/Tag: MoS2

Defect sizing, separation, and substrate effects in ion-irradiated monolayer two-dimensional materials

2018-10-18T14:33:24+00:00 October 18th, 2018|Categories: Publications|Tags: , |

Author(s): Pierce Maguire, Daniel S. Fox, Yangbo Zhou, Qianjin Wang, Maria O’Brien, Jakub Jadwiszczak, Conor P. Cullen, John McManus, Samuel Bateman, Niall McEvoy, Georg S. Duesberg, and Hongzhou ZhangPrecise and scalable defect engineering of two-dimensional (2D) nanomaterials is acutely sought after in contemporary materials science. Here, we present defect engineering in monolayer graphene and molybdenum disulfide (MoS2) by irradiation with noble gas ions at 30 keV. Two ion species of differen…[Phys. Rev. B 98, 134109] Published Thu Oct 18, 2018

Published in: "Physical Review B".

Use of a diatomite template to prepare a MoS2/amorphous carbon composite and exploration of its electrochemical properties as a supercapacitor

2018-10-18T08:34:42+00:00 October 18th, 2018|Categories: Publications|Tags: , |

RSC Adv., 2018, 8,35672-35680DOI: 10.1039/C8RA07062H, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Yang Yang, Aijun Li, Xi Cao, Fangfang Liu, Siyu Cheng, Xiuyun ChuanAmorphous carbon is partially inserted into the interlayer spaces of MoS2 in

Published in: "RSC Advances".

Tuning Bandgap and Energy Stability of Organic-Inorganic Halide Perovskites through Surface Engineering. (arXiv:1810.07297v1 [])

2018-10-18T02:29:28+00:00 October 18th, 2018|Categories: Publications|Tags: , , , , , , |

Organohalide perovskite with a variety of surface structures and morphologies have shown promising potential owing to the choice of the type of heterostructure dependent stability. We systematically investigate and discuss the impact of 2-dimensional molybdenum-disulphide (MoS2), molybdenum-diselenide (MoSe2), tungsten-disulphide (WS2), tungsten-diselenide (WSe2), boron- nitiride (BN) and graphene monolayers on band-gap and energy stability of organic-inorganic halide perovskites. We found that MAPbI3ML deposited on BN-ML shows room temperature stability (-25 meV~300K) with an optimal bandgap of ~1.6 eV. The calculated absorption coefficient also lies in the visible-light range with a maximum of 4.9 x 104 cm-1 achieved at 2.8 eV photon energy. On the basis of our calculations, we suggest that the encapsulation of an organic-inorganic halide perovskite monolayers by semiconducting monolayers potentially provides greater flexibility for tuning the energy stability and the bandgap.

Published in: "arXiv Material Science".

An atomistic model for the charge distribution in layered MoS2. (arXiv:1810.07341v1 [cond-mat.mes-hall])

2018-10-18T02:29:24+00:00 October 18th, 2018|Categories: Publications|Tags: |

We present an atomistic model for predicting the distribution of doping electric charges in layered molybdenum disulfide (MoS$_{2}$). This model mimics the charge around each ion as a net Gaussian-spatially-distributed charge plus an induced dipole, and is able to predict the distribution of doping charges in layered MoS$_{2}$ in a self-consistent scheme. The profiles of doping charges in monolayer MoS$_{2}$ flakes computed by this charge-dipole model are in good agreement with those obtained by density-functional-theory calculations. Using this model, we quantitatively predict the charge enhancement effect in MoS$_{2}$ monolayer nanoribbons, with which strong ionic charge-localization effects are shown.

Published in: "arXiv Material Science".

In-situ fabrication of Mo6S6 nanowire terminated edges in monolayer molybdenum disulfide. (arXiv:1810.07467v1 [cond-mat.mtrl-sci])

2018-10-18T02:29:22+00:00 October 18th, 2018|Categories: Publications|Tags: |

Edge structures are highly relevant to the electronic, magnetic and catalytic properties of two-dimensional (2D) transition metal dichalcogenides (TMDs) and their one dimensional (1D) counterpart, i.e., nanoribbons, which should be precisely tailored for the desirable applications. In this work, we report the formation of novel Mo6S6 nanowire (NW) terminated edges in a monolayer molybdenum disulfide (MoS2) via an e-beam irradiation process combined with high temperature heating in a scanning transmission electron microscope (STEM). Atomic structures of NW terminated edges and the dynamic formation process were observed experimentally. Further analysis shows that NW terminated edge could form on both Mo-zigzag (ZZ) edge and S-ZZ edge which can exhibit even higher stability superior to the pristine zigzag (ZZ) and armchair (AC) edge. In addition, the analogous edge structures can be also formed in MoS2 nanoribbon and other TMDs material such as MoxW1-xSe2. We believe that the presence of these novel edge structures in 2D and 1D TMD materials may provide novel properties and new opportunities for their versatile applications including catalytic, spintronic and electronic devices.

Published in: "arXiv Material Science".

Phase-selective synthesis of 1T′ MoS<sub>2</sub> monolayers and heterophase bilayers

2018-10-15T16:39:02+00:00 October 15th, 2018|Categories: Publications|Tags: |

Phase-selective synthesis of 1T′ MoS2 monolayers and heterophase bilayersPhase-selective synthesis of 1T′ MoS<sub>2</sub> monolayers and heterophase bilayers, Published online: 15 October 2018; doi:10.1038/s41563-018-0187-1The 1T′ phase of MoS2 monolayers, as well as the 2H phase and their heterophase bilayers, can be grown directly by tuning the potassium concentration in the reaction atmosphere. The pure 1T′ phase demonstrates in-plane anisotropic properties.

Published in: "Nature Materials".

MoS2-Quantum Dots Triggered Reactive Oxygen Species Generation and Depletion: Responsible for Enhanced Chemiluminescence

2018-10-15T14:32:26+00:00 October 15th, 2018|Categories: Publications|Tags: |

Chem. Sci., 2019, Accepted ManuscriptDOI: 10.1039/C8SC03511C, Edge Article Open Access &nbsp This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.Xiangnan Dou, Qiang Zhang, Syed Niaz Ali Shah, Mashooq Khan, Katsumi Uchiyama, Jin-Ming LinReactive oxygen species (ROS) generation is of intense interest because of its crucial role in many fields. Here we demonstrate MoS2-QDs exhibits a promising capability for generation of reactive oxygen…The content of this RSS Feed (c) The Royal Society of Chemistry

Published in: "Chemical Science".

Epoxy composites with functionalized molybdenum disulfide nanoplatelet additives

2018-10-15T08:32:32+00:00 October 15th, 2018|Categories: Publications|Tags: , |

RSC Adv., 2018, 8,35170-35178DOI: 10.1039/C8RA07448H, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Ming Zhao, Lizhu Liu, Bin Zhang, Mingming Sun, Xugang Zhang, Xue Zhang, Jianhui Li, Lei WangAs a typical layered inorganic analogue of graphene,

Published in: "RSC Advances".

Contactless photo-induced carrier density control in nanocrystal MoS2 hybrids. (arXiv:1810.05385v1 [cond-mat.mes-hall])

2018-10-15T04:30:22+00:00 October 15th, 2018|Categories: Publications|Tags: , |

The ultrathin nature of two-dimensional monolayer semiconductors yields optoelectronic properties which are highly responsive to changes in free-carrier density, making it imperative to masterfully control their doping levels. We report a new photo-doping scheme that quasi-permanently dopes the monolayer MoS2 to extents competing with electrostatic gating. The photo-doping is achieved by coupling monolayer MoS2 with indium tin oxide nanocrystals that can store multiple electrons per nanocrystal after UV illumination. In the hybrid structure, the photo-generated valence band holes in the nanocrystals are filled by MoS2 electrons, photo-doping the MoS2 with holes. Reductions in carrier density by ~6×10^12 cm^-2 are observed, equivalent to the storage of ~40 electrons per nanocrystal. Long-range changes proliferating up to 40 micrometers away from the localized photodoping result from local bandstructure variations in MoS2. These studies reveal novel all-optical carrier density control in monolayer semiconductors, enabling remote-control of local charge density and innovative energy storage technologies.

Published : "arXiv Mesoscale and Nanoscale Physics".

Negative electronic compressibility and nanoscale inhomogeneity in ionic-liquid gated two-dimensional superconductors. (arXiv:1706.01274v2 [cond-mat.mes-hall] UPDATED)

2018-10-12T04:30:18+00:00 October 12th, 2018|Categories: Publications|Tags: , |

When the electron density of highly crystalline thin films is tuned by chemical doping or ionic liq- uid gating, interesting effects appear including unconventional superconductivity, sizeable spin-orbit coupling, competition with charge-density waves, and a debated low-temperature metallic state that seems to avoid the superconducting or insulating fate of standard two-dimensional electron systems. Some experiments also find a marked tendency to a negative electronic compressibility. We suggest that this indicates an inclination for electronic phase separation resulting in a nanoscopic inhomo- geneity. Although the mild modulation of the inhomogeneous landscape is compatible with a high electron mobility in the metallic state, this intrinsically inhomogeneous character is highlighted by the peculiar behaviour of the metal-to-superconductor transition. Modelling the system with super- conducting puddles embedded in a metallic matrix, we fit the peculiar resistance vs. temperature curves of systems like TiSe2, MoS2, and ZrNCl. In this framework also the low-temperature debated metallic state finds a natural explanation in terms of the pristine metallic background embedding non-percolating superconducting clusters. An intrinsically inhomogeneous character naturally raises the question of the formation mechanism(s). We propose a mechanism based on the interplay be- tween electrons and the charges of the gating ionic liquid.

Published : "arXiv Mesoscale and Nanoscale Physics".

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2. (arXiv:1810.04745v1 [cond-mat.mtrl-sci])

2018-10-12T02:29:42+00:00 October 12th, 2018|Categories: Publications|Tags: , , , , |

The research field of two dimensional (2D) materials strongly relies on optical microscopy characterization tools to identify atomically thin materials and to determine their number of layers. Moreover, optical microscopy-based techniques opened the door to study the optical properties of these nanomaterials. We presented a comprehensive study of the differential reflectance spectra of 2D semiconducting transition metal dichalcogenides (TMDCs), MoS2, MoSe2, WS2, and WSe2, with thickness ranging from one layer up to six layers. We analyzed the thickness-dependent energy of the different excitonic features, indicating the change in the band structure of the different TMDC materials with the number of layers. Our work provided a route to employ differential reflectance spectroscopy for determining the number of layers of MoS2, MoSe2, WS2, and WSe2.

Published in: "arXiv Material Science".

Structural, electronic, vibrational, and elastic properties of graphene/${mathrm{MoS}}_{2}$ bilayer heterostructures

2018-10-11T14:32:41+00:00 October 11th, 2018|Categories: Publications|Tags: , , |

Author(s): Sobhit Singh, Camilo Espejo, and Aldo H. RomeroGraphene/MoS2 van der Waals (vdW) heterostructures have promising technological applications due to their unique properties and functionalities. Many experimental and theoretical research groups across the globe have made outstanding contributions to benchmark the properties of graphene/MoS2 heteros…[Phys. Rev. B 98, 155309] Published Thu Oct 11, 2018

Published in: "Physical Review B".

Analyzing the Effect of High-k Dielectric-Mediated Doping on Contact Resistance in Top-Gated Monolayer MoS<sub>2</sub> Transistors

2018-10-09T00:33:09+00:00 October 9th, 2018|Categories: Publications|Tags: |

A scalable process that can yield low-resistance contacts to transition metal dichalcogenides is crucial for realizing a viable device technology from these materials. Here, we systematically examine the effect of high-k dielectric-mediated doping on key device metrics including contact resistance and carrier mobility. Specifically, we use top-gated transistors from monolayer MoS2 as a test vehicle and vary the MoS2 doping level by adjusting the amount of oxygen vacancies in the HfOx gate dielectric. To understand the effect of doping on the contact resistance, from a fundamental standpoint, we first estimate the doping level in monolayer MoS2. The results of our device studies quantitatively show that the reduction in contact resistance with an increase in doping is due to the doping-induced lowering of the Schottky barrier height (SBH) at the metal-semiconductor interface. Furthermore, our temperature-dependent measurements reveal that a mixture of thermionic and field emissions, even at high carrier densities, dominates carrier conduction at the contact. While our study reveals the effectiveness of dielectric-induced doping in lowering SBH, it suggests that a further reduction of SBH using alternative methods is necessary for achieving an ohmic-like contact to monolayer MoS2.

Published in: "IEEE Transactions on Electron Devices".

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