Thermoelectric generators have attracted a wide research interest owing to their ability to directly convert heat into electrical power.Moreover,the thermoelectric properties of traditional inorganic and organic mater...Thermoelectric generators have attracted a wide research interest owing to their ability to directly convert heat into electrical power.Moreover,the thermoelectric properties of traditional inorganic and organic materials have been significantly improved over the past few decades.Among these compounds,layered two-dimensional(2D)materials,such as graphene,black phosphorus,transition metal dichalcogenides,IVA–VIA compounds,and MXenes,have generated a large research attention as a group of potentially high-performance thermoelectric materials.Due to their unique electronic,mechanical,thermal,and optoelectronic properties,thermoelectric devices based on such materials can be applied in a variety of applications.Herein,a comprehensive review on the development of 2D materials for thermoelectric applications,as well as theoretical simulations and experimental preparation,is presented.In addition,nanodevice and new applications of 2D thermoelectric materials are also introduced.At last,current challenges are discussed and several prospects in this field are proposed.展开更多
Two-dimensional(2D) materials with atomic thickness are promising candidates for the applications in future semiconductor devices, owing to their fascinating physical properties and superlative optoelectronic performa...Two-dimensional(2D) materials with atomic thickness are promising candidates for the applications in future semiconductor devices, owing to their fascinating physical properties and superlative optoelectronic performance. Chemical vapor deposition(CVD) is considered to be an efficient method for large-scale preparation of 2D materials toward practical applications.However, the high melting points of metal precursors and the thermodynamics instabilities of metastable phases limit the direct CVD synthesis of plenty of 2D materials. The salt has recently been introduced into the CVD process, which proved to be effective to address these issues. In this review, we highlighted the latest progress in the salt-assisted CVD growth of 2D materials, including layered and non-layered crystals. Firstly, strategies of adding salts are summarized. Then, the salt-assisted growth of various layered materials is presented, emphasizing on the transition metal chalcogenides of stable and metastable phases. Furthermore, strategies to grow ultrathin non-layered materials are discussed. We provide viewpoints into the techniques of using salt, the effects of salt, and the growth mechanisms of 2D crystals. Finally, we offer the challenges to be overcome and further research directions of this emerging salt-assisted CVD technique.展开更多
Intensive research effort is currently focused on the development of efficient, reliable, and environmentally safe electrochemical energy storage systems due to the ever-increasing global energy storage demand. Li ion...Intensive research effort is currently focused on the development of efficient, reliable, and environmentally safe electrochemical energy storage systems due to the ever-increasing global energy storage demand. Li ion battery systems have been used as the primary energy storage device over the last three decades. However, low abundance and uneven distribution of lithium and cobalt in the earth crust and the associated cost of these materials, have resulted in a concerted effort to develop beyond lithium electrochemical storage systems. In the case of non-Li ion rechargeable systems, the development of electrode materials is a significant challenge, considering the larger ionic size of the metal-ions and slower kinetics. Two-dimensional(2D) materials, such as graphene, transition metal dichalcogenides, MXenes and phosphorene, have garnered significant attention recently due to their multi-faceted advantageous properties: large surface areas, high electrical and thermal conductivity, mechanical strength, etc. Consequently, the study of 2D materials as negative electrodes is of notable importance as emerging non-Li battery systems continue to generate increasing attention. Among these interesting materials, graphene has already been extensively studied and reviewed, hence this report focuses on 2D materials beyond graphene for emerging non-Li systems. We provide a comparative analysis of 2D material chemistry, structure, and performance parameters as anode materials in rechargeable batteries and supercapacitors.展开更多
Two-dimensional group-VIB transition metal dichalcogenides（with the formula of MX2） emerge as a family of intensely investigated semiconductors that are promising for both electronic（because of their reasonable car...Two-dimensional group-VIB transition metal dichalcogenides（with the formula of MX2） emerge as a family of intensely investigated semiconductors that are promising for both electronic（because of their reasonable carrier mobility） and optoelectronic（because of their direct band gap at monolayer thickness） applications. Effective mass is a crucial physical quantity determining carriers transport, and thus the performance of these applications. Here we present based on first-principles high-throughput calculations a computational study of carrier effective masses of the two-dimensional MX2 materials. Both electron and hole effective masses of different MX2（M = Mo, W and X = S, Se, Te）, including in-layer/out-of-layer components, thickness dependence, and magnitude variation in heterostructures, are systemically calculated. The numerical results, chemical trends, and the insights gained provide useful guidance for understanding the key factors controlling carrier effective masses in the MX2 system and further engineering the mass values to improve device performance.展开更多
Ternary transition metal dichalcogenide alloys with spatially graded bandgaps are an emerging class of two-dimensional materials with unique features,which opens up new potential for device applications.Here,visible–...Ternary transition metal dichalcogenide alloys with spatially graded bandgaps are an emerging class of two-dimensional materials with unique features,which opens up new potential for device applications.Here,visible–near-infrared and self-powered phototransistors based on spatially bandgap-graded MoS2(1−x)Se2x alloys,synthesized by a simple and controllable chemical solution deposition method,are reported.The graded bandgaps,arising from the spatial grading of Se composition and thickness within a single domain,are tuned from 1.83 to 1.73 eV,leading to the formation of a homojunction with a builtin electric field.Consequently,a strong and sensitive gate-modulated photovoltaic effect is demonstrated,enabling the homojunction phototransistors at zero bias to deliver a photoresponsivity of 311 mA W−1,a specific detectivity up to^10^11 Jones,and an on/off ratio up to^10^4.Remarkably,when illuminated by the lights ranging from 405 to 808 nm,the biased devices yield a champion photoresponsivity of 191.5 A W−1,a specific detectivity up to^1012 Jones,a photoconductive gain of 10^6–10^7,and a photoresponsive time in the order of^50 ms.These results provide a simple and competitive solution to the bandgap engineering of two-dimensional materials for device applications without the need for p–n junctions.展开更多
First-principle calculations with different exchange-correlation functionals, including LDA, PBE, and vd W-DF functional in the form of opt B88-vd W, have been performed to investigate the electronic and elastic prope...First-principle calculations with different exchange-correlation functionals, including LDA, PBE, and vd W-DF functional in the form of opt B88-vd W, have been performed to investigate the electronic and elastic properties of twodimensional transition metal dichalcogenides（TMDCs） with the formula of MX2（M = Mo, W; X = O, S, Se, Te） in both monolayer and bilayer structures. The calculated band structures show a direct band gap for monolayer TMDCs at the K point except for MoO2 and WO2. When the monolayers are stacked into a bilayer, the reduced indirect band gaps are found except for bilayer WTe2, in which the direct gap is still present at the K point. The calculated in-plane Young moduli are comparable to that of graphene, which promises possible application of TMDCs in future flexible and stretchable electronic devices. We also evaluated the performance of different functionals including LDA, PBE, and opt B88-vd W in describing elastic moduli of TMDCs and found that LDA seems to be the most qualified method. Moreover, our calculations suggest that the Young moduli for bilayers are insensitive to stacking orders and the mechanical coupling between monolayers seems to be negligible.展开更多
Newborn two-dimensional materials(NB2DMs) beyond graphene such as transition metal dichalcogenides(TMDs) exhibit excellent optoelectronic and mechanical properties as well as high theoretical specific capacity, which ...Newborn two-dimensional materials(NB2DMs) beyond graphene such as transition metal dichalcogenides(TMDs) exhibit excellent optoelectronic and mechanical properties as well as high theoretical specific capacity, which make them become the promising building blocks of flexible energy devices related to energy conversion and storage. Compared to graphene with zero band gap or traditional friable materials such as Si, these NB2 DMs are more suitable to construct flexible devices as active layers of optoelectronic devices or as active materials for batteries. The present review focuses on the recent advances in bendable energy devices based on NB2 DMs, including batteries, supercapacitors(SCs), solar cells, photodetectors and nanogenerators(NGs). The NB2 DMs pave a new way to construct next-generation flexible energy devices with improved performance and we believe that those devices will be seen in our daily life and change our lifestyle in the immediate future.展开更多
过渡金属二硫化物(Transition Metal Dichalcogenides,TMDs)以其优异的光电子学特性,在诸如光捕获、光电探测、光电晶体管、发光二极管以及纳米激光器等领域中展现出了强大的应用潜力,成为当前研究前沿热点之一.少层TMDs材料的带隙处于...过渡金属二硫化物(Transition Metal Dichalcogenides,TMDs)以其优异的光电子学特性,在诸如光捕获、光电探测、光电晶体管、发光二极管以及纳米激光器等领域中展现出了强大的应用潜力,成为当前研究前沿热点之一.少层TMDs材料的带隙处于可见和近红外区间,其激子在室温下具有很大的束缚能、高谐振子强度,且单层TMDs由于空间反演对称性的破缺具有能谷选择的圆二色性等,这些特性使得TMDs材料格外引人注目.金属纳米结构的表面等离激元具有亚波长的光局域特性,可通过合理的结构设计实现对其共振波长、频谱宽度、近场增强倍数、远场辐射特性的灵活控制.将等离激元光学结构和过渡金属二硫化物相结合可大幅拓宽纳米光子学前沿基础问题研究与纳米光电器件的设计应用.本文综述了表面等离激元和TMDs材料复合体系的最新研究进展,着重阐述了为何这类复合体系能够提供他们各自体系所不能具有的特性.比如,表面等离激元的近场增强(场局域)效应可极大增强许多纳米光学系统中的光与物质相互作用强度,可用于对TMDs材料的光吸收、光发射、光电流以及非线性光学等过程进行调制.TMDs材料具备的受外界环境调控的强激子效应和能谷选择的圆二色性等特性,可为表面等离激元纳米结构提供丰富的主动调制手段与能谷自由度.最后展望了该新型复合体系未来的研究方向和机遇.展开更多
Transition metal dichalcogenides （TMDCs） have gained considerable attention because of their novel properties and great potential applications. The flakes of TMDCs not only have great light absorption from visible t...Transition metal dichalcogenides （TMDCs） have gained considerable attention because of their novel properties and great potential applications. The flakes of TMDCs not only have great light absorption from visible to near infrared, but also can be stacked together regardless of lattice mismatch like other two-dimensional （2D） materials. Along with the studies on intrinsic properties of TMDCs, the junctions based on TMDCs become more and more important in applications of photodetection. The junctions have shown many exciting possibilities to fully combine the advantages of TMDCs, other 2D materials, conventional and organic semiconductors together. Early studies have greatly enriched the application of TMDCs in photodetection. In this review, we investigate the efforts in photodetectors based on the junctions of TMDCs and analyze the properties of those photodetectors. Homojunctions based on TMDCs can be made by surface chemical doping, elemental doping and electrostatic gating. Heterojunction formed between TMDCs/2D materials, TMDCs/conventional semiconductors and TMDCs/organic semiconductor also deserve more attentions. We also compare the advantages and disadvantages of different junctions, and then give the prospects for the development of junctions based on TMDCs.展开更多
The explosion of interest in two-dimensional van der Waals materials has been in many ways driven by their layered geometry. This feature makes possible numerous avenues for assembling and ma- nipulating the optical a...The explosion of interest in two-dimensional van der Waals materials has been in many ways driven by their layered geometry. This feature makes possible numerous avenues for assembling and ma- nipulating the optical and electronic properties of these materials. In the specific case of monolayer transition metal dichalcogenide semiconductors, the direct band gap combined with the flexibility for manipulation of layers has made this class of materials promising for optoelectronics. Here, we review the properties of these layered materials and the various means of engineering these properties for optoeleetronics. We summarize approaches for control that modify their structural and chemical en- vironment, and we give particular detail on the integration of these materials into engineered optical fields to control their optical characteristics. This combination of controllability from their layered surface structure and photonic environment provide an expansive landscape for novel optoelectronic phenomena.展开更多
基金supported by National Science Foundation for Young Scientists of China (No.61905161 and 51702219)the National Natural Science Foundation of China (No.61975134,61875138 and 61775147)+1 种基金the Science and Technology Innovation Commission of Shenzhen (No. JCYJ20180206121837007)the Shenzhen Nanshan District Pilotage Team Program (LHTD20170006)
文摘Thermoelectric generators have attracted a wide research interest owing to their ability to directly convert heat into electrical power.Moreover,the thermoelectric properties of traditional inorganic and organic materials have been significantly improved over the past few decades.Among these compounds,layered two-dimensional(2D)materials,such as graphene,black phosphorus,transition metal dichalcogenides,IVA–VIA compounds,and MXenes,have generated a large research attention as a group of potentially high-performance thermoelectric materials.Due to their unique electronic,mechanical,thermal,and optoelectronic properties,thermoelectric devices based on such materials can be applied in a variety of applications.Herein,a comprehensive review on the development of 2D materials for thermoelectric applications,as well as theoretical simulations and experimental preparation,is presented.In addition,nanodevice and new applications of 2D thermoelectric materials are also introduced.At last,current challenges are discussed and several prospects in this field are proposed.
基金supported by the National Natural Science Foundation of China (21825103, 51727809)the Fundamental Research Funds for the Central University (2019kfy XMBZ018)the project funded by China Postdoctoral Science Foundation (2018M642832)
文摘Two-dimensional(2D) materials with atomic thickness are promising candidates for the applications in future semiconductor devices, owing to their fascinating physical properties and superlative optoelectronic performance. Chemical vapor deposition(CVD) is considered to be an efficient method for large-scale preparation of 2D materials toward practical applications.However, the high melting points of metal precursors and the thermodynamics instabilities of metastable phases limit the direct CVD synthesis of plenty of 2D materials. The salt has recently been introduced into the CVD process, which proved to be effective to address these issues. In this review, we highlighted the latest progress in the salt-assisted CVD growth of 2D materials, including layered and non-layered crystals. Firstly, strategies of adding salts are summarized. Then, the salt-assisted growth of various layered materials is presented, emphasizing on the transition metal chalcogenides of stable and metastable phases. Furthermore, strategies to grow ultrathin non-layered materials are discussed. We provide viewpoints into the techniques of using salt, the effects of salt, and the growth mechanisms of 2D crystals. Finally, we offer the challenges to be overcome and further research directions of this emerging salt-assisted CVD technique.
基金supported by the National Science Foundation Grant Number 1454151
文摘Intensive research effort is currently focused on the development of efficient, reliable, and environmentally safe electrochemical energy storage systems due to the ever-increasing global energy storage demand. Li ion battery systems have been used as the primary energy storage device over the last three decades. However, low abundance and uneven distribution of lithium and cobalt in the earth crust and the associated cost of these materials, have resulted in a concerted effort to develop beyond lithium electrochemical storage systems. In the case of non-Li ion rechargeable systems, the development of electrode materials is a significant challenge, considering the larger ionic size of the metal-ions and slower kinetics. Two-dimensional(2D) materials, such as graphene, transition metal dichalcogenides, MXenes and phosphorene, have garnered significant attention recently due to their multi-faceted advantageous properties: large surface areas, high electrical and thermal conductivity, mechanical strength, etc. Consequently, the study of 2D materials as negative electrodes is of notable importance as emerging non-Li battery systems continue to generate increasing attention. Among these interesting materials, graphene has already been extensively studied and reviewed, hence this report focuses on 2D materials beyond graphene for emerging non-Li systems. We provide a comparative analysis of 2D material chemistry, structure, and performance parameters as anode materials in rechargeable batteries and supercapacitors.
基金Project supported by the National Natural Science Foundation of China(Nos.11404131,11674121)the Program for JLU Science and Technology Innovative Research Teamthe Special Fund for Talent Exploitation in Jilin Province of China
文摘Two-dimensional group-VIB transition metal dichalcogenides（with the formula of MX2） emerge as a family of intensely investigated semiconductors that are promising for both electronic（because of their reasonable carrier mobility） and optoelectronic（because of their direct band gap at monolayer thickness） applications. Effective mass is a crucial physical quantity determining carriers transport, and thus the performance of these applications. Here we present based on first-principles high-throughput calculations a computational study of carrier effective masses of the two-dimensional MX2 materials. Both electron and hole effective masses of different MX2（M = Mo, W and X = S, Se, Te）, including in-layer/out-of-layer components, thickness dependence, and magnitude variation in heterostructures, are systemically calculated. The numerical results, chemical trends, and the insights gained provide useful guidance for understanding the key factors controlling carrier effective masses in the MX2 system and further engineering the mass values to improve device performance.
基金supported by Grants from the UK EPSRC Future Compound Semiconductor Manufacturing Hub(EP/P006973/1)the financial support from EPSRC(EP/L018330/1,EP/N032888/1)+3 种基金the U.S.Army Research Laboratory under Cooperative Agreement Number W911NF-16-2-0120the “973 Program—the National Basic Research Program of China” Special Funds for the Chief Young Scientis(2015CB358600)the Excellent Young Scholar Fund from National Natural Science Foundation of China(21422103)the China Scholarship Council(CSC)
文摘Ternary transition metal dichalcogenide alloys with spatially graded bandgaps are an emerging class of two-dimensional materials with unique features,which opens up new potential for device applications.Here,visible–near-infrared and self-powered phototransistors based on spatially bandgap-graded MoS2(1−x)Se2x alloys,synthesized by a simple and controllable chemical solution deposition method,are reported.The graded bandgaps,arising from the spatial grading of Se composition and thickness within a single domain,are tuned from 1.83 to 1.73 eV,leading to the formation of a homojunction with a builtin electric field.Consequently,a strong and sensitive gate-modulated photovoltaic effect is demonstrated,enabling the homojunction phototransistors at zero bias to deliver a photoresponsivity of 311 mA W−1,a specific detectivity up to^10^11 Jones,and an on/off ratio up to^10^4.Remarkably,when illuminated by the lights ranging from 405 to 808 nm,the biased devices yield a champion photoresponsivity of 191.5 A W−1,a specific detectivity up to^1012 Jones,a photoconductive gain of 10^6–10^7,and a photoresponsive time in the order of^50 ms.These results provide a simple and competitive solution to the bandgap engineering of two-dimensional materials for device applications without the need for p–n junctions.
基金Project supported by the Construct Program of the Key Discipline in Hunan Province,ChinaAid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province,China
文摘First-principle calculations with different exchange-correlation functionals, including LDA, PBE, and vd W-DF functional in the form of opt B88-vd W, have been performed to investigate the electronic and elastic properties of twodimensional transition metal dichalcogenides（TMDCs） with the formula of MX2（M = Mo, W; X = O, S, Se, Te） in both monolayer and bilayer structures. The calculated band structures show a direct band gap for monolayer TMDCs at the K point except for MoO2 and WO2. When the monolayers are stacked into a bilayer, the reduced indirect band gaps are found except for bilayer WTe2, in which the direct gap is still present at the K point. The calculated in-plane Young moduli are comparable to that of graphene, which promises possible application of TMDCs in future flexible and stretchable electronic devices. We also evaluated the performance of different functionals including LDA, PBE, and opt B88-vd W in describing elastic moduli of TMDCs and found that LDA seems to be the most qualified method. Moreover, our calculations suggest that the Young moduli for bilayers are insensitive to stacking orders and the mechanical coupling between monolayers seems to be negligible.
基金supported by the National Natural Science Foundation of China(51322209 and 21473124)Sino-German Center for Research Promotion(GZ871)
文摘Newborn two-dimensional materials(NB2DMs) beyond graphene such as transition metal dichalcogenides(TMDs) exhibit excellent optoelectronic and mechanical properties as well as high theoretical specific capacity, which make them become the promising building blocks of flexible energy devices related to energy conversion and storage. Compared to graphene with zero band gap or traditional friable materials such as Si, these NB2 DMs are more suitable to construct flexible devices as active layers of optoelectronic devices or as active materials for batteries. The present review focuses on the recent advances in bendable energy devices based on NB2 DMs, including batteries, supercapacitors(SCs), solar cells, photodetectors and nanogenerators(NGs). The NB2 DMs pave a new way to construct next-generation flexible energy devices with improved performance and we believe that those devices will be seen in our daily life and change our lifestyle in the immediate future.
文摘过渡金属二硫化物(Transition Metal Dichalcogenides,TMDs)以其优异的光电子学特性,在诸如光捕获、光电探测、光电晶体管、发光二极管以及纳米激光器等领域中展现出了强大的应用潜力,成为当前研究前沿热点之一.少层TMDs材料的带隙处于可见和近红外区间,其激子在室温下具有很大的束缚能、高谐振子强度,且单层TMDs由于空间反演对称性的破缺具有能谷选择的圆二色性等,这些特性使得TMDs材料格外引人注目.金属纳米结构的表面等离激元具有亚波长的光局域特性,可通过合理的结构设计实现对其共振波长、频谱宽度、近场增强倍数、远场辐射特性的灵活控制.将等离激元光学结构和过渡金属二硫化物相结合可大幅拓宽纳米光子学前沿基础问题研究与纳米光电器件的设计应用.本文综述了表面等离激元和TMDs材料复合体系的最新研究进展,着重阐述了为何这类复合体系能够提供他们各自体系所不能具有的特性.比如,表面等离激元的近场增强(场局域)效应可极大增强许多纳米光学系统中的光与物质相互作用强度,可用于对TMDs材料的光吸收、光发射、光电流以及非线性光学等过程进行调制.TMDs材料具备的受外界环境调控的强激子效应和能谷选择的圆二色性等特性,可为表面等离激元纳米结构提供丰富的主动调制手段与能谷自由度.最后展望了该新型复合体系未来的研究方向和机遇.
基金Project supported by the National Basic Research Program of China(Grant No.2014CB643903)the National Natural Science Foundation of China(Grant Nos.61225021,11474272,11174272,and 11404324)K.C.Wong Education Foundation
文摘Transition metal dichalcogenides （TMDCs） have gained considerable attention because of their novel properties and great potential applications. The flakes of TMDCs not only have great light absorption from visible to near infrared, but also can be stacked together regardless of lattice mismatch like other two-dimensional （2D） materials. Along with the studies on intrinsic properties of TMDCs, the junctions based on TMDCs become more and more important in applications of photodetection. The junctions have shown many exciting possibilities to fully combine the advantages of TMDCs, other 2D materials, conventional and organic semiconductors together. Early studies have greatly enriched the application of TMDCs in photodetection. In this review, we investigate the efforts in photodetectors based on the junctions of TMDCs and analyze the properties of those photodetectors. Homojunctions based on TMDCs can be made by surface chemical doping, elemental doping and electrostatic gating. Heterojunction formed between TMDCs/2D materials, TMDCs/conventional semiconductors and TMDCs/organic semiconductor also deserve more attentions. We also compare the advantages and disadvantages of different junctions, and then give the prospects for the development of junctions based on TMDCs.
基金The authors acknowledge support by the Office of Naval Research under Grant No. N00014-16-1-3055, the U.S. Department of Energy, Office of Basic Energy Sciences, Divi- sion of Materials Sciences and Engineering under award No. DE- SC0012130, and National Science Foundation MRSEC program under grant No. DMR-1720139 at the Materials Research Center of Northwestern University.
文摘The explosion of interest in two-dimensional van der Waals materials has been in many ways driven by their layered geometry. This feature makes possible numerous avenues for assembling and ma- nipulating the optical and electronic properties of these materials. In the specific case of monolayer transition metal dichalcogenide semiconductors, the direct band gap combined with the flexibility for manipulation of layers has made this class of materials promising for optoelectronics. Here, we review the properties of these layered materials and the various means of engineering these properties for optoeleetronics. We summarize approaches for control that modify their structural and chemical en- vironment, and we give particular detail on the integration of these materials into engineered optical fields to control their optical characteristics. This combination of controllability from their layered surface structure and photonic environment provide an expansive landscape for novel optoelectronic phenomena.
