Scalable preparation of water-soluble ink of few-layered WSe2 nanosheets for large-area electronics

Few-layer two-dimensional(2D)semiconductor nanosheets with a layer-dependent band gap are attractive building blocks for large-area thin-film electronics.A general approach is developed to fast prepare uniform and phase-pure 2HWSe2 semiconducting nanosheets at a large scale,which involves the supercritical carbon dioxide(SC-CO2)treatment and a mild sonication-assisted exfoliation process in aqueous solution.The as-prepared 2H-WSe2 nanosheets preserve the intrinsic physical properties and intact crystal structures,as confirmed by Raman,x-ray photoelectron spectroscopy(XPS),and scanning transmission electron microscope(STEM).The uniform 2H-WSe2 nanosheets can disperse well in water for over six months.Such good dispersivity and uniformity enable these nanosheets to self-assembly into thickness-controlled thin films for scalable fabrication of large-area arrays of thin-film electronics.The electronic transport and photoelectronic properties of the field-effect transistor based on the self-assembly 2H-WSe2 thin film have also been explored.

Flat multifunctional liquid crystal elements through multi-dimensional information multiplexing

Flat optical elements have attracted enormous attentions and act as promising candidates for the next generation of optical components.As one of the most outstanding representatives,liquid crystal(LC)has been widely applied in flat panel display industries and inspires the wavefront modulation with the development of LC alignment techniques.However,most LC elements perform only one type of optical manipulation and are difficult to realize the multifunctionality and light integration.Here,flat multifunctional liquid crystal elements(FMLCEs),merely composed of anisotropic LC molecules with space-variant orientations,are presented for multichannel information manipulation by means of polarization,space and wavelength multiplexing.Specifically,benefiting from the unique light response with the change of the incident polarization,observation plane,and working wavelength,a series of FMLCEs are demonstrated to achieve distinct near-and far-field display functions.The proposed strategy takes full advantage of basic optical parameters as the decrypted keys to improve the information capacity and security,and we expect it to find potential applications in information encryption,optical anti-counterfeiting,virtual/augmented reality,etc.

Review on metal halide perovskite-based optoelectronic synapses

With the progress of both photonics and electronics,optoelectronic synapses are considered potential candidates to challenge the von Neumann bottleneck and the field of visual bionics in the era of big data.They are also regarded as the basis for integrated artificial neural networks(ANNs)owing to their flexible optoelectronic tunable properties such as high bandwidth,low power consumption,and high-density integration.Over the recent years,following the emergence of metal halide perovskite(MHP)materials possessing fascinating optoelectronic properties,novel MHP-based optoelectronic synaptic devices have been exploited for numerous applications ranging from artificial vision systems(AVSs)to neuromorphic computing.Herein,we briefly review the application prospects and current status of MHP-based optoelectronic synapses,discuss the basic synaptic behaviors capable of being implemented,and assess their feasibility to mimic biological synapses.Then,we focus on the two-terminal optoelectronic synaptic memristors and three-terminal transistor synaptic phototransistors(SPTs),the two essential apparatus structures for optoelectronic synapses,expounding their basic features and operating mechanisms.Finally,we summarize the recent applications of optoelectronic synapses in neuromorphic systems,including neuromorphic computing,high-order learning behaviors,and neuromorphic vision systems,outlining their potential opportunities and future development directions as neuromorphic devices in the field of artificial intelligence(AI).

Cross-Linked Hollow Graphitic Carbon as Low-Cost and High-Performance Anode for Potassium Ion Batteries

Large-scale and low-cost preparation of carbon-based potassium anode with long life and high capacity is one of the footstones for the development of potassium ion batteries(PIBs).Herein,a low-cost carbon-based material,cross-linked hollow graphitic carbon(HGC),is large scale synthesized to apply for PIBs anode.Its hollow structure can afford sufficient space to overcome the damage caused by the volume expansion of graphitic carbon(GC).While the cross-linked structure forms a compact interconnection network that allows electrons to rapid transfer between different GC frameworks.Electrochemical measurements demonstrated that the HGC anode exhibited low charge/discharge plateau(about 0.25 V and 0.1 V)and excellent specific capacity as high as 298 m A h g^(-1)at the current density of 50 m A g^(-1).And more important,after 200 cycles the capacity of HGC anode still shows 269 m A h g^(-1)(the decay rate of per cycle is only 0.048%).Meanwhile,the use of commercial traditional electrolyte(KPF_(6))and cheap raw materials that provide new hope for trying and realizing the large-scale production of PIBs based on carbon anode materials.

Self-powered circularly polarized light detector based on asymmetric chiral metamaterials

Circularly polarized light(CPL)has been given great attention because of its extensive application.While several devices for CPL detection have been studied,their performance is affected by the magnitude of photocurrent.In this paper,a self-powered photodetector based on hot electrons in chiral metamaterials is proposed and optimized.CPL can be distinguished by the direction of photocurrent without external bias owing to the interdigital electrodes with asymmetric chiral metamaterials.Distinguished by the direction of photocurrent,the device can easily detect the rotation direction of the CPL electric field,even if it only has a very weak responsivity.The responsivity of the proposed detector is near 1.9 mA/W at the wavelength of 1322 nm,which is enough to distinguish CPL.The detector we proposed has the potential for application in optical communication.

Realization of semiconducting Cu_(2)Se by direct selenization of Cu(111)

Bulk group IB transition-metal chalcogenides have been widely explored due to their applications in thermoelectrics.However,a layered two-dimensional form of these materials has been rarely reported.Here,we realize semiconducting Cu_(2)Se by direct selenization of Cu(111).Scanning tunneling microcopy measurements combined with first-principles calculations allow us to determine the structural and electronic properties of the obtained structure.X-ray photoelectron spectroscopy data reveal chemical composition of the sample,which is Cu_(2)Se.The observed moire pattern indicates a lattice mismatch between Cu_(2)Se and the underlying Cu(111)-√3×√3 surface.Differential conductivity obtained by scanning tunneling spectroscopy demonstrates that the synthesized Cu_(2)Se exhibits a band gap of 0.78 eV.Furthermore,the calculated density of states and band structure demonstrate that the isolated Cu_(2)Se is a semiconductor with an indirect band gap of-0.8 eV,which agrees quite well with the experimental results.Our study provides a simple pathway varying toward the synthesis of novel layered 2D transition chalcogenides materials.

Signatures of strong interlayer coupling inγ-InSe revealed by local differential conductivity

Interlayer coupling in layered semiconductors can significantly affect their optoelectronic properties.However,understanding the mechanisms behind the interlayer coupling at the atomic level is not straightforward.Here,we study modulations of the electronic structure induced by the interlayer coupling in theγ-phase of indium selenide(γ-InSe)using scanning probe techniques.We observe a strong dependence of the energy gap on the sample thickness and a small effective mass along the stacking direction,which are attributed to strong interlayer coupling.In addition,the moirépatterns observed inγ-InSe display a small band-gap variation and nearly constant local differential conductivity along the patterns.This suggests that modulation of the electronic structure induced by the moirépotential is smeared out,indicating the presence of a significant interlayer coupling.Our theoretical calculations confirm that the interlayer coupling inγ-InSe is not only of the van der Waals origin,but also exhibits some degree of hybridization between the layers.Strong interlayer coupling might play an important role in the performance ofγ-InSe-based devices.

Selective formation of ultrathin PbSe on Ag(111)

Two-dimensional(2D)semiconductors,such as lead selenide(PbSe),locate at the key position of next-generation devices.However,the ultrathin PbSe is still rarely reported experimentally,particularly on metal substrates.Here,we report the ultrathin PbSe synthesized via sequential molecular beam epitaxy on Ag(111).The scanning tunneling microscopy is used to resolve the atomic structure and confirms the selective formation of ultrathin PbSe through the reaction between Ag5Se2 and Pb,as further evidenced by the theoretical calculation.It is also found that the increased accumulation of Pb leads to the improved quality of PbSe with larger and more uniform films.The detailed analysis demonstrates the bilayer structure of synthesized PbSe,which could be deemed to achieve the 2D limit.The differential conductance spectrum reveals a metallic feature of the PbSe film,indicating a certain interaction between PbSe and Ag(111).Moreover,the moirépattern originated from the lattice mismatch between PbSe and Ag(111)is observed,and this moirésystem provides the opportunity for studying physics under periodical modulation and for device applications.Our work illustrates a pathway to selectively synthesize ultrathin PbSe on metal surfaces and suggests a 2D experimental platform to explore PbSe-based opto-electronic and thermoelectric phenomena.

Surface Modification for WSe2 Based Complementary Electronics

High-performance WSe2 complementary transistors are demonstrated on an individual flake by ozone exposure,which relies on the charge transfer mechanism.This technology is readily feasible for modulating the conductivity type in WSe2,and the p–n junction presents a high on-off ratio of 104.Based on robust p-type transistors and matched output current of n-type WSe2 transistors,the complementary inverter achieves a high voltage gain of 19.9.Therefore,this strategy may provide an avenue for development of high-performance complementary electronics.

Chlorine doped graphitic carbon nitride nanorings as an efficient photoresponsive catalyst for water oxidation and organic decomposition

Rationally engineering the microstructure and electronic structure of catalysts to induce high activity for versatile applications remains a challenge. Herein, chlorine doped graphitic carbon nitride(Cl-doped g-C3N4) nanorings have been designed as a superior photocatalyst for pollutant degradation and oxygen evolution reaction(OER). Remarkably, Cl-doped g-C3N4 nanorings display enhanced OER performance with a small overpotential of approximately 290 m V at current density of 10 m A cm^-2 and Tafel slope of 83 m V dec-1, possessing comparable OER activity to precious metal oxides RuO2 and IrO2/C. The excellent catalytic performance of Cl-doped g-C3N4 nanorings originates from the strong oxidation capability,abundant active sites exposed and efficient charge transfer. More importantly, visible light irradiation gives rise to a prominent improvement of the OER performance, reducing the OER overpotential and Tafel slope by 140 m V and 28 m V dec^-1, respectively, demonstrating the striking photo-responsive OER activity of Cl-doped g-C3N4 nanorings. The great photo-induced improvement in OER activity would be related to the efficient charge transfer and the·OH radicals arising spontaneously on CN-Cl100 catalyst upon light irradiation. This work establishes Cl-doped g-C3N4 nanorings as a highly competitive metal-free candidate for photoelectrochemical energy conversion and environmental cleaning application.

Fe_(0.8)CoSe_(2) nanosphere coated by N-doped carbon for ultra- high rate potassium selenium battery

Potassium-selenium(K-Se) batteries are a promising electrical energy storage candidate because of the cost-effectiveness and material sustainability, yet they suffer from shuttle effect, volume expansion and low powder density. The development of Se-based cathode is an effective way to overcome the above issues. Here we designed a hollow nano-spherical Co-Fe bi-metallic selenide coated with N-doped carbon(denoted as CFS@N-C)as cathode for K-Se batteries. Bimetallic selenide is benefit to improve the conductivity of composite materials;N-doped carbon layer encapsulation effectively inhibits the dissolution of poly-selenides and relieves the volume expansion. The as-prepared K-Se battery exhibits excellent rate performance(300 mAh·g^(-1) at 1000 mA·g^(-1)) and slowcharge/ultrafast-dischargecapability(dischargeat5000 mA·g^(-1) and charge at 100 mA·g^(-1) with ultrahigh capacity of 227 mAh·g^(-1)) with Coulombic efficiency nearly 100%. In addition, the ex-situ high-resolution transmission electron microscopy(HRTEM) images reveal that the charge–discharge mechanism of CFS@N-C is K^(+) replaces the bimetal and forms K_(2)Se. The unique design in this work may provide certain directions on researching for high power density K-storage materials.

Quasiperiodic photonic crystal fiber[Invited]

In the fields of light manipulation and localization,quasiperiodic photonic crystals,or photonic quasicrystals[PQs],are causing an upsurge in research because of their rotational symmetry and long-range orientation of transverse lattice arrays,as they lack translational symmetry.It allows for the optimization of well-established light propagation properties and has introduced new guiding features.Therefore,as a class,quasiperiodic photonic crystal fibers,or photonic quasicrystal fibers[PQFs],are considered to add flexibility and richness to the optical properties of fibers and are expected to offer significant potential applications to optical fiber fields.In this review,the fundamental concept,working mechanisms,and invention history of PQFs are explained.Recent progress in optical property improvement and its novel applications in fields such as dispersion control,polarization-maintenance,supercontinuum generation,orbital angular momentum transmission,plasmon-based sensors and filters,and high nonlinearity and topological mode transmission,are then reviewed in detail.Bandgap-type air-guiding PQFs supporting low attenuation propagation and regulation of photonic density states of quasiperiodic cladding and in which light guidance is achieved by coherent Bragg scattering are also summarized.Finally,current challenges encountered in the guiding mechanisms and practical preparation techniques,as well as the prospects and research trends of PQFs,are also presented.

Photonic and phononic interface states based on sunflower-type crystals[Invited]

Interface states are widely applied in waveguide devices.However,previous studies failed to achieve photonic and phononic interface states independent of each other in the same crystal structure depending on the behavior of the crystal structure,i.e.,photonic or phononic crystals,making the function of interface states single.In this study,straight-line and circular photonic and phononic interface states were realized independently in sunflower-type crystals.In addition,with a defect and a metal barrier,interface states could remain almost undamaged.The results have the potential to achieve multifunction devices and reduce the cost of engineering applications.

非晶态硼掺杂石墨相氮化碳量子点:近90%高荧光量子产率及高灵敏检测Fe^(2+)/Cd^(2+)

石墨相氮化碳量子点(CNQDs)作为一种具有吸引力的光致发光(PL)材料,在荧光成像和重金属离子检测方面具有巨大的潜力.然而,晶态CNQDs的商业化应用仍被其低荧光量子产率、自猝灭和激发波长依赖行为所限制.我们提出利用硼掺杂和CNQDs非晶化的协同策略——通过水热和自上而下的超声剥离方法制备非晶态硼掺杂CNQDs(B-CNQDs)——以解决以上三个问题.结构无序赋予了非晶态B-CNQDs大范围pH下优越的弹性应变性能,从而可以有效促进电荷传输,减少激子猝灭.同时,通过形成均匀的硼掺杂表面态,可以巧妙地调节CNQDs的电子结构和荧光发射特性,实现无激发波长依赖行为.结果表明,非晶态B-CNQDs具有优异的荧光稳定性(2年后无明显衰减),且具有87.4%的高量子产率,是非常有前途的荧光材料.在紫外光激发下,B-CNQDs在商业用纸上可以显示出特定图形的亮蓝色荧光.此外,B-CNQDs对Fe^(2+)和Cd^(2+)在ppb检测范围内具有高度的选择性和灵敏度.本工作可为开发具有高稳定性和高量子产率的非晶态碳基荧光材料用于光电器件和传感器提供实验基础和有益启示.

SbVO4 based high capacity potassium anode:a combination of conversion and alloying reactions

As the key to optimizing potassium ion batteries’(PIBs)performance,the development of high capacity potassium anode is the footstone.Here,through a one-step solvothermal method,uniformly dispersed SbVO4 nanoparticles on the reduced graphene oxide nanosheets(SbVO4@RGO)were synthesized and used as PIBs anodes.SbVO4@RGO anode shows high capacity due to alloying and conversion reactions occur simultaneously in the cyclic process.The anode delivers a capacity as high as 447.9 mAh g^-1 at 100 mA g^-1.Besides,a cycling life of 500 cycles with small average capacity decay rate(only 0.106%per cycle)is also revealed.It was found in the initial discharge process,SbVO4 transforms into Sb and K3VO4.And in the following cycle Sb and K3VO4 simultaneously react with K+via the alloying/de-alloying and conversion reaction,respectively.The present study of SbVO4@RGO may provide insight for high performance alloying-based/conversion-based potassium anodes.

Hollow-core photonic quasicrystal fiber with high birefringence and ultra-low nonlinearity

A hollow-core fiber based on photonic quasicrystal arrays is theoretically proposed for high-quality light wave propagation with high polarization maintaining performance and low nonlinearity.This fiber,called hollow-core photonic quasicrystal fiber(HC-PQF),can simultaneously realize a high birefringence that reaches 1.345×10^-2 and a small nonlinear coefficient of 1.63×10^-3 W^-1·km^-1 at a communication wavelength of 1.55μm due to the air-filled core and unique quasiperiodic fiber structure.To further demonstrate the controllability of the nonlinear coefficient and the application of sensor and polarization-maintaining fiber,the nonlinearity is investigated by filling different inert gases in the fiber core while the birefringence keeps a high order of 10-2.In the wavelength rangeλ∈[1.53μm,1.57μm],the dispersion is near zero and flattened.The HC-PQF is expected to be used for applications in optical communication,high power pulse transmission,polarization beam splitters,etc.

Optical edge detection with adjustable resolution based on liquid crystal polarization gratings

Optical edge detection, a part of image processing, plays an important role in extracting image information used in optical analog computation. In this Letter, we raise a new way to realize optical edge detection. This design is based on two liquid crystal polarization gratings with a period of 2.2 mm, which function as a spatial differentiator. We experimentally demonstrate broadband optical detection and real-time adjustable resolution.The proposed method takes advantage of the convenience to use, simple fabrication process, and real-time tunable resolution. It may guide more significant applications in the optical field and other practical scenarios like machine vision in computers.

Multiple super-resolution imaging in the second band of gradient lattice spacing photonic crystal flat lens

Based on the triangular lattice two-dimensional photonic crystal(PC), the lattice spacing along the transverse direction to propagation is altered, and a gradient PC(GPC) flat lens is designed. The band structures and equal frequency curves of the GPC are calculated;then, the imaging mechanism and feasibility are analyzed. The imaging characteristics of the GPC flat lens are investigated. It is observed that the GPC can achieve multiple types of super-resolution imaging for the point source. This GPC lens is allowed to be applied to imaging and other fields such as filtering and sensing.

Ferroelectric-gated ReS_(2)field-effect transistors for nonvolatile memory

Ferroelectric field-effect transistors(FeFET)with nondestructive readout capability have emerged as an attractive candidate for next-generation nonvolatile memory technology.Herein,we demonstrate ferroelectric-gated nonvolatile memory featuring a top gate architecture by combining multi-layer ReS_(2)with ferroelectric poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE))copolymer films.The ReS_(2)FeFET using hBN as substrate shows a large memory window of~30 V.Repeated write/erase operations are successfully performed by applying pulse voltage of±25 V with 1 ms width to the ferroelectric P(VDF-TrFE),and an ultra-high write/erase ratio of~107 can be achieved.Furthermore,the ReS_(2)FeFET shows stable data retention capability of longer than 2,000 s and reliable endurance of greater than 2,000 cycles.These characteristics highlight that such ferroelectricgated nonvolatile memory has great potential in future non-volatile memory applications.

碳纤维中可控修饰FeV_(2)S_(4)及其高容量长寿命储钠研究

拥有高比容量的金属硫化物作为负极材料在钠离子电池(SIBs)领域备受关注.FeV_(2)S_(4)作为一种典型的金属硫化物,由于体积变化大,存在容量衰减快、稳定性差的问题.本文利用氧化石墨烯(GO)实现了对FeV_(2)S_(4)纳米粒子尺寸和分布的调控,使其更好地包裹在碳纳米纤维(CNFs)中,从而制备了FeV_(2)S_(4)@GO@CNF.FeV_(2)S_(4)@GO@CNF负极与表面拥有更多粒子的FeV_(2)S_(4)@CNF负极相比具有更优异的Na+存储性能.FeV_(2)S_(4)@GO@CNF用于钠离子电池负极时,200次循环(0.1 A g^(−1))后容量仍然可保持在411 mA h g^(−1),500次循环(1 A g^(−1))后可保持在227 mA h g^(−1).此外,在0℃下,经过150次循环(0.1 A g^(−1))后,仍可以输出170.2 mA h g−1的容量.以FeV_(2)S_(4)@GO@CNF作为负极,Na_(3)V_(2)(PO4)3/C作为正极的全电池在0.5 A g^(−1)下循环100次后,其容量达到164 mA h g^(−1).FeV_(2)S_(4)@GO@CNF表现出高比容量和稳定性,这是由于GO控制了FeV_(2)S_(4)的颗粒大小及其在CNFs中的分布,从而提高了FeV_(2)S_(4)@GO@CNF的稳定性.本研究为纳米CNF复合材料的制备提供了新思路.