR)is available for a wide variety of terahertz(THz)radiation sources,but its efficiency is deeply affected by intrinsic losses.We find that if the tilted angle(α)of anisotropic material and radiation angle(θ)meet the condition ofθ+α=π/2,the intensity of radiation fields for the charged particle bunch(CPB)moving from left to right cannot be influenced by intrinsic losses,which means long-distance radiation can be achieved.Furthermore,we observe an asymmetric CR when the CPB moves from the opposite direction.In addition,we select natural van der Waals(vd W)materialα-MoO3as an example,further confirming that the radiation field can reach the far field and the asymmetric CR radiation can also be observed.These wonderful properties with long-distance radiation will extend the application of CR to a certain extent for future design and fabrication.

Monolayer Graphene as a Saturable Absorber in a Mode-Locked Laser

我们证明单层 graphene 的内在的性质允许它当时，为锁模式的纤维激光充当一个更有效的可饱和的吸收器与多层的 graphene 相比。单层 graphene 的吸收能与多层的 graphene，有像皱纹的缺点的 graphene，或 functionalized graphene 相比在更低的刺激紧张被浸透。单层 graphene 有 65.9% 的显著地大的调整深度，而多层的 graphene 的调整深度极大地由于 nonsaturable 吸收被减少并且散布损失。微微秒 ultrafast 激光脉搏(1.23 ps ) 能作为一个可饱和的吸收器用单层 graphene 被产生。由于 ultrafast 松驰时间，更大的调整深度和单层 graphene 的更低的散布损失，它以塑造能力，脉搏稳定性，和产量精力的脉搏比多层的 graphene 更好表现。

Diffraction-limited imaging with monolayer 2D material-based ultrathin flat lenses

Ultrathin flat optics allow control of light at the subwavelength scale that is unmatched by traditional refractive optics.To approach the atomically thin limit,the use of 2D materials is an attractive possibility due to their high refractive indices.However,achievement of diffraction-limited focusing and imaging is challenged by their thickness-limited spatial resolution and focusing efficiency.Here we report a universal method to transform 2D monolayers into ultrathin flat lenses.Femtosecond laser direct writing was applied to generate local scattering media inside a monolayer,which overcomes the longstanding challenge of obtaining sufficient phase or amplitude modulation in atomically thin 2D materials.We achieved highly efficient 3D focusing with subwavelength resolution and diffractionlimited imaging.The high focusing performance even allows diffraction-limited imaging at different focal positions with varying magnifications.Our work paves the way for downscaling of optical devices using 2D materials and reports an unprecedented approach for fabricating ultrathin imaging devices.

Wide-field in situ multiplexed Raman imaging with superresolution

Because of the fingerprint-like specificity of its characteristic spectrogram, Raman spectral imaging has been applied widely in various research areas. Using a combination of structured illumination with the surface-enhanced Raman scattering(SERS) technique, wide-field Raman imaging is developed with a significant improvement in spatial resolution. As a result of the relatively narrow Raman characteristic peaks, optically encoded SERS nanoparticles can be used to perform multiplexed imaging. The results show excellent superresolution wide-field multiplexed imaging performance. The developed technique has extraordinary potential for applications in biological imaging and other related fields.

Anisotropic polaritons in van der Waals materials

Polaritons in two-dimensional(2D)materials continues to garner significant attention due to their favorable ability of field-confinement and intriguing potential for low-loss and ultrafast optical and photonic devices.The recent experimental observation of in-plane anisotropic dispersion in natural van der Waals materials has revealed much richer physics as compared to isotropic plasmonic materials,which provides new insight to manipulate the polaritons and manufacture flat optical devices with unprecedented controls.Herein,we give an overview of the recent progress in in-plane anisotropic polaritons launched and visualized in the near-field range in 2D layered van der Waals materials.Furthermore,future prospects in this promising but emerging field are featured on the basis of its peculiar applications.This review article will stimulate the scientific community to explore other hyperbolic materials and structures in order to develop optical technologies with novel functionalities and further improve the understanding of the exotic photonic phenomena.

中间相促进CsPbIBr_(2)晶体生长以消除高效无机钙钛矿太阳能电池的卤素相分离

混合卤化物钙钛矿材料由于易于调整光学带隙,在叠层太阳能电池、光伏建筑一体化和波长可调的发光器件等方面显示出诱人的应用前景.然而,混合卤化物钙钛矿材料在光照或电荷注入的条件下,卤素离子会产生相分离,从而影响光学带隙的稳定性和器件性能的稳定性,严重阻碍其应用前景.本文中,我们将过量PbBr_(2)或CsI加入到最初等化学计量比的PbBr_(2)和CsI前驱体溶液中.当PbBr_(2)过量时,我们观察到CsPbIBr_(2)钙钛矿晶粒尺寸增大,晶界和CsPbIBr_(2)/TiO2的异质结界面处的卤化物相分离得到抑制;少数载流子寿命增加,电流密度-电压(J-V)滞后减弱,太阳能电池性能提高.然而当CsI过量时,所观察到的结果与前者恰恰相反.这是因为在前驱体溶液中加入过量PbBr_(2),有利于形成Pb(I,Br)2·DMSO络合物和准二维CsPb_(2)(I,Br)5中间相,大大促进了CsPbIBr_(2)晶体的生长和缺陷的消除.因此,通过控制CsPbIBr_(2)前体溶液中的化学成分,引入中间相,促进晶体的生长,从而有效缓解混合卤化物无机CsPbIBr_(2)太阳能电池中的卤化物相分离和器件的J-V迟滞.制备的CsPbIBr_(2)太阳能电池的最高光电转化效率达到9.37%(稳态效率达到8.48%),最大外量子效率超过90%.

Highly stable and repeatable femtosecond soliton pulse generation from saturable absorbers based on twodimensional Cu3-xP nanocrystals

Heavily doped colloidal plasmonic nanocrystals have attracted great attention because of their lower and adjustable free carrier densities and tunable localized surface plasmonic resonance bands in the spectral range from near-infra to mid-infra wavelengths.With its plasmon-enhanced optical nonlinearity,this new family of plasmonic materials shows a huge potential for nonlinear optical applications,such as ultrafast switching,nonlinear sensing,and pulse laser generation.Cu3-xP nanocrystals were previously shown to have a strong saturable absorption at the plasmonic resonance,which enabled high-energy Q-switched fiber lasers with 6.1μs pulse duration.This work demonstrates that both high-quality mode-locked and Q-switched pulses at 1560 nm can be generated by evanescently incorporating two-dimensional(2D)Cu3-xP nanocrystals onto a D-shaped optical fiber as an effective saturable absorber.The 3 dB bandwidth of the mode-locking optical spectrum is as broad as 7.3 nm,and the corresponding pulse duration can reach 423 fs.The repetition rate of the Q-switching pulses is higher than 80 kHz.Moreover,the largest pulse energy is more than 120μJ.Note that laser characteristics are highly stable and repeatable based on the results of over 20 devices.This work may trigger further investigations on heavily doped plasmonic 2D nanocrystals as a next-generation,inexpensive,and solution-processed element for fascinating photonics and optoelectronics applications.

Introduction to two-dimensional layered materials for ultrafast lasers

We introduce the background and motivation of this feature issue of two-dimensional layered materials for ultrafast lasers. A brief summary of the seven collected articles in this feature issue is also given.

Probing the dynamic structural changes of DNA using ultrafast laser pulse in graphene-based optofluidic device

The ultrafast monitoring of deoxyribonucleic acid(DNA)dynamic structural changes is an emerging and rapidly growing research topic in biotechnology.The existing optical spectroscopy used to identify different dynamical DNA structures lacks quick response while requiring large consumption of samples and bulky instrumental facilities.It is highly demanded to develop an ultrafast technique that monitors DNA structural changes with the external stimulus or cancer-related disease scenarios.Here,we demonstrate a novel photonic integrated graphene-optofluidic device to monitor DNA structural changes with the ultrafast response time.Our approach is featured with an effective and straightforward design of decoding the electronic structure change of graphene induced by its interactions with DNAs in different conformations using ultrafast nanosecond pulse laser and achieving refractive index sensitivity of~3×10^(−5) RIU.This innovative technique for the first time allows us to perform ultrafast monitoring of the conformational changes of special DNA molecules structures,including G-quadruplex formation by K+ions and i-motif formation by the low pH stimulus.The graphene-optofluidic device as presented here provides a new class of label-free,ultrafast,ultrasensitive,compact,and cost-effective optical biosensors for medical and healthcare applications.

Growth of large-area atomically thin MoS2 film via ambient pressure chemical vapor deposition

Atomically thin MoS2 films have attracted significant attention due to excellent electrical and optical properties.The development of device applications demands the production of large-area thin film which is still an obstacle.In this work we developed a facile method to directly grow large-area MoS2 thin film on Si O2 substrate via ambient pressure chemical vapor deposition method. The characterizations by spectroscopy and electron microscopy reveal that the as-grown MoS2 film is mainly bilayer and trilayer with high quality. Back-gate field-effect transistor based on such MoS2 thin film shows carrier mobility up to 3.4 cm2V-1s-1 and on/off ratio of 105. The large-area atomically thin MoS2 prepared in this work has the potential for wide optoelectronic and photonic device applications.

Black phosphorus induced photo-doping for high-performance organic-silicon heterojunction photovoltaics

In conventional crystalline silicon （Si） homojunction solar cells,a strategy of doping by transporting phosphorus or boron impurities into Si is commonly used to build Ohmic contacts at rear electrodes.However,this technique involves an energy intensive,high temperature （～ 800 ℃） process and toxic doping materials.Black phosphorus （BP） is a two-dimensional,narrow bandgap semiconductor with high carrier mobility that exhibits broad light harvesting properties.Here,we place BP：zinc oxide （ZnO） composite films between Si and aluminum （Al） to improve their contact.Once the BP harvests photons with energies below 1.1 eV from the crystalline Si,the ZnO carrier concentration increases dramatically due to charge injection.This photo-induced doping results in a high carrier concentration in the ZnO film,mimicking the modulated doping technique used in semiconductor heterojunctions.We show that photo-induced carriers dramatically increase the conductivities of the BP-modified ZnO films,thus reducing the contact resistance between Si and Al.A photovoltaic power conversion efficiency of 15.2% is achieved in organic-Si heterojunction solar cells that use a ZnO：BP layer.These findings demonstrate an effective way of improving Si/metal contact via a simple,low temperature process.

Effects of edge on graphene plasmons as revealed by infrared nanoimaging

We used scattering-type scanning near-field optical microscopy(s-SNOM)to investigate the plasmonic properties of edges in well-defined graphene nanostructures,including sharp tapers,nanoribbons and nanogaps,which were all fabricated via the growth-etching chemical vapor deposition(GECVD)method.The obtained near-field images revealed the localized plasmon modes along the graphene nanoribbon;these modes strongly depended on the size of the graphene pattern,the angle of the tapered graphene and the infrared excitation wavelength.These interesting plasmon modes were verified by numerical simulations and explained by the reflection,and interference of electromagnetic waves at the graphene–SiO_(2) edge.The constructive interference at the graphene nanogap caused by charge accumulation was demonstrated for the first time.Using the infrared nanoimaging technique,greater plasmon broadening was observed in the zigzag edge than in the armchair edge.Our study suggests that graphene edges should be separated by an effective working distance to avoid the overlapping of localized plasmon modes,which is very important for the design of graphene-based plasmonic circuits and devices.

Unraveling the synergetic mechanism of physisorption and chemisorption in laser-irradiated monolayer WS_(2)

To further improve the quantum efficiency of atomically thin transition metal dichalcogenides (TMDs) is crucial for the realization of high-performance optoelectronic applications. To this regard, a few chemical or physical approaches such as superacid treatment, electrical gating, dielectric screening, and laser irradiation have been developed. In particular, the laser irradiation appears to be a more efficient way with good processability and spatial selectivity. However, the underlying mechanism especially about whether chemisorption or physisorption plays a more important role is still debatable. Here, we unravel the mystery of laser irradiation induced photoluminescence enhancement in monolayer WS_(2) by precisely controlling irradiation time and environment. It is found that the synergetic effect of physisorption and chemisorption is responsible for the photoluminescence enhancement, where the physisorption dominates with more than 74% contribution. The comprehensive understanding of the adsorption mechanism in laser-irradiated TMDs may trigger the potential applications for patterned light source, effective photosensor and ultrathin optical memory.

Editorial for special issue on extraordinary 2D-materials-based nanophotonics

The emergence of new materials can push scientific development and even lead to a new industrial revolution. The discovery of graphene has attracted more and more attention from society due to their excellent optics and electricity properties. Graphene has been widely used in optoelectronic devices, such as an optical modulator, polarizer, photoelectric detector, and ultrafast laser. In addition, there is a remarkable transition towards other nanomaterials in recent years.Apart from topological insulators (TIs).

Editorial for special issue on photonics based on two-dimensional noncarbon materials

Scientists are in the constant search of novel materials,or innovative applications of existing materials to solve problems we face in our everyday life.Although graphene,the two-dimensional（2D）form of carbon,has been a star player for the past decade,there is a significant shift towards other noncarbon materials in recent years.Apart from the large family of transition metal dichalcogenides（TMDs）,mono-elemental materials,such as phosphorene,arsenene,antimonene.