Two-dimensional transition metal dichalcogenides heterostructures have stimulated wide in- terest not only for the fundamental research, but also for the application of next generation electronic and optoelectronic de...Two-dimensional transition metal dichalcogenides heterostructures have stimulated wide in- terest not only for the fundamental research, but also for the application of next generation electronic and optoelectronic devices. Herein, we report a successful two-step chemical vapor deposition strategy to construct vertically stacked van der Waals epitaxial In2Se3/MoSe2 heterostructures. Transmission electron microscopy characterization reveals clearly that the In2Se3 has well-aligned lattice orientation with the substrate of monolayer MoSe2. Due to the interaction between the In2Se3 and MoSe2 layers, the heterostructure shows the quench- ing and red-shift of photoluminescence. Moreover, the current rectification behavior and photovoltaic effect can be observed from the heterostructure, which is attributed to the unique band structure alignment of the heterostructure, and is further confirmed by Kevin probe force microscopy measurement. The synthesis approach via van der Waals epitaxy in this work can expand the way to fabricate a variety of two-dimensional heterostructures for potential applications in electronic and optoelectronic devices.展开更多
Lithium-sulfur batteries(LSBs) hold great potential for large-scale electrochemical energy storage applications. Currently, the shuttle of soluble lithium polysulfide(LiPSs) intermediates with sluggish conversion kine...Lithium-sulfur batteries(LSBs) hold great potential for large-scale electrochemical energy storage applications. Currently, the shuttle of soluble lithium polysulfide(LiPSs) intermediates with sluggish conversion kinetics and random deposition of Li2S have severely degraded the capacity, rate and cycling performances of LSBs, preventing their practical applications. In this work, ultrathin MoSe2 nanosheets with active edge sites were successfully grown on both internal and external surfaces of hollow carbon spheres with mesoporous walls(MCHS). The resulting MoSe2@MCHS composite acted as a novel functional reservoir for Li PSs with high chemical affinity and effectively mediated their fast redox conversion during charge/discharge as elucidated by experimental observations and first-principles density functional theory(DFT) calculations. The as-fabricated Li-S cells delivered high capacity, superior rate and excellent cyclability. The current work presents new insights on the delicate design and fabrication of novel functional composite electrode materials for rechargeable batteries with emerging applications.展开更多
Photocatalysis activated by visible light remains highly challenging.Here,we report novel MoSe2/ZnO/ZnSe(ZM)hybrids fabricated via a simple hydrothermal method for photocatalytic reduction of Cr(VI)under visible light...Photocatalysis activated by visible light remains highly challenging.Here,we report novel MoSe2/ZnO/ZnSe(ZM)hybrids fabricated via a simple hydrothermal method for photocatalytic reduction of Cr(VI)under visible light irradiation.ZM hybrids show improved photocatalytic reduction ability under visible light irradiation compared to pure ZnO owing to good visible light absorption and rapid electron transfer and separation.The ZM hybrid shows the highest Cr(VI)reduction rate of 100%.Moreover,the photocatalytic Cr(VI)reduction process is mainly controlled by photoinduced electrons.展开更多
Interface engineering has been widely explored to improve the electrochemical performances of composite electrodes,which governs the interface charge transfer,electron transportation,and structural stability.Herein,Mo...Interface engineering has been widely explored to improve the electrochemical performances of composite electrodes,which governs the interface charge transfer,electron transportation,and structural stability.Herein,MoC is incorporated into MoSe2/C composite as an intermediate phase to alter the bridging between MoSe2-and nitrogen-doped three-dimensional(3D)carbon framework as MoSe2/MoC/N–C connection,which greatly improve the structural stability,electronic conductivity,and interfacial charge transfer.Moreover,the incorporation of MoC into the composites inhibits the overgrowth of MoSe2 nanosheets on the 3D carbon framework,producing much smaller MoSe2 nanodots.The obtained MoSe2 nanodots with fewer layers,rich edge sites,and heteroatom doping ensure the good kinetics to promote pseudo-capacitance contributions.Employing as anode material for lithium-ion batteries,it shows ultralong cycle life(with 90%capacity retention after 5000 cycles at 2 A g−1)and excellent rate capability.Moreover,the constructed LiFePO4//MoSe2/MoC/N–C full cell exhibits over 86%capacity retention at 2 A g−1 after 300 cycles.The results demonstrate the effectiveness of the interface engineering by incorporation of MoC as interface bridging intermediate to boost the lithium storage capability,which can be extended as a potential general strategy for the interface engineering of composite materials.展开更多
The optical, thermal and electrical properties of ultra-thin two-dimensional （2D） crystal materials are highly related to their thickness. Therefore, identifying the atomic planes of few-layer crystal materials rapi...The optical, thermal and electrical properties of ultra-thin two-dimensional （2D） crystal materials are highly related to their thickness. Therefore, identifying the atomic planes of few-layer crystal materials rapidly is crucial to fundamental study. Here, a simple technique was demonstrated based on optical contrast for counting atomic planes （n） of few-layer MoSe2 on SiO2/Si substrates. It is found that the optical contrast of single-layer MoSe2 depends on light wavelength and thickness of SiO2 on Si substrate. The data calculated based on a Fresnel law-based model as well as atomic force microscopy （AFM） mea- surements fit well with the values measured by spectro- scopic ellipsometer. Furthermore, the calculated and measured contrasts were integral and plotted, which can be used to determine the MoSe2 atomic planes （1 ≤ n ≤ 4） accurately and rapidly.展开更多
Dynamic processes of electron transfer by optical doping in monolayer MoSe2 at 6 K are investigated via measuring time resolved photoluminescence(PL)traces under different excitation powers.Time-dependent electron tra...Dynamic processes of electron transfer by optical doping in monolayer MoSe2 at 6 K are investigated via measuring time resolved photoluminescence(PL)traces under different excitation powers.Time-dependent electron transfer process can be analyzed by a power-law distribution of t^−α withα=0.1-0.24,depending on the laser excitation power.The average electron transfer time of approximately 27.65 s is obtained in the excitation power range of 0.5 to 100μW.As the temperature increases from 20 to 44 K,the energy difference between the neutral and charged excitons is observed to decrease.展开更多
Sb2S3 solar cells with substrate structure usually suffer from pretty low short circuit current(JSC)due to the defects and poor carrier transport.The Sb2S3,as a one-dimensional material,exhibits orientation-dependent ...Sb2S3 solar cells with substrate structure usually suffer from pretty low short circuit current(JSC)due to the defects and poor carrier transport.The Sb2S3,as a one-dimensional material,exhibits orientation-dependent carrier transport property.In this work,a thin MoSe2 layer is directly synthesized on the Mo substrate followed by depositing the Sb2S3 thin film.The x-ray diffraction(XRD)patterns confirm that a thin MoSe2 layer can improve the crystallization of the Sb2S3 film and induce(hk1)orientations,which can provide more carrier transport channels.Kelvin probe force microscopy(KPFM)results suggest that this modified Sb2S3 film has a benign surface with less defects and dangling bonds.The variation of the surface potential of Sb2S3 indicates a much more efficient carrier separation.Consequently,the power conversion efficiency(PCE)of the substrate structured Sb2S3 thin film solar cell is improved from 1.36%to 1.86%,which is the best efficiency of the substrate structured Sb2S3 thin film solar cell,and JSC significantly increases to 13.6 mA/cm^2.According to the external quantum efficiency(EQE)and C-V measurements,the modified crystallization and elevated built-in electric field are the main causes.展开更多
Optoelectronic properties of MoSe2 are modulated by controlled annealing in air.Characterizations by Raman spectroscopy and XPS demonstrate the introduction of oxygen defects.Considerable increase in electron and hole...Optoelectronic properties of MoSe2 are modulated by controlled annealing in air.Characterizations by Raman spectroscopy and XPS demonstrate the introduction of oxygen defects.Considerable increase in electron and hole mobilities reveals the highly improved electron and hole transport.Furthermore,the photocurrent is enhanced by nearly four orders of magnitudes under 7 nW laser exposure after annealing.The remarkable enhancement in the photoresponse is attributed to an increase in hole trapping centers and a reduction in resistance.Furthermore,the annealed photodetector shows a fast time response on the order of 10 ms and responsivity of 3×10^(4) A/W.展开更多
Using the first-principles calculations, we study the structural, electronic, and magnetic properties of vanadium adsorbed MoSe_2 monolayer, and the magnetic couplings between the V adatoms at different adsorption con...Using the first-principles calculations, we study the structural, electronic, and magnetic properties of vanadium adsorbed MoSe_2 monolayer, and the magnetic couplings between the V adatoms at different adsorption concentrations. The calculations show that the V atom is chemically adsorbed on the MoSe_2 monolayer and prefers the location on the top of an Mo atom surrounded by three nearest-neighbor Se atoms. The interatomic electron transfer from the V to the nearestneighbor Se results in the polarized covalent bond with weak covalency, associated with the hybridizations of V with Se and Mo. The V adatom induces local impurity states in the middle of the band gap of pristine MoSe_2, and the peak of density of states right below the Fermi energy is associated with the V- dz^2 orbital. A single V adatom induces a magnetic moment of 5 μBthat mainly distributes on the V-3d and Mo-4d orbitals. The V adatom is in high-spin state, and its local magnetic moment is associated with the mid-gap impurity states that are mainly from the V-3d orbitals. In addition,the crystal field squashes a part of the V-4s electrons into the V-3d orbitals, which enhances the local magnetic moment.The magnetic ground states at different adsorption concentrations are calculated by generalized gradient approximations（GGA） and GGA＋U with enhanced electron localization. In addition, the exchange integrals between the nearest-neighbor V adatoms at different adsorption concentrations are calculated by fitting the first-principle total energies of ferromagnetic（FM） and antiferromagnetic（AFM） states to the Heisenberg model. The calculations with GGA show that there is a transition from ferromagnetic to antiferromagnetic ground state with increasing the distance between the V adatoms. We propose an exchange mechanism based on the on-site exchange on Mo and the hybridization between Mo and V, to explain the strong ferromagnetic coupling at a short distance between the V adatoms. However, the ferromagnetic exchange mechanism is sensitive to both the increased inter-adatom distance at low concentration and the enhanced electron localization by GGA＋U, which leads to antiferromagnetic ground state, where the antiferromagnetic superexchange is dominant.展开更多
多硫化物的穿梭效应是锂硫(Li-S)电池最致命的固有问题。本文通过在商业聚丙烯隔膜上涂覆碳纳米管支撑的MoSe2纳米片,成功构建了对多硫化物具有强吸附作用的功能化夹层,有效抑制了多硫化物穿梭效应的发生。将该功能化隔膜用于锂硫电池,...多硫化物的穿梭效应是锂硫(Li-S)电池最致命的固有问题。本文通过在商业聚丙烯隔膜上涂覆碳纳米管支撑的MoSe2纳米片,成功构建了对多硫化物具有强吸附作用的功能化夹层,有效抑制了多硫化物穿梭效应的发生。将该功能化隔膜用于锂硫电池,可获得良好的储能性质。在电流密度为0.1C时,电池的初始比容量高达1485 mAh g^−1。在高电流密度(2C)下,电池的比容量仍能达到880 mAh g^−1,说明电池的倍率性能较好。此外,电池在电流密度为0.5 C时表现出优异的长期循环稳定性。在循环300次的过程中,电池每圈容量的衰减率仅为0.093%。这些优异的储能特性得益于MoSe2对多硫化物的强吸附作用以及CNTs良好的导电性。展开更多
Molybdenum selenide is a potential alternative to counter electrode of a platinum-free dye-sensitized solar cell(DSSC). In this work, an in situ magnetron sputtering method is developed to prepare MoSe2 electrodes. Th...Molybdenum selenide is a potential alternative to counter electrode of a platinum-free dye-sensitized solar cell(DSSC). In this work, an in situ magnetron sputtering method is developed to prepare MoSe2 electrodes. The MoSe2 electrodes obtained at various temperatures from 300 and 550 ℃ are used as counter electrode for a dye-sensitized solar cell. Photovoltaic measurement results indicate that the MoSe2 electrodes prepared at 400 ℃ has the optimized performance, and the corresponding DSSCs provide an energy conversion efficiency of 6.83% which is comparable than that of the reference DSSC with platinum as counter electrode(6.51%). With further increasing the preparation temperature of the MoSe2 electrodes, the corresponding DSSCs decrease gradually to 5.96% for 550 ℃. Electrochemical impedance spectra(EIS) reveal that charge transfer resistance(Rct) of MoSe2 electrodes is rising with increase of the temperature from 400 to 500 ℃, suggesting a downward electrocatalytic activity. Though the MoSe2 electrode prepared at 550 ℃ show a reduced Rct, its series resistance(Rs) and diffusion resistance(Zw) increase obviously. Considering that MoSe2 phase cannot be formed at 300 ℃, it can be concluded that the prepared temperature as low as possible is favored for its final electrochemical performance. The results are very significant for developing low-cost and responsible counter electrodes for dye-sensitized solar cells.展开更多
A facile colloidal route to synthesize MoSe2 porous microspheres with diameters of 400-600 nm made up of MoSe2 monolayer flakes （-0.7 nm in thickness） is reported. The solvents trioctylamine （TOA） and oleylamine ...A facile colloidal route to synthesize MoSe2 porous microspheres with diameters of 400-600 nm made up of MoSe2 monolayer flakes （-0.7 nm in thickness） is reported. The solvents trioctylamine （TOA） and oleylamine （OAM） are found to play important roles in the formation of MoSe2 microspheres, whereby TOA determines the three-dimensional （3D） microspherical morphology and OAM directs the formation of MoSes monolayer flakes. The robust 3D MoSe2 microspheres exhibit remarkable activity and durability for the electrocatalytic hydrogen evolution reaction （HER） in acid, maintaining a small onset overpotential of -77 mV and keeping a small overpotential of 100 mV for a current density of 5 mA/cm2 after 1,000 cycles. In addition, similar 3D WSe2 microspheres can also be prepared by using this method. We expect this facile colloidal route could further be expanded to synthesize other porous structures which will find applications in fields such as in energy storage, catalysis, and sensing.展开更多
Layered semiconductors with atomic thicknesses are becoming increasingly important as active elements in high-performance electronic devices owing to their high carrier mobilities, large surface-to-volume ratios, and ...Layered semiconductors with atomic thicknesses are becoming increasingly important as active elements in high-performance electronic devices owing to their high carrier mobilities, large surface-to-volume ratios, and rapid electrical responses to their surrounding environments. Here, we report the first implementation of a highly sensitive chemical-vapor-deposition-grown multilayer MoSe2 field-effect transistor （FET） in a NO2 gas sensor. This sensor exhibited ultra-high sensitivity （S = ca. 1,907 for NO2 at 300 ppm）, real-time response, and rapid on-off switching. The high sensitivity of our MoSe2 gas sensor is attributed to changes in the gap states near the valence band induced by the NO2 gas absorbed in the MoSe2, which leads to a significant increase in hole current in the off-state regime. Device modeling and quantum transport simulations revealed that the variation of gap states with NO2 concentration is the key mechanism in a MoSe2 FET-based NO2 gas sensor. This comprehensive study, which addresses material growth, device fabrication, characterization, and device simulations, not only indicates the utility of MoSe2 FETs for high-performance chemical sensors, but also establishes a fundamental understanding of how surface chemistry influences carrier transport in layered semiconductor devices.展开更多
文摘Two-dimensional transition metal dichalcogenides heterostructures have stimulated wide in- terest not only for the fundamental research, but also for the application of next generation electronic and optoelectronic devices. Herein, we report a successful two-step chemical vapor deposition strategy to construct vertically stacked van der Waals epitaxial In2Se3/MoSe2 heterostructures. Transmission electron microscopy characterization reveals clearly that the In2Se3 has well-aligned lattice orientation with the substrate of monolayer MoSe2. Due to the interaction between the In2Se3 and MoSe2 layers, the heterostructure shows the quench- ing and red-shift of photoluminescence. Moreover, the current rectification behavior and photovoltaic effect can be observed from the heterostructure, which is attributed to the unique band structure alignment of the heterostructure, and is further confirmed by Kevin probe force microscopy measurement. The synthesis approach via van der Waals epitaxy in this work can expand the way to fabricate a variety of two-dimensional heterostructures for potential applications in electronic and optoelectronic devices.
基金financially supported by the National Natural Science Foundation of China (51302204, 21902122)Postdoctoral Science Foundation of China (2019M652723)+2 种基金Hunan Provincial Science and Technology Plan Project (No.2017TP1001)Program for Changjiang Scholars and Innovative Research Team in University (IRT_15R52)Hubei Provincial Department of Education for the “Chutian Scholar” program。
文摘Lithium-sulfur batteries(LSBs) hold great potential for large-scale electrochemical energy storage applications. Currently, the shuttle of soluble lithium polysulfide(LiPSs) intermediates with sluggish conversion kinetics and random deposition of Li2S have severely degraded the capacity, rate and cycling performances of LSBs, preventing their practical applications. In this work, ultrathin MoSe2 nanosheets with active edge sites were successfully grown on both internal and external surfaces of hollow carbon spheres with mesoporous walls(MCHS). The resulting MoSe2@MCHS composite acted as a novel functional reservoir for Li PSs with high chemical affinity and effectively mediated their fast redox conversion during charge/discharge as elucidated by experimental observations and first-principles density functional theory(DFT) calculations. The as-fabricated Li-S cells delivered high capacity, superior rate and excellent cyclability. The current work presents new insights on the delicate design and fabrication of novel functional composite electrode materials for rechargeable batteries with emerging applications.
基金Financial support from the Natural Science Foundation of Zhejiang Province(LY18E060005,LY19E020006)~~
文摘Photocatalysis activated by visible light remains highly challenging.Here,we report novel MoSe2/ZnO/ZnSe(ZM)hybrids fabricated via a simple hydrothermal method for photocatalytic reduction of Cr(VI)under visible light irradiation.ZM hybrids show improved photocatalytic reduction ability under visible light irradiation compared to pure ZnO owing to good visible light absorption and rapid electron transfer and separation.The ZM hybrid shows the highest Cr(VI)reduction rate of 100%.Moreover,the photocatalytic Cr(VI)reduction process is mainly controlled by photoinduced electrons.
基金This work was supported by the National Natural Science Foundation of China(No 51872334,51932011,51874326,51572299)the Natural Science Foundation of Hunan Province for Distinguished Young Scholars(2018JJ1036)the Independent exploration and innovation Project for graduate students of central south university(2019zzts049).
文摘Interface engineering has been widely explored to improve the electrochemical performances of composite electrodes,which governs the interface charge transfer,electron transportation,and structural stability.Herein,MoC is incorporated into MoSe2/C composite as an intermediate phase to alter the bridging between MoSe2-and nitrogen-doped three-dimensional(3D)carbon framework as MoSe2/MoC/N–C connection,which greatly improve the structural stability,electronic conductivity,and interfacial charge transfer.Moreover,the incorporation of MoC into the composites inhibits the overgrowth of MoSe2 nanosheets on the 3D carbon framework,producing much smaller MoSe2 nanodots.The obtained MoSe2 nanodots with fewer layers,rich edge sites,and heteroatom doping ensure the good kinetics to promote pseudo-capacitance contributions.Employing as anode material for lithium-ion batteries,it shows ultralong cycle life(with 90%capacity retention after 5000 cycles at 2 A g−1)and excellent rate capability.Moreover,the constructed LiFePO4//MoSe2/MoC/N–C full cell exhibits over 86%capacity retention at 2 A g−1 after 300 cycles.The results demonstrate the effectiveness of the interface engineering by incorporation of MoC as interface bridging intermediate to boost the lithium storage capability,which can be extended as a potential general strategy for the interface engineering of composite materials.
基金financially supported by the Research Funds of Renmin University of China(Nos.13XNLF02 and 14XNLQ07)the National Natural Science Foundation of China(Nos.11304381,11004245,11174366 and 51202200)
文摘The optical, thermal and electrical properties of ultra-thin two-dimensional （2D） crystal materials are highly related to their thickness. Therefore, identifying the atomic planes of few-layer crystal materials rapidly is crucial to fundamental study. Here, a simple technique was demonstrated based on optical contrast for counting atomic planes （n） of few-layer MoSe2 on SiO2/Si substrates. It is found that the optical contrast of single-layer MoSe2 depends on light wavelength and thickness of SiO2 on Si substrate. The data calculated based on a Fresnel law-based model as well as atomic force microscopy （AFM） mea- surements fit well with the values measured by spectro- scopic ellipsometer. Furthermore, the calculated and measured contrasts were integral and plotted, which can be used to determine the MoSe2 atomic planes （1 ≤ n ≤ 4） accurately and rapidly.
基金supported by the National Natural Science Foundation of China under Grant Nos 61674135,11974342 and 61827823.
文摘Dynamic processes of electron transfer by optical doping in monolayer MoSe2 at 6 K are investigated via measuring time resolved photoluminescence(PL)traces under different excitation powers.Time-dependent electron transfer process can be analyzed by a power-law distribution of t^−α withα=0.1-0.24,depending on the laser excitation power.The average electron transfer time of approximately 27.65 s is obtained in the excitation power range of 0.5 to 100μW.As the temperature increases from 20 to 44 K,the energy difference between the neutral and charged excitons is observed to decrease.
基金Project supported by the National Key R&D Program of China(Grant Nos.2019YFB1503500,2018YFE0203400,and 2018YFB1500200)the National Natural Science Foundation of China(Grant No.U1902218)+1 种基金the YangFan Innovative and Entrepreneurial Research Team Project of China(Grant No.2014YT02N037)the 111 Project,China(Grant No.B16027).
文摘Sb2S3 solar cells with substrate structure usually suffer from pretty low short circuit current(JSC)due to the defects and poor carrier transport.The Sb2S3,as a one-dimensional material,exhibits orientation-dependent carrier transport property.In this work,a thin MoSe2 layer is directly synthesized on the Mo substrate followed by depositing the Sb2S3 thin film.The x-ray diffraction(XRD)patterns confirm that a thin MoSe2 layer can improve the crystallization of the Sb2S3 film and induce(hk1)orientations,which can provide more carrier transport channels.Kelvin probe force microscopy(KPFM)results suggest that this modified Sb2S3 film has a benign surface with less defects and dangling bonds.The variation of the surface potential of Sb2S3 indicates a much more efficient carrier separation.Consequently,the power conversion efficiency(PCE)of the substrate structured Sb2S3 thin film solar cell is improved from 1.36%to 1.86%,which is the best efficiency of the substrate structured Sb2S3 thin film solar cell,and JSC significantly increases to 13.6 mA/cm^2.According to the external quantum efficiency(EQE)and C-V measurements,the modified crystallization and elevated built-in electric field are the main causes.
基金Project supported by the National Natural Science Foundation of China(Grant No.61904043)the Natural Science Foundation of Zhejiang Province,China(Grant No.LQ19A040009).
文摘Optoelectronic properties of MoSe2 are modulated by controlled annealing in air.Characterizations by Raman spectroscopy and XPS demonstrate the introduction of oxygen defects.Considerable increase in electron and hole mobilities reveals the highly improved electron and hole transport.Furthermore,the photocurrent is enhanced by nearly four orders of magnitudes under 7 nW laser exposure after annealing.The remarkable enhancement in the photoresponse is attributed to an increase in hole trapping centers and a reduction in resistance.Furthermore,the annealed photodetector shows a fast time response on the order of 10 ms and responsivity of 3×10^(4) A/W.
基金Project supported by the National Basic Research Program of China(Grant No.2011CB606405)the CAEP Microsystem and THz Science and Technology Foundation,China(Grant No.CAEPMT201501)the Science Challenge Project,China(Grant No.JCKY2016212A503)
文摘Using the first-principles calculations, we study the structural, electronic, and magnetic properties of vanadium adsorbed MoSe_2 monolayer, and the magnetic couplings between the V adatoms at different adsorption concentrations. The calculations show that the V atom is chemically adsorbed on the MoSe_2 monolayer and prefers the location on the top of an Mo atom surrounded by three nearest-neighbor Se atoms. The interatomic electron transfer from the V to the nearestneighbor Se results in the polarized covalent bond with weak covalency, associated with the hybridizations of V with Se and Mo. The V adatom induces local impurity states in the middle of the band gap of pristine MoSe_2, and the peak of density of states right below the Fermi energy is associated with the V- dz^2 orbital. A single V adatom induces a magnetic moment of 5 μBthat mainly distributes on the V-3d and Mo-4d orbitals. The V adatom is in high-spin state, and its local magnetic moment is associated with the mid-gap impurity states that are mainly from the V-3d orbitals. In addition,the crystal field squashes a part of the V-4s electrons into the V-3d orbitals, which enhances the local magnetic moment.The magnetic ground states at different adsorption concentrations are calculated by generalized gradient approximations（GGA） and GGA＋U with enhanced electron localization. In addition, the exchange integrals between the nearest-neighbor V adatoms at different adsorption concentrations are calculated by fitting the first-principle total energies of ferromagnetic（FM） and antiferromagnetic（AFM） states to the Heisenberg model. The calculations with GGA show that there is a transition from ferromagnetic to antiferromagnetic ground state with increasing the distance between the V adatoms. We propose an exchange mechanism based on the on-site exchange on Mo and the hybridization between Mo and V, to explain the strong ferromagnetic coupling at a short distance between the V adatoms. However, the ferromagnetic exchange mechanism is sensitive to both the increased inter-adatom distance at low concentration and the enhanced electron localization by GGA＋U, which leads to antiferromagnetic ground state, where the antiferromagnetic superexchange is dominant.
文摘多硫化物的穿梭效应是锂硫(Li-S)电池最致命的固有问题。本文通过在商业聚丙烯隔膜上涂覆碳纳米管支撑的MoSe2纳米片,成功构建了对多硫化物具有强吸附作用的功能化夹层,有效抑制了多硫化物穿梭效应的发生。将该功能化隔膜用于锂硫电池,可获得良好的储能性质。在电流密度为0.1C时,电池的初始比容量高达1485 mAh g^−1。在高电流密度(2C)下,电池的比容量仍能达到880 mAh g^−1,说明电池的倍率性能较好。此外,电池在电流密度为0.5 C时表现出优异的长期循环稳定性。在循环300次的过程中,电池每圈容量的衰减率仅为0.093%。这些优异的储能特性得益于MoSe2对多硫化物的强吸附作用以及CNTs良好的导电性。
基金supported by the National Basic Research Program(973 Program,2015CB251100)Natural Science Foundation of Tianjin(18JCZDJC31000)~~
文摘Molybdenum selenide is a potential alternative to counter electrode of a platinum-free dye-sensitized solar cell(DSSC). In this work, an in situ magnetron sputtering method is developed to prepare MoSe2 electrodes. The MoSe2 electrodes obtained at various temperatures from 300 and 550 ℃ are used as counter electrode for a dye-sensitized solar cell. Photovoltaic measurement results indicate that the MoSe2 electrodes prepared at 400 ℃ has the optimized performance, and the corresponding DSSCs provide an energy conversion efficiency of 6.83% which is comparable than that of the reference DSSC with platinum as counter electrode(6.51%). With further increasing the preparation temperature of the MoSe2 electrodes, the corresponding DSSCs decrease gradually to 5.96% for 550 ℃. Electrochemical impedance spectra(EIS) reveal that charge transfer resistance(Rct) of MoSe2 electrodes is rising with increase of the temperature from 400 to 500 ℃, suggesting a downward electrocatalytic activity. Though the MoSe2 electrode prepared at 550 ℃ show a reduced Rct, its series resistance(Rs) and diffusion resistance(Zw) increase obviously. Considering that MoSe2 phase cannot be formed at 300 ℃, it can be concluded that the prepared temperature as low as possible is favored for its final electrochemical performance. The results are very significant for developing low-cost and responsible counter electrodes for dye-sensitized solar cells.
文摘A facile colloidal route to synthesize MoSe2 porous microspheres with diameters of 400-600 nm made up of MoSe2 monolayer flakes （-0.7 nm in thickness） is reported. The solvents trioctylamine （TOA） and oleylamine （OAM） are found to play important roles in the formation of MoSe2 microspheres, whereby TOA determines the three-dimensional （3D） microspherical morphology and OAM directs the formation of MoSes monolayer flakes. The robust 3D MoSe2 microspheres exhibit remarkable activity and durability for the electrocatalytic hydrogen evolution reaction （HER） in acid, maintaining a small onset overpotential of -77 mV and keeping a small overpotential of 100 mV for a current density of 5 mA/cm2 after 1,000 cycles. In addition, similar 3D WSe2 microspheres can also be prepared by using this method. We expect this facile colloidal route could further be expanded to synthesize other porous structures which will find applications in fields such as in energy storage, catalysis, and sensing.
文摘Layered semiconductors with atomic thicknesses are becoming increasingly important as active elements in high-performance electronic devices owing to their high carrier mobilities, large surface-to-volume ratios, and rapid electrical responses to their surrounding environments. Here, we report the first implementation of a highly sensitive chemical-vapor-deposition-grown multilayer MoSe2 field-effect transistor （FET） in a NO2 gas sensor. This sensor exhibited ultra-high sensitivity （S = ca. 1,907 for NO2 at 300 ppm）, real-time response, and rapid on-off switching. The high sensitivity of our MoSe2 gas sensor is attributed to changes in the gap states near the valence band induced by the NO2 gas absorbed in the MoSe2, which leads to a significant increase in hole current in the off-state regime. Device modeling and quantum transport simulations revealed that the variation of gap states with NO2 concentration is the key mechanism in a MoSe2 FET-based NO2 gas sensor. This comprehensive study, which addresses material growth, device fabrication, characterization, and device simulations, not only indicates the utility of MoSe2 FETs for high-performance chemical sensors, but also establishes a fundamental understanding of how surface chemistry influences carrier transport in layered semiconductor devices.
