Topological superconductivity in Janus monolayer transition metal dichalcogenides

The Janus monolayer transition metal dichalcogenides(TMDs)MXY(M=Mo,W,etc.and X,Y=S,Se,etc.)have been successfully synthesized in recent years.The Rashba spin splitting in these compounds arises due to the breaking of out-of-plane mirror symmetry.Here we study the pairing symmetry of superconducting Janus monolayer TMDs within the weak-coupling framework near critical temperature Tc,of which the Fermi surface(FS)sheets centered around bothΓand K(K′)points.We find that the strong Rashba splitting produces two kinds of topological superconducting states which differ from that in its parent compounds.More specifically,at relatively high chemical potentials,we obtain a timereversal invariant s+f+p-wave mixed superconducting state,which is fully gapped and topologically nontrivial,i.e.,a Z_(2) topological state.On the other hand,a time-reversal symmetry breaking d+p+f-wave superconducting state appears at lower chemical potentials.This state possess a large Chern number|C|=6 at appropriate pairing strength,demonstrating its nontrivial band topology.Our results suggest the Janus monolayer TMDs to be a promising candidate for the intrinsic helical and chiral topological superconductors.

Interface engineering of transition metal dichalcogenide/GaN heterostructures:Modified broadband for photoelectronic performance

The GaN-based heterostructures are widely used in optoelectronic devices,but the complex surface reconstructions and lattice mismatch greatly limit the applications.The stacking of two-dimensional transition metal dichalcogenide(TMD=MoS_(2),MoSSe and MoSe_(2))monolayers on reconstructed GaN surface not only effectively overcomes the larger mismatch,but also brings about novel electronic and optical properties.By adopting the reconstructed GaN(0001)surface with adatoms(N-ter GaN and Ga-ter GaN),the influences of complicated surface conditions on the electronic properties of heterostructures have been investigated.The passivated N-ter and Ga-ter GaN surfaces push the mid-gap states to the valence bands,giving rise to small bandgaps in heterostructures.The charge transfer between Ga-ter GaN surface and TMD monolayers occurs much easier than that across the TMD/N-ter GaN interfaces,which induces stronger interfacial interaction and larger valence band offset(VBO).The band alignment can be switched between type-I and type-II by assembling different TMD monolayers,that is,MoS_(2)/N-ter GaN and MoS_(2)/Ga-ter GaN are type-II,and the others are type-I.The absorption of visible light is enhanced in all considered TMD/reconstructed GaN heterostructures.Additionally,MoSe_(2)/Ga-ter GaN and MoSSe/N-ter GaN have larger conductor band offset(CBO)of 1.32 eV and 1.29 eV,respectively,extending the range from deep ultraviolet to infrared regime.Our results revel that the TMD/reconstructed GaN heterostructures may be used for high-performance broadband photoelectronic devices.

Diverse atomic structure configurations of metal-doped transition metal dichalcogenides for enhancing hydrogen evolution

Doping foreign metal atoms into the substrate of transition metal dichalcogenides(TMDs)enables the formation of diverse atomic structure configurations,including isolated atoms,chains,and clusters.Therefore,it is very important to reasonably control the atomic structure and determine the structure-activity relationship between the atomic configurations and the hydrogen evolution reaction(HER)performance.Although numerous studies have indicated that doping can yield diverse atomic structure configurations,there remains an incomplete understanding of the relationship between atomic configurations within the lattice of TMDs and their performance.Here,diverse atomic structure configurations of adsorptive doping,substitutional doping,and TMDs alloys are summarized.The structure-activity relationship between different atomic configurations and HER performance can be determined by micro-nanostructure devices and density functional theory(DFT)calculations.These diverse atomic structure configurations are of great significance for activating the inert basal plane of TMDs and improving the catalytic activity of HER.Finally,we have summarized the current challenges and future opportunities,offering new perspectives for the design of highly active and stable metal-doped TMDs catalysts.

Exfoliation,functionalization and antibacterial activity of transition metal dichalcogenides

Due to the growing resistance of available drugs to bacterial infection and the slow development of antibiotics,there is a continuous need to design and develop new antibacterial agents.The interest to develop transition metal dichalcogenides(TMDs)based antibacterial agents has significantly increased in recent years.This research interest is driven by their interesting properties such as metallic and semiconducting nature of different phases,electronic confinement,large surface to volume ratio,the possibility of surface functionalization,and their potential application as a material in biomedical sciences.Different synthetic strategies have been developed to synthesize monolayered TMDs and their functionalization with different bioactive molecules.Researchers have given a lot of effort to establish the structure-activity correlation between different TMDs and their antibacterial activity.Here,we have reviewed various exfoliation strategies for TMDs,different methods for their functionalization,and the antibacterial activity of different TMDs.

过渡金属硫族化合物激子研究进展

分别介绍了激子的基本概念及过渡金属硫族化合物(transition metal dichalcogenides,TMD)材料中不同类型的激子态,并对TMD材料中激子的调控方法和手段进行了系统综述;总结了TMD材料中激子问题的潜在研究方向及应用.

Recent developments in CVD growth and applications of 2D transition metal dichalcogenides

Two-dimensional(2D)transition metal dichalcogenides(TMDs)with fascinating electronic energy band structures,rich valley physical properties and strong spin–orbit coupling have attracted tremendous interest,and show great potential in electronic,optoelectronic,spintronic and valleytronic fields.Stacking 2D TMDs have provided unprecedented opportunities for constructing artificial functional structures.Due to the low cost,high yield and industrial compatibility,chemical vapor deposition(CVD)is regarded as one of the most promising growth strategies to obtain high-quality and large-area 2D TMDs and heterostructures.Here,state-of-the-art strategies for preparing TMDs details of growth control and related heterostructures construction via CVD method are reviewed and discussed,including wafer-scale synthesis,phase transition,doping,alloy and stacking engineering.Meanwhile,recent progress on the application of multi-functional devices is highlighted based on 2D TMDs.Finally,challenges and prospects are proposed for the practical device applications of 2D TMDs.

MoS_(2)和MoTe_(2)同质结和异质结中的表面电势排列

过渡金属硫族化合物(TMD)薄层仅改变几何形状(如层厚)就可调节带隙、电子亲和势和费米能级,使器件设计更灵活。但因缺乏费米能级排列信息,TMD同质/异质结器件常因未知的能带弯曲而偏离预期。利用扫描开尔文探针显微镜(SKPM)表征了TMD同质/异质结,结果显示,Mo S_(2)和Mo Te_(2)同质结的费米能级随层厚增加向本征费米能级移动(背景掺杂浓度降低),而Mo Te_(2)/Mo S_(2)异质结中探测到宽耗尽区和强光响应,同时给出表面污染(分子尺度)对单层TMD表面电势的影响。上述发现将在器件设计中帮助精准堆叠范德华(vdW)层。

纳米过渡金属硫化物在摩擦学应用中的研究进展

介绍了过渡层状金属硫化物MX2(M=Mo、W;X=S、Se)的结构和独特的性质,综述了无机类富勒烯过渡金属硫化物纳米材料的摩擦学研究现状和近年来的研究成果。通过对包括纳米颗粒、纳米薄膜在内的纳米硫化物摩擦性能研究的介绍,评述了纳米金属硫化物的抗磨减摩机制,如滚动滑动摩擦机制、化学反应、第三体等,并对纳米摩擦学的表征方法和研究手段进行了总结。最后展望了纳米过渡层状金属硫化物在摩擦学应用中存在的问题及发展趋势。

二硫化铌纳米线作为润滑油添加剂的摩擦学性能研究

通过固相沉积法合成了一维硫化铌纳米材料,用透射电子显微镜表征了该一维纳米材料的形貌特征。将硫化铌纳米线作为润滑油添加剂,按不同质量分数配比,用MS-T3000摩擦试验机评价了其摩擦性能,探讨了含硫化铌纳米材料润滑油的摩擦机制。结果表明,在低载荷时,含有NbS2添加剂的润滑油并没有优势,在高载荷时可以有效减小摩擦因数;单独增加添加剂质量分数,不能相应减小摩擦磨损,且在低载荷时,摩擦因数还会随质量分数的增加而变大,但在高载荷时,随着NbS2质量分数的增加,摩擦因数减小。添加剂有利于提高润滑油的承载能力,其优异的承载能力可能归结于3个方面:独特的闭合结构、润滑膜转移机制和填充条件修复机制。

基于CVD单层MoS_2 FET的光电探测器

通过化学气相沉积(CVD)工艺在SiO_2/Si衬底生长出MoS_2材料,对材料进行喇曼光谱表征,验证了单层MoS_2的存在;基于CVD生长的单层MoS_2完成了晶圆级背栅场效应晶体管(FET)光电探测器的工艺研发;对MoS_2 FET器件进行了电学特性表征,开关比可达到105数量级,场效应迁移率约为1 cm2·V-1·s-1,栅极漏电流为10-10 A数量级;对MoS2FET器件的光电特性进行了表征,该光电探测器具有普通光电导探测器的基本光电特性,其光电流随光照强度的增强以及源漏电压的增加而增加,同时由于栅极的调制提高了光电探测器的灵活性。通过控制栅极电压能够控制MoS2FET光电探测器的暗电流大小,实现对探测器η参数的有效调制。最后通过器件能带图对MoS_2 FET光电探测器的光电特性进行了阐释,为其走向实际应用奠定了理论基础。

用于FET的PECVD SiN_x掺杂MoS_2的有效性与可控性

通过化学气相沉积(CVD)工艺成功生长出少层MoS_2薄膜,用Raman光谱仪对材料进行表征,验证了三层MoS_2材料的存在。基于CVD生长出的三层MoS_2薄膜材料完成了背栅场效应晶体管(FET)的制作工艺研发。对MoS_2FET器件进行了电学特性表征,研制的MoS_2FET器件的开关比可达到1.45×10~6,器件的电子载流子场效应迁移率约为1 cm^2·V^(-1)·s^(-1)。对等离子增强化学气相沉积(PECVD)氮化硅(SiN_x)工艺掺杂MoS_2材料进行了研究,掺杂后器件的驱动电流提高了3倍多,验证了SiN_x掺杂MoS_2材料的有效性。通过控制PECVD SiN_x时间工艺参数对SiN_x薄膜厚度与掺杂浓度的关系进行了研究,随着SiN_x薄膜厚度增加器件的驱动电流逐渐增强,验证了SiN_x掺杂MoS_2材料的可控性。最后,对PECVD SiN_x工艺掺杂MoS_2材料的机理进行了讨论。

二维WSe_(2)场效应晶体管光电性能

自石墨烯被发现以来,随着人们不断的研究和探索,越来越多具有类似结构的二维材料因其优异的光电性质相继被发现和研究。过渡金属硫族化合物(TMDs)因其丰富的物理性质而受到广泛关注。本文研究了三层二硒化钨(WSe_(2))纳米片的光电性能。利用范德华力将WSe_(2)转移到SiO_(2)/Si衬底的Au电极上,用银浆引出背栅电极,制备了WSe_(2)场效应晶体管,其载流子迁移率为3.42 cm^(2)/(V·s)。WSe_(2)场效应晶体管在630 nm波长下探测器响应度为0.61 A/W,器件的光响应恢复时间为1900 ms。

过渡金属硫族化合物二维晶体基复合材料的研究进展

石墨烯的发现掀起了人们对二维晶体材料的探索热潮。单层或少数层过渡金属硫族化合物(TMDs)是二维晶体材料的典型代表,此类材料的带隙合适、电子迁移率和热导率高、光吸收强、比表面积大,在新型光电器件、光/电催化、锂离子电池电极、气体传感及生物医学等领域蕴藏着巨大的应用潜能。特别是,对于TMDs二维晶体与其他材料复合而成的纳米结构,强烈的界面耦合作用对材料物理和化学特性的调控至关重要,甚至可能导致新奇特性,预示着新功能和新应用。详细综述了TMDs二维晶体基复合材料的制备方法、结构与性能的界面调控及其潜在应用,并指出了该研究领域仍存在的问题及未来发展方向。

基于二维半导体的模拟电路最新进展

摩尔定律驱动的器件持续微缩已经开始给硅基晶体管的模拟性能带来潜在问题,其中本征增益作为最重要的模拟指标会随着技术节点的缩小而降低。二维半导体因其平坦的界面、原子级厚度的几何结构,允许极好的栅静电控制,并且不受短通道效应的影响而引起了广泛的关注。这些优异的特性使二维半导体在提高模拟电路性能中表现出巨大的潜力。本文中,我们回顾了基于二维半导体的模拟电路的最新研究进展。文章首先介绍了衡量模拟电路性能的重要指标,然后重点介绍了基于二维半导体的单级放大器的实现、接触工程、和互补技术,并进一步讨论了基于二维晶体管的复杂电路,如电流镜、运算放大器、射频电路。最后我们讨论了基于二维晶体管的模拟电路的应用前景和面临的关键挑战。

过渡金属二硫化物在能量转换与存储上的应用

过渡金属二硫化物(TMDs)具有与石墨类似的层状结构,因其具有独特的物理和化学性质,在能源领域显示出巨大的应用潜力,已经引起了人们广泛的关注。本文综述了层状TMDs的结构特征、基本性质和常用的合成方法,重点介绍了其在能源转换和存储领域的典型应用,包括在太阳能电池方面的应用,在电催化方面的应用,在超级电容器方面的应用以及在硫锂电池方面的应用。最后对层状TMDs的发展趋势进行了展望。

Valleytronics in transition metal dichalcogenides materials

Valley degree of freedom in the first Brillouin zone of Bloch electrons offers an innovative approach to information storage and quantum computation.Broken inversion symmetry together with the presence of time-reversal symmetry endows Bloch electrons non-zero Berry curvature and orbital magnetic moment,which contribute to the valley Hall effect and optical selection rules in valleytronics.Furthermore,the emerging transition metal dichalcogenides(TMDs)materials naturally become the ideal candidates for valleytronics research attributable to their novel structural,photonic and electronic properties,especially the direct bandgap and broken inversion symmetry in the monolayer.However,the mechanism of inter-valley relaxation remains ambiguous and the complicated manipulation of valley predominantly incumbers the realization of valleytronic devices.In this review,we systematically demonstrate the fundamental properties and tuning strategies(optical,electrical,magnetic and mechanical tuning)of valley degree of freedom,summarize the recent progress of TMD-based valleytronic devices.We also highlight the conclusion of present challenges as well as the perspective on the further investigations in valleytronics.

基于TMD材料的CMOS反相器电路研究现状

对目前基于过渡金属硫族化合物(TMD)材料(MoS_(2)、WSe_(2)等)的互补金属氧化物半导体(CMOS)反相器电路相关研究进行了综述。总结了TMD材料的物理性质、制备方法和基于TMD的场效应晶体管器件的研究进展。对基于TMD的集成电路技术研究进行了介绍与分析。分别在结构设计、集成工艺、性能优化及电路集成等方面对基于TMD材料的CMOS反相器电路进行了总结与分析。介绍了两种集成结构及对应的工艺流程,详细分析了CMOS反相器电路性能优化的方法。最后指出了目前的关键挑战及未来的发展趋势。

Two-dimensional noble transition-metal dichalcogenides for nanophotonics and optoelectronics:Status and prospects

An emerging subclass of transition-metal dichalcogenides(TMDs),noble-transition-metal dichalcogenides(NMDs),has led to an increase in nanoscientific research in two-dimensional(2D)materials.NMDs feature a unique structure and several useful properties.2D NMDs are promising candidates for a broad range of applications in areas such as photodetectors,phototransistors,saturable absorbers,and meta optics.In this review,the state of the art of 2D NMDs research,their structures,properties,synthesis,and potential applications are discussed,and a perspective of expected future developments is provided.

Visible-to-near-infrared photodetector based on graphene–MoTe2–graphene heterostructure

Graphene and transition metal dichalcogenides(TMDs), two-dimensional materials, have been investigated wildely in recent years. As a member of the TMD family, MoTe2 possesses a suitable bandgap of ~1.0 eV for near infrared(NIR)photodetection. Here we stack the MoTe2 flake with two graphene flakes of high carrier mobility to form a graphene–MoTe2–graphene heterostructure. It exhibits high photo-response to a broad spectrum range from 500 nm to 1300 nm. The photoresponsivity is calculated to be 1.6 A/W for the 750-nm light under 2 V/0 V drain–source/gate bias, and 154 mA/W for the 1100-nm light under 0.5 V/60 V drain–source/gate bias. Besides, the polarity of the photocurrent under zero Vds can be efficiently tuned by the back gate voltage to satisfy different applications. Finally, we fabricate a vertical graphene–MoTe2–graphene heterostructure which shows improved photoresponsivity of 3.3 A/W to visible light.

Topological structures of transition metal dichalcogenides: A review on fabrication, effects, applications, and potential

Transition metal dichalcogenides(TMDs)have received tremendous attention owing to their potential for optoelectronic applications.Topological structures,such as wrinkles,folds,and scrolls,have been generated on TMDs,thereby exhibiting novel physical properties with improved optoelectronic performance,making them attractive prospects for both basic understanding and advanced applications in optoelectronics.In this review,the methods for fabricating wrinkles,folds,and scrolls on TMDs are outlined,including modification of the fabrication and transfer processes,and manipulation via auxiliary polymers.The effects on their physical and electronic properties are also discussed,with particular paid to the energy band structure,single-photon sources,second harmonic generation(SHG),and interlayer coupling.In comparison to pristine TMDs,these topologies exhibit great advantages in optoelectronic devices,such as field-effect transistors and photodetectors.Finally,existing challenges and opportunities of wrinkled,folded,and scrolled TMDs are outlined and an outlook is presented.