/Tag: MoS2

Probing photoresponse of aligned single-walled carbon nanotube doped ultrathin MoS 2

2018-06-19T12:33:37+00:00 June 19th, 2018|Categories: Publications|Tags: , |

We report a facile method to produce ultrathin molybdenum disulfide (MoS 2 ) hybrids with polarized near-infrared (NIR) photoresponses, in which horizontally-aligned single-walled carbon nanotubes (SWNTs) are integrated with single- and few-layer MoS 2 through a two-step chemical vapor deposition process. The photocurrent generation mechanisms in SWNT-MoS 2 hybrids are systematically investigated through wavelength- and polarization-dependent scanning photocurrent measurements. When the incident photon energy is above the direct bandgap of MoS 2 , isotropic photocurrent signals are observed, which can be primarily attributed to the direct bandgap transition in MoS 2 . In contrast, if the incident photon energy in the NIR region is below the direct bandgap of MoS 2 , the maximum photocurrent response occurs when the incident light is polarized in the direction along the SWNTs, indicating that photocurrent signals mainly resu…

Published in: "Nanotechnology".

Interactions and magnetotransport through spin-valley coupled Landau levels in monolayer MoS$_{2}$. (arXiv:1806.06402v1 [cond-mat.mes-hall])

2018-06-19T04:30:27+00:00 June 19th, 2018|Categories: Publications|Tags: , |

The strong spin-orbit coupling and the broken inversion symmetry in monolayer transition metal dichalcogenides (TMDs) results in spin-valley coupled band structures. Such a band structure leads to novel applications in the fields of electronics and optoelectronics. Density functional theory calculations as well as optical experiments have focused on spin-valley coupling in the valence band. Here we present magnetotransport experiments on high-quality n-type monolayer molybdenum disulphide (MoS$_{2}$) samples, displaying highly resolved Shubnikov-de Haas oscillations at magnetic fields as low as $2~T$. We find the effective mass $0.7~m_{e}$, about twice as large as theoretically predicted and almost independent of magnetic field and carrier density. We further detect the occupation of the second spin-orbit split band at an energy of about $15~meV$, i.e. about a factor $5$ larger than predicted. In addition, we demonstrate an intricate Landau level spectrum arising from a complex interplay between a density-dependent Zeeman splitting and spin and valley-split Landau levels. These observations, enabled by the high electronic quality of our samples, testify to the importance of interaction effects in the conduction band of monolayer MoS$_{2}$.

Published : "arXiv Mesoscale and Nanoscale Physics".

Extraction of Intrinsic Electrical Parameters in Partially Depleted MoS<sub>2</sub> Field-Effect Transistors

2018-06-19T00:34:07+00:00 June 19th, 2018|Categories: Publications|Tags: |

Electrical performance and transport mechanisms in 2-D transition-metal dichalcogenide materials should be investigated under a range of electrical parameters for practical application. In this paper, partially depleted (PD) molybdenum disulfide (MoS2) transistors were fabricated with a thick flake mechanically exfoliated from bulk crystals, and their operating mechanism is discussed considering the gate-uncontrollable conduction channel, the maximum depletion width (${D}_{mathrm {text {max}}}$ ), and the impact of series resistance (${R}_{mathrm {text {sd}}}$ ). In addition, the intrinsic mobility of a neutral bulk channel in PD-MoS2 transistors was extracted from the simply separated gate-controllable drain current with a depletion approximation.

Published in: "IEEE Transactions on Electron Devices".

Interlayer coupling and the phase transition mechanism of stacked MoS2/TaS2 heterostructures discovered using temperature dependent Raman and photoluminescence spectroscopy

2018-06-14T14:32:24+00:00 June 14th, 2018|Categories: Publications|Tags: , , , |

RSC Adv., 2018, 8,21968-21974DOI: 10.1039/C8RA03436B, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Miao Chen, Bin Zhou, Fang Wang, Liping Xu, Kai Jiang, Liyan Shang, Zhigao Hu, Junhao ChuThe important interlayer coupling of the MoS2-TaS2 heterostructure

Published in: "RSC Advances".

Approaching perfect absorption of monolayer molybdenum disulfide at visible wavelengths using critical coupling

2018-06-13T12:33:39+00:00 June 13th, 2018|Categories: Publications|Tags: |

A simple perfect absorption structure is proposed to achieve the high efficiency light absorption of monolayer molybdenum disulfide (MoS 2 ) by the critical coupling mechanism of guided resonances. The results of numerical simulation and theoretical analysis show that the light absorption in this atomically thin layer can be as high as 98.3% at the visible wavelengths, which is over 12 times more than that of a bare monolayer MoS 2 . In addition, the operating wavelength can be tuned flexibly by adjusting the radius of the air hole and the thickness of the dielectric layers, which is of great practical significance to improve the efficiency and selectivity of the absorption in monolayer MoS 2 . The novel idea of using critical coupling to enhance the light-MoS 2 interaction can be also adopted in other atomically thin materials. The meaningful improvement and tunability of the absorption in monolayer MoS 2 provides a good prospect f…

Published in: "Nanotechnology".

Preparation of MoS2-based polydopamine-modified core-shell nanocomposites with elevated adsorption performances

2018-06-13T10:32:19+00:00 June 13th, 2018|Categories: Publications|Tags: |

RSC Adv., 2018, 8,21644-21650DOI: 10.1039/C8RA02964D, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.Shuxin Sun, Tifeng Jiao, Ruirui Xing, Jinghong Li, Jingxin Zhou, Lexin Zhang, Qiuming PengNew core-shell MoS2-PDA nanocomposites are prepared via mussel-inspired chemistry and

Published in: "RSC Advances".

Phase-Modulated Degenerate Parametric Amplification Microscopy. (arXiv:1806.03493v1 [physics.optics])

2018-06-12T02:29:16+00:00 June 12th, 2018|Categories: Publications|Tags: |

Second-order nonlinear optical interactions, including second harmonic generation (SHG) and sum-frequency generation (SFG), can reveal a wealth of information about chemical, electronic, and vibrational dynamics at the nanoscale. Here, we demonstrate a powerful and flexible new approach, called phase-modulated degenerate parametric amplification (DPA). The technique, which allows for facile retrieval of both the amplitude and phase of the second-order nonlinear optical response, has many advantages over conventional or heterodyne-detected SHG, including the flexibility to detect the signal at either the second harmonic or fundamental field wavelength. We demonstrate the capabilities of this approach by imaging multi-grain flakes of single-layer MoS2. We identify the absolute crystal orientation of each MoS2 domain and resolve grain boundaries with high signal contrast and sub-diffraction-limited spatial resolution. This robust all-optical method can be used to characterize structure and dynamics in organic and inorganic systems, including biological tissue, soft materials, and metal and semiconductor nanostructures, and is particularly well-suited for imaging in media that are absorptive or highly scattering to visible and ultraviolet light.

Published in: "arXiv Material Science".

Comparison of trapped charges and hysteresis behavior in hBN encapsulated single MoS 2 flake based field effect transistors on SiO 2 and hBN substrates

2018-06-11T10:33:10+00:00 June 11th, 2018|Categories: Publications|Tags: , |

Molybdenum disulfide (MoS 2 ) based field effect transistors (FETs) are of considerable interest in electronic and opto-electronic applications but often have large hysteresis and threshold voltage instabilities. In this study, by using advanced transfer techniques, hexagonal boron nitride (hBN) encapsulated FETs based on a single, homogeneous and atomic-thin MoS 2 flake are fabricated on hBN and SiO 2 substrates. This allows for a better and a precise comparison between the charge traps at the semiconductor-dielectric interfaces at MoS 2 −SiO 2 and hBN interfaces. The impact of ambient environment and entities on hysteresis is minimized by encapsulating the active MoS 2 layer with a single hBN on both the devices. The device to device variations induced by different MoS 2 layer is also eliminated by employing a single MoS 2 layer for fabricating both devices. After eliminating these additional factors…

Published in: "Nanotechnology".

Interface Dipole and Band Bending in Hybrid p-n Heterojunction MoS2/GaN(0001). (arXiv:1806.03056v1 [cond-mat.mtrl-sci])

2018-06-11T02:29:41+00:00 June 11th, 2018|Categories: Publications|Tags: , |

Hybrid heterostructures based on bulk GaN and two-dimensional (2D) materials offer novel paths toward nanoelectronic devices with engineered features. Here, we study the electronic properties of a mixed-dimensional heterostructure composed of intrinsic n-doped MoS2 flakes transferred on p-doped GaN(0001) layers. Based on angle-resolved photoemission spectroscopy (ARPES) and high resolution X-ray photoemission spectroscopy (HR-XPS), we investigate the electronic structure modification induced by the interlayer interactions in MoS2/GaN heterostructure. In particular, a shift of the valence band with respect to the Fermi level for MoS2/GaN heterostructure is observed; which is the signature of a charge transfer from the 2D monolayer MoS2 to GaN. ARPES and HR-XPS revealed an interface dipole associated with local charge transfer from the GaN layer to the MoS2 monolayer. Valence and conduction band offsets between MoS2 and GaN are determined to be 0.77 and -0.51 eV, respectively. Based on the measured work functions and band bendings, we establish the formation of an interface dipole between GaN and MoS2 of 0.2 eV.

Published in: "arXiv Material Science".

Tunable Doping in Hydrogenated Single Layered Molybdenum Disulfide. (arXiv:1806.02655v1 [cond-mat.mtrl-sci])

2018-06-08T02:29:15+00:00 June 8th, 2018|Categories: Publications|Tags: |

Structural defects in the molybdenum disulfide (MoS2) monolayer are widely known for strongly altering its properties. Therefore, a deep understanding of these structural defects and how they affect MoS2 electronic properties is of fundamental importance. Here, we report on the incorporation of atomic hydrogen in mono-layered MoS2 to tune its structural defects. We demonstrate that the electronic properties of single layer MoS2 can be tuned from the intrinsic electron (n) to hole (p) doping via controlled exposure to atomic hydrogen at room temperature. Moreover, this hydrogenation process represents a viable technique to completely saturate the sulfur vacancies present in the MoS2 flakes. The successful incorporation of hydrogen in MoS2 leads to the modification of the electronic properties as evidenced by high resolution X-ray photoemission spectroscopy and density functional theory calculations. Micro-Raman spectroscopy and angle resolved photoemission spectroscopy measurements show the high quality of the hydrogenated MoS2 confirming the efficiency of our hydrogenation process. These results demonstrate that the MoS2 hydrogenation could be a significant and efficient way to achieve tunable doping of transition metal dichalcogenides (TMD) materials with non-TMD elements.

Published in: "arXiv Material Science".

Dielectric properties of graphene/${mathrm{MoS}}_{2}$ heterostructures from <i>ab initio</i> calculations and electron energy-loss experiments

2018-06-07T16:33:23+00:00 June 7th, 2018|Categories: Publications|Tags: , , , |

Author(s): Michael J. Mohn, Ralf Hambach, Philipp Wachsmuth, Christine Giorgetti, and Ute KaiserHigh-energy electronic excitations of graphene and MoS2 heterostructures are investigated by momentum-resolved electron energy-loss spectroscopy in the range of 1 to 35 eV. The interplay of excitations on different sheets is understood in terms of long-range Coulomb interactions and is simulated usi…[Phys. Rev. B 97, 235410] Published Thu Jun 07, 2018

Published in: "Physical Review B".

Intrinsic properties of suspended MoS2 on SiO2/Si pillar arrays for nanomechanics and optics. (arXiv:1806.02241v1 [cond-mat.mes-hall])

2018-06-07T04:30:17+00:00 June 7th, 2018|Categories: Publications|Tags: |

Semiconducting 2D materials, such as transition metal dichalcogenides (TMDs), are emerging in nanomechanics, optoelectronics, and thermal transport. In each of these fields, perfect control over 2D material properties including strain, doping, and heating is necessary, especially on the nanoscale. Here, we study clean devices consisting of membranes of single-layer MoS2 suspended on pillar arrays. Using Raman and photoluminescence spectroscopy, we have been able to extract, separate and simulate the different contributions on the nanoscale and to correlate these to the pillar array design. This control has been used to design a periodic MoS2 mechanical membrane with a high reproducibility and to perform optomechanical measurements on arrays of similar resonators with a high-quality factor of 600 at ambient temperature, hence opening the way to multi-resonator applications with 2D materials. At the same time, this study constitutes a reference for the future development of well-controlled optical emissions within 2D materials on periodic arrays with reproducible behavior. We measured a strong reduction of the MoS2 band-gap induced by the strain generated from the pillars. A transition from direct to indirect band gap was observed in isolated tent structures made of MoS2 and pinched by a pillar. In fully suspended devices, simulations were performed allowing both the extraction of the thermal conductance and doping of the layer. Using the correlation between the influences of strain and doping on the MoS2 Raman spectrum, we have developed a simple, elegant method to extract the local strain in suspended and non-suspended parts of a membrane. This opens

Published : "arXiv Mesoscale and Nanoscale Physics".

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