/Tag: MoS2

Picosecond transient thermoreflectance technique for measuring thermal conductivity in thin-films. (arXiv:1808.04972v1 [cond-mat.mtrl-sci])

2018-08-16T02:29:19+00:00 August 16th, 2018|Categories: Publications|Tags: |

We have developed a transient thermoreflectance technique using picosecond pulsed and cw laser to study thermal conductivity and interface conductance in both thin-films and bulk materials. A real time-resolved system observes a thermal transport along the cross-plane direction of the sample during a single pulse excitation. The suggested TTR technique can measure thermal conductivity in up to a few hundred nm of thin films with a reasonable uncertainty by carefully selecting metal transducer thickness. In this paper, we examine thermal conductivity in several substrates including Si, GaAs, Sapphire, and Glass after depositing Au thin film as metal transducer and compare with reported values to validate our technique. For further study on our method, MoS2 thin-films with different thicknesses are prepared via exfoliating, and their thermal conductivity are measured as average value of 3.4 W/mK. Compared to TDTR technique, TTR is a simpler and inexpensive method to study thermophysical properties and can also measure in-plane thermal property using a grating imaging technique. TTR can be one of the available options for observing thermal transport phenomena in both horizontal and vertical directions with a simple and inexpensive preparation.

Published in: "arXiv Material Science".

Femtosecond valley polarization and topological resonances in transition metal dichalcogenides

2018-08-15T16:33:21+00:00 August 15th, 2018|Categories: Publications|Tags: , |

Author(s): S. Azar Oliaei Motlagh, Jhih-Sheng Wu, Vadym Apalkov, and Mark I. StockmanWe theoretically introduce the fundamentally fastest induction of a significant population and valley polarization in a monolayer of a transition metal dichalcogenide (i.e., MoS2 and WS2). This may be extended to other two-dimensional materials with the same symmetry. This valley polarization can be…[Phys. Rev. B 98, 081406(R)] Published Wed Aug 15, 2018

Published in: "Physical Review B".

Intrinsic Point Defects in Ultrathin 1T-PtSe2 Layers. (arXiv:1808.04719v1 [cond-mat.mes-hall])

2018-08-15T04:30:22+00:00 August 15th, 2018|Categories: Publications|Tags: , , |

Among two dimensional (2D) transition metal dichalcogenides (TMDs), platinum diselenide (PtSe2) stands at a unique place in the sense that it undergoes a phase transition from type-II Dirac semimetal to indirect-gap semiconductor as thickness decreases. Defects in 2D TMDs are ubiquitous and they play crucial roles in understanding electronic, optical, and magnetic properties and tailoring them for desirable applications. Here we investigate intrinsic point defects in ultrathin 1T-PtSe2 layers grown on mica through the chemical vapor transport method, using scanning tunneling microscopy (STM) and first-principles calculations. We found five distinct defects from STM topography images and obtained the local density of states of the defects. By combining the STM results with the first-principles calculations, we identified the types and characteristics of these defects, which are Pt vacancies at the topmost and next monolayers, Se vacancies in the topmost monolayer, and Se antisites at Pt sites within the topmost monolayer. Interestingly, our study shows that the Se antisite defects are the most abundant with the lowest formation energy in a Se-rich growth condition, in contrast to cases of 2D TMD MoS2 family. Our findings will directly influence tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering or growth condition in thin semiconductor PtSe2 layers.

Published : "arXiv Mesoscale and Nanoscale Physics".

Carboxymethylcellulose ammonium-derived nitrogen-doped carbon fiber/molybdenum disulfide hybrids for high-performance supercapacitor electrodes

2018-08-14T10:33:18+00:00 August 14th, 2018|Categories: Publications|Tags: , |

RSC Adv., 2018, 8,28944-28952DOI: 10.1039/C8RA04492A, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Yanyan Lv, Yi Zhou, Ziqiang Shao, Jie Wei, Lei Li, Yiping WangNovel CMC-NH4-derived nitrogen-doped CFs/MoS2 hybrid electrode materials are prepared using CMC-NH4 as

Published in: "RSC Advances".

Asymmetric Schottky Contacts in Bilayer MoS2 Field Effect Transistors. (arXiv:1808.02119v1 [cond-mat.mes-hall])

2018-08-08T04:30:20+00:00 August 8th, 2018|Categories: Publications|Tags: |

We discuss the high-bias electrical characteristics of back-gated field-effect transistors with CVD-synthesized bilayer MoS2 channel and Ti Schottky contacts. We find that oxidized Ti contacts on MoS2 form rectifying junctions with ~0.3 to 0.5 eV Schottky barrier height. To explain the rectifying output characteristics of the transistors, we propose a model based on two slightly asymmetric back-to-back Schottky barriers, where the highest current arises from image force barrier lowering at the electrically forced junction, while the reverse current is due to Schottky-barrier limited injection at the grounded junction. The device achieves a photo responsivity greater than 2.5 AW-1 under 5 mWcm-2 white-LED light. By comparing two- and four-probe measurements, we demonstrate that the hysteresis and persistent photoconductivity exhibited by the transistor are peculiarities of the MoS2 channel rather than effects of the Ti/MoS2 interface.

Published : "arXiv Mesoscale and Nanoscale Physics".

Self-powered, high response and fast response speed metal–insulator–semiconductor structured photodetector based on 2D MoS2

2018-08-06T10:33:13+00:00 August 6th, 2018|Categories: Publications|Tags: |

RSC Adv., 2018, 8,28041-28047DOI: 10.1039/C8RA05511D, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.Xinxin Liu, Feng Li, Minxuan Xu, Junjie QiA MIS structured self-powered photodetector of Pd/HfO2/MoS2 was fabricated by inserting a thin insulator, which has

Published in: "RSC Advances".

Effect of Electron Irradiation on the Transport and Field Emission Properties of Few-Layer MoS2 Field Effect Transistors. (arXiv:1808.01185v1 [])

2018-08-06T00:30:19+00:00 August 6th, 2018|Categories: Publications|Tags: |

Electrical characterization of few-layer MoS2 based field effect transistors with Ti/Au electrodes is performed in the vacuum chamber of a scanning electron microscope in order to study the effects of electron beam irradiation on the transport properties of the device. A negative threshold voltage shift and a carrier mobility enhancement is observed and explained in terms of positive charges trapped in the SiO2 gate oxide, during the irradiation. The transistor channel current is increased up to three order of magnitudes after the exposure to an irradiation dose of 100e-/nm2. Finally, a complete field emission characterization of the MoS2 flake, achieving emission stability for several hours and a minimum turn-on field of about 20 V/um with a field enhancement factor of about 500 at anode-cathode distance of 1.5um, demonstrates the suitability of few-layer MoS2 as two-dimensional emitting surface for cold-cathode applications.

Published : "arXiv Mesoscale and Nanoscale Physics".

Observing the Phase Transformation of CVD-grown MoS2 via Atomic Resolution TEM

2018-08-03T04:33:34+00:00 August 3rd, 2018|Categories: Publications|Tags: |

Chem. Commun., 2018, Accepted ManuscriptDOI: 10.1039/C8CC05129A, CommunicationKuo-Lun Tai, Guan-Min Huang, Chun-Wei Huang, Tzung Chuen Tsai, Shih-Kuang Lee, Ting-Yi Lin, Yu-Chieh Lo, Wen-Wei WuWe utilized in-situ transmission electron microscopy to observe the phase transformation in CVD-grown MoS2. Significantly, the reaction was operated under electron irradiation through appropriate control of electron dose and exposure…The content of this RSS Feed (c) The Royal Society of Chemistry

Published in: "Chemical Communications".

Electronic transport and the related anomalous effects in silicene-like hexagonal lattice. (arXiv:1807.10898v1 [cond-mat.mtrl-sci])

2018-07-31T02:29:19+00:00 July 31st, 2018|Categories: Publications|Tags: , |

We investigate the anomalous effects due to the Berry correction and the considerable perturbations in the silicene-like hexagonal lattice system. The Berry curvature in periodic Bloch band system which related to the electromagnetic field is explored, the induced transverse anomalous velocity gives rise to the intrinsic Hall conductivity (without the vertex correction) expecially in the quantum anomalous Hall phase. The quantum anomalous Hall effect which related to the anomalous velocity term is detected, including the band avoided corssing effect and the generated special band gap. %{Enlarged Galilean symmetry of anyons and the Hall effect} The topological spin transport is affected by the Berry curvature %{Topological spin transport of a relativistic electron} %{Anomalous direction for skyrmion bubble motion} and the spin-current-induced Skyrmion spin texture motion is contrasted between the quantum spin Hall effect and quantum anomalous Hall effect. Since silicene involving the orbital degree of freedom, the orbital magnetic moment and orbital magnetization contributes significantly to the electronic transport properties of silicene %{Photoinduced quantum spin and valley Hall effects, and orbital magnetization in monolayer MoS2} as explored in this article. We also investigate the electronic tunneling properties of silicene in Josephon junction with the electric-field-induced Rashba-coupling, the anomalous effect due to the Berry phase is mentioned. Our results is meaningful to the application of the spintronics and valleytronics base on the silicene-like topological insulators.

Published in: "arXiv Material Science".

Large-Scale Conformal Growth of Atomic-Thick MoS2 for Highly Efficient Photocurrent Generation. (arXiv:1807.10433v1 [])

2018-07-30T02:29:17+00:00 July 30th, 2018|Categories: Publications|Tags: |

Controlling the interconnection of neighboring seeds (nanoflakes) to full coverage of the textured substrate is the main challenge for the large-scale conformal growth of atomic-thick transition metal dichalcogenides by chemical vapor deposition. Herein, we report on a controllable method for the conformal growth of monolayer MoS2 on not only planar but also micro- and nano-rugged SiO2/Si substrates via metal-organic chemical vapor deposition. The continuity of monolayer MoS2 on the rugged surface is evidenced by scanning electron microscopy, cross-section high-resolution transmission electron microscopy, photoluminescence (PL) mapping, and Raman mapping. Interestingly, the photo-responsivity (~254.5 mA/W) of as-grown MoS2 on the nano-rugged substrate exhibits 59 times higher than that of the planar sample (4.3 mA/W) under a small applied bias of 0.1 V. This value is record high when compared with all previous MoS2-based photocurrent generation under low or zero bias. Such a large enhancement in the photo-responsivity arises from a large active area for light-matter interaction and local strain for PL quenching, where the latter effect is the key factor and unique in the conformally grown monolayer on the nano-rugged surface. The result is a step toward the batch fabrication of modern atomic-thick optoelectronic devices.

Published in: "arXiv Material Science".

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