High sensitivity SPR sensor for liquid phase sample with Ag/PbS/Graphene hybrid nanostructure

A surface plasmon resonance(SPR)sensor with Ag/PbS/GR hybrid nanostructure has been proposed for the diagnostics of liquid phase samples.Here Ag/PbS/GR hybrid nanostructure is designed as an asymmetric MIM waveguide for surface plasmon.Due to the guided wave SPR(GWSPR)modes,the index of the liquid phase samples can be measured more accurately than the conventional SPR sensors.Numerical simulation results show that the sensitivity of the sensor is about 5 times higher than the conventional SPR sensors.The origin of the enhancement mechanism is the combination of GWSPR in the Ag/PbS/GR hybrid nanostructure which enables the surface plasmon to spread along the PbS layer.In Ag/PbS/GR hybrid nanostructure,the electric field is concentrated mostly in the PbS layer,and the enhancement of the field intensity is nearly30%.

AlGaN solar‐blind APD with low breakdown voltage

A p-i-i-n type AlG a N heterostructure avalanche photodiodes(APDs)is proposed to decrease the avalanche breakdown voltage and to realize higher gain by using high-Al-content AlG aN layer as multiplication layer and low-Al-content AlG aN layer as absorption layer.The calculated results show that the designed APD can significantly reduce the breakdown voltage by almost 30%,and about sevenfold increase of maximum gain compared to the conventional Al GaN APD.The noise in designed APD is also less than that in conventional APD due to its low dark current at the breakdown voltage point.Moreover,the one-dimensional(1D)dual-periodic photonic crystal(PC)with anti-reflection coating filter is designed to achieve the solar-blind characteristic and cutoff wavelength of 282 nm is obtained.

Research on Irradiation Electric Field for Charged Particles Beam with High Energy

Irradiation protection of the nonlinear optical devices used in the spacecraft and next generation active laser system must be solved. The first problem was to find the irradiation damage mechanism of the nonlinear materials. In this paper the irradiation electronic field originating from high speed charged particle beams was discussed. The calculating model of the electronic field, based on the relativistic mechanics and electro-magnetic theory, was founded. The common characters of the irradiation electronic field were predicted and the fields of α ray and β ray were calculated by means of our model. The simulating results showed that the intensity of the electric field increased with the energy or the intensity of the beam. The results also showed that the field change trend of α ray and β ray was similar, but the field value was quite different. When the beam intensity I = 100 μA and the beam energy εm = 500 Mev, the electronic field values were about 3.5 × 107 v/m for α ray and 2.4 × 1011 v/m for β ray.

Microscopic insights into the catalytic mechanisms of monolayer MoS2 and its heterostructures in hydrogen evolution reaction

Exploring high-efficient catalysts for hydrogen evolution reaction(HER)has become very urgeht for resolving the energy related issues.Recently,two-dimensional layered MoS2 and its heterostructures with graphene or other traditional photocatalysts have presented great potentials for electrocatalytic and photocatalytic HER applications.On-site investigations of the atomic-scale structures and local electronic properties of the catalytically active sites are the key points for understanding the internal mechanisms,which however are hard to be achievec from the practical systems.Hereby,this review focuses on the recent progresses on the on-site scanning tunneling microscopy/spectroscopy investigations of the atomic structures and electronic properties of the ultrahigh-vacuum deposited and chemical vapor deposition(CVD)synthesized monolayer MoS2 and MoSz/graphene vertical stacks on the electrodes of Au(111)and Au foils.The correlations between the respective HER activities,edge types and edge electronic states are comparatively introduced.Secondly,this review also introduces thephotocatalytic HER applications of CVD-grown MoS2/WS2 and WS/MoS2 vertical stacks on Au foils,mainly considering of their type-ll band.alignments and the novel interlayer charge transfer behaviors.Finally,future research directions are also proposed for in-depth understanding of the catalytic mechanism,as well as for exploring more efficient HER catalysts.

Chemical vapor deposition of monolayer WS2 nano- sheets on Au foils toward direct application in hydrogen evolution

Monolayer tungsten disulfide （WS2）, a typical member of the semiconducting transition metal dichalcogenide family has drawn considerable interest because of its unique properties. Intriguingly the edge of WS2 exhibits an ideal hydrogen binding energy which makes WS2 a potential alternative to Pt-based electrocatalysts for the hydrogen evolution reaction （HER）. Here, we demonstrate for the first time the successful synthesis of uniform monolayer WS2 nanosheets on centimeter- scale Au foils using a facile, low-pressure chemical vapor deposition method. The edge lengths of the universally observed triangular WS2 nanosheets are tunable from -100 to N1,000 nm. The WS2 nanosheets on Au foils featuring abundant edges were then discovered to be efficient catalysts for the HER, exhibiting a rather high exchange current density of -30.20 μA/cm2 and a small onset potential of Nl10 mV. The effects of coverage and domain size （which correlate closely with the active edge density of WS2） on the electrocatalytic activity were investigated. This work not only provides a novel route toward the batch-production of monolayer WS2 via the introduction of metal foil substrates but also opens up its direct application for facile HER.

Application of chemical vapor-deposited monolayer ReSe2 in the electrocatalytic hydrogen evolution reaction

Controlled synthesis of structurally anisotropic rhenium diselenide （ReSe2） with macroscopically uniform and strictly monolayer thickness as well as tunable domain shape/size is of great interest for electronics-, optoelectronics-, and electrocatalysis-related applications. Herein, we describe the controlled synthesis of uniform monolayer ReSe2 flakes with variable morphology （sunflower- or truncated-triangle-shaped） on SiO2/Si substrates using different ambient-pressure chemical vapor deposition （CVD） setups. The prepared polycrystalline ReSe2 flakes were transferred intact onto Au foil electrodes and tested for activity in the hydrogen evolution reaction （HER）. Interestingly, compared to the compact truncated-triangle-shaped ReSe2 flakes, their edge-abundant sunflower-shaped counterparts exhibited superior electrocatalytic HER activity, featuring a relatively low Tafel slope of - 76 mV/dec and an exchange current density of 10.5 μA/cm2. Thus, our work demonstrates that CVD-grown ReSe2 is a promising two- dimensional anisotropic material for applications in the electrocatalytic HER.

Space-confined growth of monolayer ReSe2 under a graphene layer on Au foils

Vertical heterostructures based on two-dimensional(2D)materials have attracted widespread interest for their numerous applications in electronic and optoelectronic devices.Herein,we report the direct construct!on of an abnormal graphene/ReSe2 stack on Au foils by a two-step chemical vapor deposition(CVD)strategy.During the second growth stage,mono layer ReSe2 is found to prefere ntially evolve at the irUerface between the first-grown graphene layer and the Au substrate.The unusual stacking behavior is unraveled by in-situ"cutting open"the upper graphene from the defects to expose the lower ReSe2 using scanning tunneling microscopy(STM).From combination of these results with density functional theory calculations,the domain boundaries and edge sites of graphene are proposed to be adsorption sites for Re and Se precursors,further facilitating the growth of ReSe2 at the van der Waals gap of graphene/Au.This work hereby offers an intriguing strategy for obtaining vertical 2D heterostructures featured with an ultra-clean interface and a designed stacking geometry.

A universal etching-free transfer of MoS2 films for applications in photodetectors

从生长底层转移瞬间 2 电影到目标底层上是为他们的实际应用的一个关键问题。而且，避免样品降级和底层破坏仍然是大挑战，因为当前的转移方法不可避免地采用蚀刻的湿化学药品，处理。我们为由使用 ultrasonication 转移瞬间 2 电影到任意的底层上开发了一个蚀刻免费的转移方法。简短，在在聚合物涂的瞬间 2 之间的接口的产生 ultrasonication 的 microbubbles 的倒塌电影和底层导致足够的力量到 delaminate 瞬间 2 电影。用这个方法，瞬间 2 电影能从所有底层(硅石，云母，锶 titanate，和蓝宝石) 被转移并且保留原来的样品形态学和质量。这个方法保证一个简单转移过程并且允许生长底层的复用，没有包含任何危险蚀刻剂。蚀刻免费的转移方法是可能的在光电探测器支持瞬间 2 的宽广应用程序。

Mn atomic layers under inert covers of graphene and hexagonal boron nitride prepared on Rh（111）

Intercalation of metal atoms into the interface of graphene and its supporting substrate has become an intriguing topic for the sake of weakening the interface coupling and constructing metal atomic layers under inert covers. However, this novel behavior has rarely been reported on the analogous hexagonal boron nitride （h-BN） synthesized on metal substrates. Here, we describe a comparative study of Mn intercalation into the interfaces of graphene/Rh（111） and h-BN/Rh（111）, by using atomically-resolved scanning tunneling microscopy （STM） and density functional theory （DFT） calculations. The intercalation was performed by annealing as-deposited Mn clusters, and the starting temperature of Mn intercalation into h-BN/Rh（111） was found to be ~80 ~C higher than that for graphene/Rh（111）. Moreover, the intercalated islands of h-BN/Mn/Rh（111） usually possess more irregular shapes than those of graphene/Mn/Rh（111）, as illustrated by temperature-dependent STM observations. All these experimental facts suggest a stronger interaction of Mn with h-BN/Rh（111） than that with graphene/Rh（111）.

Transformation of monolayer MoS2 into multiphasic MoTe2： Chalcogen atom-exchange synthesis route

Molybdenum ditelluride （MoTe2）, which is an important transition-metal dichalcogenide, has attracted considerable interest owing to its unique properties, such as its small bandgap and large Seebeck coefficient. However, the batch production of monolayer MoTe2 has been rarely reported. In this study, we demonstrate the synthesis of large-domain （edge length exceeding 30 μm）, monolayer MoTe2 from chemical vapor deposition-grown monolayer MoS2 using a chalcogen atom-exchange synthesis route. An in-depth investigation of the tellurization process reveals that the substitution of S atoms by Te is prevalently initiated at the edges and grain boundaries of the monolayer MoS2, which differs from the homogeneous selenization of MoS2 flakes with the formation of alloyed Mo-S-Se hybrids. Moreover, we detect a large compressive strain （approximately -10%） in the transformed MoTe2 lattice, which possibly drives the phase transition from 2H to 1T＇ at the reaction temperature of 500 ℃. This phase change is substantiated by experimental facts and first-principles calculations. This work introduces a novel route for the templated synthesis of two-dimensional layered materials through atom substitutional chemistry and provides a new pathway for engineering the strain and thus the intriguing physics and chemistry.

Improving the device performances of two-dimensional semiconducting transition metal dichalcogenides: Three strategies

Two-dimensional(2D)semiconductors are emerging as promising candidates for the next-generation nanoelectronics.As a type of unique channel materials,2D semiconducting transition metal dichalcogenides(TMDCs),such as MoS2 and WS2,exhibit great potential for the state-of-the-art fieldeffect transistors owing to their atomically thin thicknesses,dangling-band free surfaces,and abundant band structures.Even so,the device performances of 2D semiconducting TMDCs are still failing to reach the theoretical values so far,which is attributed to the intrinsic defects,excessive doping,and daunting contacts between electrodes and channels.In this article,we review the up-to-date three strategies for improving the device performances of 2D semiconducting TMDCs:(i)the controllable synthesis of wafer-scale 2D semiconducting TMDCs single crystals to reduce the evolution of grain boundaries,(ii)the ingenious doping of 2D semiconducting TMDCs to modulate the band structures and suppress the impurity scatterings,and(iii)the optimization design of interfacial contacts between electrodes and channels to reduce the Schottky barrier heights and contact resistances.In the end,the challenges regarding the improvement of device performances of 2D semiconducting TMDCs are highlighted,and the further research directions are also proposed.We believe that this review is comprehensive and insightful for downscaling the electronic devices and extending the Moore’s law.

Quasi-freestanding, striped WS2 monolayer with an invariable band gap on Au（001）

Revealing the structural/electronic features and interfacial interactions of monolayer MoS2 and WS2 on metals is essential to evaluating the performance of related devices.In this study,we focused on the atomic-scale features of monolayer WS2 on Au（001） synthesized via chemical vapor deposition.Scanning tunneling microscopy and spectroscopy reveal that the WS2/Au（001） system exhibits a striped superstructure similar to that of MoS2/Au（001） but weaker interfacial interactions,as evidenced by experimental and theoretical investigations.Specifically,the WS2/Au（001） band gap exhibits a relatively intrinsic value of ～ 2.0 eV.However,the band gap can gradually decrease to ～ 1.5 eV when the sample annealing temperature increases from ～370 to 720 ℃.In addition,the doping level （or Fermi energy） of monolayer WS2/Au（001） varies little over the valley and ridge regions of the striped patterns because of the homogenous distributions of point defects introduced by annealing.Briefly,this work provides an in-depth investigation into the interfacial interactions and electronic properties of monolayer MX2 on metal substrates.

Controllability of surface plasmon polariton far-field radiation using a metasurface

In this study, a point-scattering approach to the plane-wave optical transmission of subwavelength metal nanoslit arrays with varying angles of rotation and that of subwavelength metal supercell arrays consisting of nanoslits capable of various angles of rotation is developed.It is demonstrated that the suggested theories show good agreement with the simulations and experiments. The results show that constructive and destructive interference at each nanoslit can respectively enhance and suppress the surface plasmon polariton (SPP) far-field radiation of a metasurface. The proposed theory can predict the quantity and resonant wavelength of SPPs and provide a design scheme for an SPP device.

Controlled Syntheses and Multifunctional Applications of Two-Dimensional Metallic Transition Metal Dichalcogenides

CONSPECTUS:Among two-dimensional(2D)layered materials,metallic transition metal dichalcogenides(MTMDCs)are emerging as promising candidates in many application aspects(e.g.,electronics,spintronics,and energy related fields,etc.)in view of their ultrahigh electronic conductivities,newfangled room-temperature ferromagnetism(e.g.,VSe_(2),VTe_(2)),and excellent catalytic activities.Specially,2D TaX_(2) and VX_(2)(X=S,Se,Te)materials stand in a vital place on account of their exotic physical and chemical properties.Notably,the controlled synthesis of such materials is the premise for exploring the aforementioned properties and applications.Among the reported preparation methods,chemical vapor deposition(CVD)is proven to be a promising approach in view of its scalability,simple operation,low cost,etc.This method has been employed to synthesize various 2D layered materials and heterostructures in a well-controlled fashion.Nevertheless,in view of the complicated growth mechanism and process,the CVD growth of ultrathin TaX_(2) and VX_(2) nanosheets/films remains extremely challenging.In addition,the application explorations of 2D TaX_(2) and VX_(2) in the energy related fields and electronic devices are still in the primary stage.In this Account,we review the up-to-date advances regarding the CVD syntheses of 2D TaX_(2) and VX_(2)(e.g.,TaS_(2),TaSe_(2),VS_(2),VSe_(2),and VTe_(2),etc.)and air-stable MTMDCs(e.g.,PtSe2,NiTe2),as well as their multifunctional applications in the energy related fields and electronic devices.First,the CVD growth of TaX_(2) and VX_(2) nanosheets/films with tunable thicknesses/domain sizes and the MTMDCs/semiconducting TMDCs vertical heterostructures are systematically summarized.Second,the application explorations of CVD-synthesized 2D TaX_(2) and VX_(2) as high-performance electrode materials in electrocatalytic hydrogen evolution reaction(HER)and electronic devices are introduced,respectively.Third,the CVD syntheses of 2D MTMDCs with robust environmental stability and novel physical properties(e.g.,semimetal−semiconductor transition,magnetism)are discussed.In the end,the challenges regarding the preparations and multifunctional applications of 2D MTMDCs are highlighted,and the future research directions are also proposed.We believe that this Account is comprehensive and insightful for the CVD syntheses of high-quality 2D MTMDCs materials toward versatile applications.