Growing Biomorphic Transition Metal Dichalcogenides and Their Alloys Toward High Permeable Membranes and Efficient Electrocatalysts Applications

3D architecratured transition metal dichalcogenides constructed by atomically thin layers are appealing building blocks in various applications,such as catalysts,energy storage,conversions,sensors,and so on.However,the direct growth of 3D transition metal dichalcogenides architectures with high crystal quality and well-controlled size/thickness remains a huge challenge.Herein,we report a facile,highly-repeatable,and versatile chemical vapor deposition strategy,for the mass production of high-quality 3D-architecratured transition metal dichalcogenides(e.g.,MoS_(2),WS_(2),and ReS_(2))and their alloys(e.g.,W_(x)Mo(1–x)S_(2)and Rex Mo_((1–x))S_(2))nanosheets on naturally abundant and low-cost diatomite templates.Particularly,the purified transition metal dichalcogenides products exhibit unique and designable 3D biomorphic hierarchical microstructures,controllable layer thicknesses,tailorable chemical compositions,and good crystallinities.The weak interlayer interactions endow them with good dispersity in solutions to form stable additive-free inks for solution-processing-based applications,for example,high-permeable and high-stable separation membranes for water purification,and efficient electrocatalysts for hydrogen evolution reactions.This work paves ways for the low-cost,mass production of versatile transition metal dichalcogenides powder-like materials with designable structures and properties,toward energy/environmental-related applications and beyond.

面向电极接触应用的二维金属性过渡金属硫属化合物的制备和器件研究进展

二维(two-dimensional,2D)层状半导体材料因具有原子级厚度、优异的光电性质和良好的热/化学稳定性等,被认为是延续摩尔定律的重要候选材料之一.基于超薄2D半导体材料构建的电子器件本质上是一种界面器件,其性能与金属-半导体接触的质量密切相关.常规蒸镀法制备金属电极通常涉及高能原子(团簇)轰击,该过程往往导致沟道材料的损伤和界面缺陷的产生,使得接触质量下降,接触电阻增大,器件性能显著恶化.2D金属性过渡金属硫属化合物(metallic transition metal dichalcogenides,MTMDCs)和半导体性TMDCs具有类似的材料组成、相同的层间范德华相互作用、可兼容的制备方法等,有望作为金属-半导体接触的界面材料,有效改善接触问题.目前,面向电极接触应用的高质量2D-MTMDCs的制备与应用已取得重要进展.本文综述了近年来基于化学气相沉积(chemical vapor deposition,CVD)法制备MTMDCs的一些研究成果,包括不同材料体系的制备、结构表征以及作为电极接触的应用等,最后讨论了该领域目前存在的问题,展望了未来可能的发展方向.

二维金属性过渡金属硫属化合物的可控制备和潜在应用

二维金属性过渡金属硫属化合物(metal transition metal dichalcogenides,MTMDCs)由于其独特的物性(如电荷密度波相转变、超导和磁性等),以及在先进纳米电子学和能源相关领域的应用潜力而受到研究者的广泛关注.为了实现基本物性研究和多方面的应用探索,化学气相沉积(CVD)技术被引入到高质量二维MTMDCs材料的制备中,成功地合成了厚度可调的超薄MTMDCs纳米片、大面积均匀的超薄薄膜、垂直取向的纳米片阵列和高质量的纳米片粉体等.CVD方法可以兼顾大畴区、层厚可调和高晶体质量的材料制备需求,还能与目前的半导体工艺相兼容,因而受到人们广泛关注.二维MTMDCs材料具有高的电导率,可以作为单层/少层半导体性过渡金属硫属化合物(transition metal dichalcogenides,TMDCs)的电极材料,改善晶体管器件的电极接触,从而提升器件性能.此外,二维MTMDCs纳米片也可作为高效的催化剂应用于电化学析氢反应,其催化性能显著优于单层/少层MoS2等半导体性TMDCs催化剂.本文综述了二维MTMDCs材料的CVD制备方法和新奇物理特性,以及其在场效应晶体管、电催化析氢应用中的研究进展;最后讨论了相关领域存在的问题和未来发展方向.

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.

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.

Scalable salt-templated directed synthesis of high-quality MoS_(2) nanosheets powders towards energetic and environmental applications

Two-dimensional(2D)transition metal dichalcogenides(TMDCs)have emerged as perfect platforms for developing applications in nano-electronics,catalysis,energy storage and environmental-related fields due to their superior properties.However,the low-cost,batch production of high-quality 2D TMDCs remains a huge challenge with the existing synthetic strategies.Herein,we present a scalable chemical vapor deposition(CVD)approach for the batch production of high-quality MoS_(2) nanosheet powders,by using naturally abundant,water-soluble and recyclable NaCl crystal powders as templates.The high-quality MoS_(2) nanosheets powders are achieved by a facile water dissolution-filtration process,by virtue of the excellent dispersibility of the as-grown products in water.The internal mechanism for the scalable synthesis strategy is explored.The applications of the MoS_(2) nanosheets powders are also demonstrated as catalysts or adsorbents in hydrogen evolution reaction(HER)and organic dyes adsorption,respectively.This work should hereby pave ways for the mass production and application of powdery TMDCs in energetic and environmental related fields.

Salt-assisted growth and ultrafast photocarrier dynamics of large-sized monolayer ReSe2

Owing to its anisotropic optical and electrical properties,rhenium diselenide(ReSe2)has garnered considerable attention recently as a candidate material for polarization-sensitive photodetectors.However,the direct and controllable synthesis of large-sized ReSe2 with a uniform thickness is still a great challenge.Herein,we have refined the synthesis method to obtain uniform monolayer ReSe2 flakes with a size of up to^106μm on sapphire via an ambient-pressure chemical vapor deposition technique using Na promoter from sodium chloride.Interestingly,optical pump-probe spectroscopy revealed a fast switching from saturable absorption(SA)to absorption enhancement(AE)in subpicosecond time scale,followed by a slower decay induced by exciton recombination.Furthermore,both AE and SA signals exhibited clear angular dependence with a periodicity of 180°,which reflected the dichroism in nonlinear absorption dynamics.In addition,the photocarrier dynamics including free-carrier transport and subpicosecond relaxation due to exciton formation or surface trapping was probed using time resolved terahertz spectroscopy.We believe that our study serves as a reference for atomically controlled synthesis of large-sized ReSe2 and provides useful insights on its optoelectronic properties for novel device applications.

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.

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.