FacebookTwitterRssLinkedInEmail

Electronic structure and charge-density wave transition in monolayer VS_{2}. (arXiv:2104.02217v1 [cond-mat.str-el])

2021-04-07T02:29:27+00:00April 7th, 2021|Categories: Publications|Tags: , |

Vanadium disulfide (VS_{2}) attracts elevated interests for its charge-density wave (CDW) phase transition, ferromagnetism, and catalytic reactivity, but the electronic structure of monolayer has not been well understood yet. Here we report synthesis of epitaxial 1T VS_{2} monolayer on bilayer graphene grown by molecular-beam epitaxy (MBE). Angle-resolved photoemission spectroscopy (ARPES) measurements reveal that Fermi surface with six elliptical pockets centered at the M points shows gap opening at low temperature. Temperature-dependence of the gap size suggests existence of CDW phase transition above room temperature. Our observations provide important evidence to understand the strongly correlated electron physics and the related surface catalytic properties in two-dimensional transition-metal dichalcogenides (TMDCs).

Published in: "arXiv Material Science".

Doping Concentration Modulation in Vanadium Doped Monolayer Molybdenum Disulfide for Synaptic Transistors. (arXiv:2103.12262v1 [cond-mat.mtrl-sci])

2021-03-24T02:29:25+00:00March 24th, 2021|Categories: Publications|Tags: , |

Doping is an effective way to modify the electronic property of two-dimensional (2D) materials and endow them with new functionalities. However, wide-range control of the substitutional doping concentration with large scale uniformity remains challenging in 2D materials. Here we report in-situ chemical vapor deposition growth of vanadium (V) doped monolayer molybdenum disulfide (MoS2) with widely tunable doping concentrations ranging from 0.3 to 13.1 at%. The key to regulate the doping concentration lies in the use of appropriate V precursors with different doping abilities, which also generate a large-scale uniform doping effect. Artificial synaptic transistors were fabricated by using the heavily doped MoS2 as the channel material for the first time. Synaptic potentiation, depression and repetitive learning processes are mimicked by the gate-tunable channel conductance change in such transistors with abundant V atoms to trap/detrap electrons. This work shows a feasible method to dope monolayer 2D semiconductors and demonstrates their use in artificial synaptic transistors.

Published in: "arXiv Material Science".

A full gap above the Fermi level: the charge density wave of monolayer VS2. (arXiv:2101.01140v1 [cond-mat.mtrl-sci])

2021-01-05T02:29:20+00:00January 5th, 2021|Categories: Publications|Tags: |

In the weak-coupling Peierls’ view, charge density wave (CDW) transitions are metal-insulator transitions, creating a gap at the Fermi level. However, with strong electron-phonon coupling, theoretically the effects of the periodic lattice distortion could be spread throughout the electronic structure and give rise to CDW gaps away from the Fermi level. Here, using scanning tunneling microscopy and spectroscopy, we present experimental evidence of a full CDW gap residing in the unoccupied states of monolayer VS2. Our ab initio calculations show anharmonic coupling of transverse and longitudinal phonons to be essential for the formation of the CDW and the full gap above the Fermi level. The CDW induces a Lifshitz transition, i.e., a topological metal-metal instead of a Peierls metal-insulator transition. Additionally, x-ray magnetic circular dichroism reveals the absence of net magnetization in this phase, pointing to a coupled CDW-antiferromagnetic ground state.

Published in: "arXiv Material Science".

Intercorrelated ferroelectrics in 2D van der Waals materials. (arXiv:2011.10914v1 [cond-mat.mtrl-sci])

2020-11-24T02:29:39+00:00November 24th, 2020|Categories: Publications|Tags: , , , , |

2D intercorrelated ferroelectrics, exhibiting a coupled in-plane and out-of-plane ferroelectricity, is a fundamental phenomenon in the field of condensed-mater physics. The current research is based on the paradigm of bi-directional inversion asymmetry in single-layers, which restricts 2D intercorrelated ferroelectrics to extremely few systems. Herein, we propose a new scheme for achieving 2D intercorrelated ferroelectrics using van der Waals (vdW) interaction, and apply this scheme to a vast family of 2D vdW materials. Using first-principles, we demonstrate that 2D vdW multilayers-for example, BN, MoS2, InSe, CdS, PtSe2, TI2O, SnS2, Ti2CO2 etc.- can exhibit coupled in-plane and out-of-plane ferroelectricity, thus yielding 2D intercorrelated ferroelectricsferroelectric physics. We further predict that such intercorrelated ferroelectrics could demonstrate many distinct properties, for example, electrical full control of spin textures in trilayer PtSe2 and electrical permanent control of valley-contrasting physics in four-layer VS2. Our finding opens a new direction for 2D intercorrelated ferroelectric research.

Published in: "arXiv Material Science".

Substitutional VSn nanodispersed in MoS$_2$ film for Pt-scalable catalyst. (arXiv:2010.10908v1 [cond-mat.mtrl-sci])

2020-10-22T02:29:33+00:00October 22nd, 2020|Categories: Publications|Tags: , , |

Among transition metal dichalcogenides (TMdCs) as alternatives for Pt-based catalysts, metallic-TMdCs catalysts have highly reactive basal-plane but are unstable. Meanwhile, chemically stable semiconducting-TMdCs show limiting catalytic activity due to their inactive basal-plane. Here, we propose metallic vanadium sulfide (VSn) nanodispersed in a semiconducting MoS2 film (V-MoS2) as an efficient catalyst. During synthesis, vanadium atoms are substituted into hexagonal monolayer MoS2 to form randomly distributed VSn units. The V-MoS2 film on a Cu electrode exhibits Pt-scalable catalytic performance; current density of 1000 mA cm-2 at 0.6 V, overpotential of -0.06 V at a current density of 10 mA cm-2 and exchange current density of 0.65 mA cm-2 at 0 V with excellent cycle stability for hydrogen-evolution-reaction (HER). The high intrinsic HER performance of V-MoS2 is explained by the efficient electron transfer from the Cu electrode to chalcogen vacancies near vanadium sites with optimal Gibbs free energy (-0.02 eV). This study adds insight into ways to engineer TMdCs at the atomic-level to boost intrinsic catalytic activity for hydrogen evolution.

Published in: "arXiv Material Science".

Multifunctional Lateral Transition-Metal Disulfides Heterojunctions. (arXiv:2005.00258v1 [cond-mat.mtrl-sci])

2020-05-04T02:29:25+00:00May 4th, 2020|Categories: Publications|Tags: , |

The intrinsic spin-dependent transport properties of two types of lateral VS2|MoS2 heterojunctions are systematically investigated using first-principles calculations, and their various nanodevices with novel properties are designed. The lateral VS2|MoS2 heterojunction diodes show a perfect rectifying effect and are promising for the applications of Schottky diodes. A large spin-polarization ratio is observed for the A-type device and pure spin-mediated current is then realized. The gate voltage significantly tunes the current and rectification ratio of their field-effect transistors (FETs). In addition, they all have sensitive photoresponse to blue light, and could be used as photodetector and photovoltaic device. Moreover, they generate the effective thermally-driven current when a temperature gratitude appears between the two terminals, suggesting them as potential thermoelectric materials. Hence, the lateral VS2|MoS2 heterojunctions show a multifunctional nature and have various potential applications in spintronics, optoelectronics, and spin caloritronics.

Published in: "arXiv Material Science".

Hierarchical Composite of Rose‐Like VS2@S/N‐Doped Carbon with Expanded (001) Planes for Superior Li‐Ion Storage

2019-12-03T06:36:39+00:00December 3rd, 2019|Categories: Publications|Tags: , |

A hierarchical composite of rose‐like VS2@S/N‐doped carbon with expanded (001) planes is synthesized via a facile one‐pot solvothermal route. Benefiting from outstanding conductivity, improved Li+ diffusion kinetics, and hierarchical structure, the VS2@SNC electrode exhibits an outstanding rate capability and a remarkable long‐term cycling stability with a capacity of 684.5 mA h g−1 after 600 cycles at 8 A g−1. Abstract In the present work, a hierarchical composite of rose‐like VS2@S/N‐doped carbon (VS2@SNC) with expanded (001) planes is successfully fabricated through a facile synthetic route. Notably, the d‐spacing of (001) planes is expanded to 0.92 nm, which is proved to dramatically reduce the energy barrier for Li+ diffusion in the composite of VS2@SNC by density functional theory calculation. On the other hand, the S/N‐doped carbon in the composite greatly promotes the electrical conductivity and enhances the structural stability. In addition, the hierarchical structure of VS2@SNC facilitates rapid electrolyte diffusion and increases the contact area between the electrode and electrolyte simultaneously. Benefiting from the merits mentioned above, the VS2@SNC electrode exhibits excellent electrochemical properties, such as a large reversible capacity of 971.6 mA h g−1 at 0.2 A g−1, an extremely high rate capability of 772.1 mA h g−1 at 10 A g−1, and a remarkable cycling stability up to 600 cycles at 8 A g−1 with a capacity of 684.5 mA h g−1, making it a promising candidate as an anode material for lithium‐ion batteries.

Published in: "Small".

Hierarchical Composite of Rose‐Like VS2@S/N‐Doped Carbon with Expanded (001) Planes for Superior Li‐Ion Storage

2019-11-21T06:34:21+00:00November 21st, 2019|Categories: Publications|Tags: , |

A hierarchical composite of rose‐like VS2@S/N‐doped carbon with expanded (001) planes is synthesized via a facile one‐pot solvothermal route. Benefiting from outstanding conductivity, improved Li+ diffusion kinetics, and hierarchical structure, the VS2@SNC electrode exhibits an outstanding rate capability and a remarkable long‐term cycling stability with a capacity of 684.5 mA h g−1 after 600 cycles at 8 A g−1. Abstract In the present work, a hierarchical composite of rose‐like VS2@S/N‐doped carbon (VS2@SNC) with expanded (001) planes is successfully fabricated through a facile synthetic route. Notably, the d‐spacing of (001) planes is expanded to 0.92 nm, which is proved to dramatically reduce the energy barrier for Li+ diffusion in the composite of VS2@SNC by density functional theory calculation. On the other hand, the S/N‐doped carbon in the composite greatly promotes the electrical conductivity and enhances the structural stability. In addition, the hierarchical structure of VS2@SNC facilitates rapid electrolyte diffusion and increases the contact area between the electrode and electrolyte simultaneously. Benefiting from the merits mentioned above, the VS2@SNC electrode exhibits excellent electrochemical properties, such as a large reversible capacity of 971.6 mA h g−1 at 0.2 A g−1, an extremely high rate capability of 772.1 mA h g−1 at 10 A g−1, and a remarkable cycling stability up to 600 cycles at 8 A g−1 with a capacity of 684.5 mA h g−1, making it a promising candidate as an anode material for lithium‐ion batteries.

Published in: "Small".

Vanadium trimers randomly aligned along the c-axis direction in layered LiVO2. (arXiv:1910.01337v1 [cond-mat.str-el])

2019-10-04T02:29:21+00:00October 4th, 2019|Categories: Publications|Tags: |

Herein, we discuss the identification of vanadium trimers in layered LiVO2 and its sulfide analog of LiVS2 with two-dimensional triangular lattices. Our comprehensive structural studies using synchrotron X-ray diffraction experiments clarified that vanadium trimers are randomly aligned along the c-axis direction in LiVO2, while the long-range ordering of vanadium trimers along the c-axis direction appears in LiVS2. Our results solve the longstanding issue of cluster patterns in LiVO2 and provide an experimental basis for identifying the mechanism of trimer formation.

Published in: "arXiv Material Science".

Rational Design of Nanoporous MoS2/VS2 Heteroarchitecture for Ultrahigh Performance Ammonia Sensors

2019-09-14T00:38:21+00:00September 14th, 2019|Categories: Publications|Tags: , , , |

2D MoS2/VS2 heterostructures with ultrahigh performance for ammonia sensing are demonstrated. The growth of MoS2 nanosheets on porous VS2 microflowers affords better structural stability for the heterostructure during continuous adsorption of ammonia. The excellent sensing performance is attributed to the high affinity of the MoS2/VS2 heterostructure toward ammonia and the enhanced electronic effects arising from the heterostructure formation. Abstract 2D transition metal dichalcogenides (TMDs) have received widespread interest by virtue of their excellent electrical, optical, and electrochemical characteristics. Recent studies on TMDs have revealed their versatile utilization as electrocatalysts, supercapacitors, battery materials, and sensors, etc. In this study, MoS2 nanosheets are successfully assembled on the porous VS2 (P‐VS2) scaffold to form a MoS2/VS2 heterostructure. Their gas‐sensing features, such as sensitivity and selectivity, are investigated by using a quartz crystal microbalance (QCM) technique. The QCM results and density functional theory (DFT) calculations reveal the impressive affinity of the MoS2/VS2 heterostructure sensor toward ammonia with a higher adsorption uptake than the pristine MoS2 or P‐VS2 sensor. Furthermore, the adsorption kinetics of the MoS2/VS2 heterostructure sensor toward ammonia follow the pseudo‐first‐order kinetics model. The excellent sensing features of the MoS2/VS2 heterostructure render it attractive for high‐performance ammonia sensors in diverse applications.

Published in: "Small".

A Highly Reversible Zn Anode with Intrinsically Safe Organic Electrolyte for Long‐Cycle‐Life Batteries

2019-07-23T08:44:06+00:00July 23rd, 2019|Categories: Publications|Tags: , , |

Trimethyl phosphate (TMP) is adopted as a safe and highly stable (co)solvent for zinc (Zn) batteries, which affords excellent compatibility with the Zn anode. A cycle life of over 5000 h for Zn/Zn symmetric cells with an average Coulombic efficiency of 99.57%, accompanied by a dendrite‐free graphene‐analogous morphology are the key outcomes of this work. Abstract Dendrite and interfacial reactions have affected zinc (Zn) metal anodes for rechargeable batteries many years. Here, these obstacles are bypassed via adopting an intrinsically safe trimethyl phosphate (TMP)‐based electrolyte to build a stable Zn anode. Along with cycling, pristine Zn foil is gradually converted to a graphene‐analogous deposit via TMP surfactant and a Zn phosphate molecular template. This novel Zn anode morphology ensures long‐term reversible plating/stripping performance over 5000 h, a rate capability of 5 mA cm−2, and a remarkably high Coulombic efficiency (CE) of ≈99.57% without dendrite formation. As a proof‐of‐concept, a Zn–VS2 full cell demonstrates an ultralong lifespan, which provides an alternative for electrochemical energy storage devices.

Published in: "Advanced Materials".

One‐Step Synthesis of 2‐Ethylhexylamine Pillared Vanadium Disulfide Nanoflowers with Ultralarge Interlayer Spacing for High‐Performance Magnesium Storage

2019-06-20T17:06:28+00:00June 20th, 2019|Categories: Publications|Tags: , |

2‐Ethylhexylamine pillared VS2 nanoflowers with ultralarge interlayer spacing are prepared by a one‐pot solvothermal method with 2‐ethylhexylamine serving as the reaction medium and intercalant. The 2‐ethylhexylamine enlarges the ionic channels and shields the Coulombic interactions between active Mg species and hosts, boosting the ion transport. Moreover, the presence of 2‐ethylhexylamine as pillars is beneficial to the integrity of hosts, contributing to the long lifespan. Abstract Rechargeable magnesium batteries (RMBs) are attractive candidates for large‐scale energy storage owing to the high theoretical specific capacity, rich earth abundance, and good safety characteristics. However, the development of desirable cathode materials for RMBs is constrained by the high polarity and slow intercalation kinetics of Mg2+ ions. Herein, it is demonstrated that 2‐ethylhexylamine pillared vanadium disulfide nanoflowers (expanded VS2) with enlarged interlayer distances exhibit greatly boosted electrochemical performance as a cathode material in RMBs. Through a one‐step solution‐phase synthesis and in situ 2‐ethylhexylamine intercalation process, VS2 nanoflowers with ultralarge interlayer spacing are prepared. A series of ex situ characterizations verify that the cathode of expanded VS2 nanoflowers undergoes a reversible intercalation reaction mechanism, followed by a conversion reaction mechanism. Electrochemical kinetics analysis reveal a relatively fast Mg‐ion diffusivity of expanded VS2 nanoflowers in the order of 10−11–10−12 cm2 s−1, and the pseudocapacitive contribution is up to 64% for the total capacity at 1 mV s−1. The expanded VS2 nanoflowers show highly reversible discharge capacity (245 mAh g−1 at 100 mA g−1), good rate capability (103 mAh g−1 at 2000 mA g−1), and stable cycling performance

Published in: "Advanced Energy Materials".

One‐Step Synthesis of 2‐Ethylhexylamine Pillared Vanadium Disulfide Nanoflowers with Ultralarge Interlayer Spacing for High‐Performance Magnesium Storage

2019-06-15T23:01:34+00:00June 15th, 2019|Categories: Publications|Tags: , |

2‐Ethylhexylamine pillared VS2 nanoflowers with ultralarge interlayer spacing are prepared by a one‐pot solvothermal method with 2‐ethylhexylamine serving as the reaction medium and intercalant. The 2‐ethylhexylamine enlarges the ionic channels and shields the Coulombic interactions between active Mg species and hosts, boosting the ion transport. Moreover, the presence of 2‐ethylhexylamine as pillars is beneficial to the integrity of hosts, contributing to the long lifespan. Abstract Rechargeable magnesium batteries (RMBs) are attractive candidates for large‐scale energy storage owing to the high theoretical specific capacity, rich earth abundance, and good safety characteristics. However, the development of desirable cathode materials for RMBs is constrained by the high polarity and slow intercalation kinetics of Mg2+ ions. Herein, it is demonstrated that 2‐ethylhexylamine pillared vanadium disulfide nanoflowers (expanded VS2) with enlarged interlayer distances exhibit greatly boosted electrochemical performance as a cathode material in RMBs. Through a one‐step solution‐phase synthesis and in situ 2‐ethylhexylamine intercalation process, VS2 nanoflowers with ultralarge interlayer spacing are prepared. A series of ex situ characterizations verify that the cathode of expanded VS2 nanoflowers undergoes a reversible intercalation reaction mechanism, followed by a conversion reaction mechanism. Electrochemical kinetics analysis reveal a relatively fast Mg‐ion diffusivity of expanded VS2 nanoflowers in the order of 10−11–10−12 cm2 s−1, and the pseudocapacitive contribution is up to 64% for the total capacity at 1 mV s−1. The expanded VS2 nanoflowers show highly reversible discharge capacity (245 mAh g−1 at 100 mA g−1), good rate capability (103 mAh g−1 at 2000 mA g−1), and stable cycling performance

Published in: "Advanced Energy Materials".

One‐Step Synthesis of 2‐Ethylhexylamine Pillared Vanadium Disulfide Nanoflowers with Ultralarge Interlayer Spacing for High‐Performance Magnesium Storage

2019-06-15T23:01:35+00:00June 15th, 2019|Categories: Publications|Tags: , |

2‐Ethylhexylamine pillared VS2 nanoflowers with ultralarge interlayer spacing are prepared by a one‐pot solvothermal method with 2‐ethylhexylamine serving as the reaction medium and intercalant. The 2‐ethylhexylamine enlarges the ionic channels and shields the Coulombic interactions between active Mg species and hosts, boosting the ion transport. Moreover, the presence of 2‐ethylhexylamine as pillars is beneficial to the integrity of hosts, contributing to the long lifespan. Abstract Rechargeable magnesium batteries (RMBs) are attractive candidates for large‐scale energy storage owing to the high theoretical specific capacity, rich earth abundance, and good safety characteristics. However, the development of desirable cathode materials for RMBs is constrained by the high polarity and slow intercalation kinetics of Mg2+ ions. Herein, it is demonstrated that 2‐ethylhexylamine pillared vanadium disulfide nanoflowers (expanded VS2) with enlarged interlayer distances exhibit greatly boosted electrochemical performance as a cathode material in RMBs. Through a one‐step solution‐phase synthesis and in situ 2‐ethylhexylamine intercalation process, VS2 nanoflowers with ultralarge interlayer spacing are prepared. A series of ex situ characterizations verify that the cathode of expanded VS2 nanoflowers undergoes a reversible intercalation reaction mechanism, followed by a conversion reaction mechanism. Electrochemical kinetics analysis reveal a relatively fast Mg‐ion diffusivity of expanded VS2 nanoflowers in the order of 10−11–10−12 cm2 s−1, and the pseudocapacitive contribution is up to 64% for the total capacity at 1 mV s−1. The expanded VS2 nanoflowers show highly reversible discharge capacity (245 mAh g−1 at 100 mA g−1), good rate capability (103 mAh g−1 at 2000 mA g−1), and stable cycling performance

Published in: "Advanced Energy Materials".

Novel single-layer vanadium sulphide phases. (arXiv:1803.07999v1 [cond-mat.mtrl-sci])

2018-03-22T19:59:15+00:00March 22nd, 2018|Categories: Publications|Tags: , |

VS2 is a challenging material to prepare stoichiometrically in the bulk, and the single layer has not been successfully isolated before now. Here we report the first realization of single-layer VS2, which we have prepared epitaxially with high quality on Au(111) in the octahedral (1T) structure. We find that we can deplete the VS2 lattice of S by annealing in vacuum so as to create an entirely new two-dimensional compound that has no bulk analogue. The transition is reversible upon annealing in an H2S gas atmosphere. We report the structural properties of both the stoichiometric and S-depleted compounds on the basis of low-energy electron diffraction, X-ray photoelectron spectroscopy and diffraction, and scanning tunneling microscopy experiments.

Published in: "arXiv Material Science".

Graphene publications, patents and news are copyrighted by their respective owner. Editorial posts and everything else, copyright 2012-2017 2D Research.
FacebookTwitterRssLinkedInEmail
Toggle Sliding Bar Area
Some say, that 2D Research is the best website in the world.