Giant gate-tunable bandgap renormalization and excitonic effects in a 2D semiconductor

2019-07-19T22:47:19+00:00July 19th, 2019|Categories: Publications|Tags: , |

Understanding the remarkable excitonic effects and controlling the exciton binding energies in two-dimensional (2D) semiconductors are crucial in unlocking their full potential for use in future photonic and optoelectronic devices. Here, we demonstrate large excitonic effects and gate-tunable exciton binding energies in single-layer rhenium diselenide (ReSe2) on a back-gated graphene

Published in: "Science Advances".

Manipulating the anomalous Josephson effect by interface valley-polarized mixing

2019-07-19T13:12:58+00:00July 19th, 2019|Categories: Publications|Tags: |

We theoretically investigate the supercurrent through a Josephson junction with at least one superconducting electrode directly coupled to a valley-polarized graphene sheet. The anomalous Josephson effect is shown and remarkably manipulated by interface valley-polarized mixing together with combination of the static staggered potentials and off-resonant circularly polarized light field inducing the valley polarization. The unconventional Josephson effect results from the breaking of underlying chiral (polarized-valley rotational) and time-reversal symmetries, which in turn shows the equivalence of the valley and spin freedoms. The valley-polarized interface-tunable phase offset will be of great interest in the designing and fabrication of such novel devices based on valleytronics as superconducting flux- and phase-based quantum bits, phase batteries and rectifiers.

Published in: "EPL".

Graphene surface contacts of tin disulfide transistors for switching performance improvement and contact resistance reduction

2019-07-19T09:06:19+00:00July 19th, 2019|Categories: Publications|Tags: , |

We investigated the performance improvement of tin disulfide channel transistors by graphene contact configurations. From its two-dimensional nature, graphene can make electric contacts only at the outermost layers of the channel. For intralayer current flow, two graphene flakes are contacted at the channel’s top or bottom layer. For interlayer current flow, one flake is contacted at the top and bottom of each layer. We compared the transistor performance in terms of current magnitude, mobility, and subthreshold swing between the configurations. From such observations, we deduced that device characteristics depend on resistivity or doping level of individual graphene flakes. We also found that interlayer flow excels in the on-current magnitude and the mobility, and that top-contact configuration excels in the subthreshold swing.

Published in: "Nanotechnology".

A uniform stable P-type graphene doping method with a gold etching process

2019-07-19T09:06:16+00:00July 19th, 2019|Categories: Publications|Tags: |

Graphene is one of the materials with the most potential for post-silicon electronics because of its outstanding electrical, optical, and mechanical properties. However, the lack of a uniform stable doping method extremely limits the various possible applications of graphene. Here, we developed a uniform and stable graphene efficient p-doping method. Through etching a thin gold film on graphene with a KI/I 2 solution, iodine complexes are produced as the dopant absorbing on the graphene surface, and induce extra holes in graphene. Utilizing this method, the graphene film can be effectively doped to p-type without producing undesirable defects, and the roughness of the graphene surface can still be maintained at an ultra-low nanoscale (RMS roughness ∼0.739 nm). The doping effectiveness can be clearly verified by the changes in the Raman spectrum, and the Dirac point shift of the graphene-based transistor, and the reduction of sheet resistance (∼27.2%). Furthermore, the …

Published in: "Nanotechnology".

Schottky barrier modulation of a GaTe/graphene heterostructure by interlayer distance and perpendicular electric field

2019-07-19T09:06:12+00:00July 19th, 2019|Categories: Publications|Tags: , , |

Two-dimensional materials have recently been the focus of extensive research. Graphene-based vertical van der Waals heterostructures are expected to design and fabricate novel electronic and optoelectronic devices. Monolayer gallium telluride is a graphene-like nanosheet synthesized in experiment. Here, the electronic properties of GaTe/graphene heterostructures are investigated under the interlayer coupling and the applied perpendicular electric field. The results show that the electronic properties of GaTe and graphene are preserved, and the energy bandgap of graphene is opened to 13.5 meV in the GaTe/graphene heterostructure. It is found that the n-type Schottky contact is formed in the GaTe/graphene heterostructure, which can be tuned by the interlayer coupling, and the applied electric field. Moreover, a transformation from n-type to p-type Schottky contact is observed when the interlayer distance is smaller than 3.15 Å or the applied electric field is larger than 0.05 V Å<…

Published in: "Nanotechnology".

Nitrogen doped small molecular structures of nano-graphene for high-performance anodes suitable for lithium ion storage

2019-07-19T08:49:59+00:00July 19th, 2019|Categories: Publications|Tags: |

RSC Adv., 2019, 9,22401-22409DOI: 10.1039/C9RA02498K, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Zhixiang Lv, Zhou Wang, Jianhong ChenN-doped nano-graphene derivatives were prepared by a bottom-up organic synthesis method.The content of this RSS Feed (c) The

Published in: "RSC Advances".

Nitrogen doped small molecular structures of nano-graphene for high-performance anodes suitable for lithium ion storage

2019-07-19T08:49:59+00:00July 19th, 2019|Categories: Publications|Tags: |

RSC Adv., 2019, 9,22401-22409DOI: 10.1039/C9RA02498K, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Zhixiang Lv, Zhou Wang, Jianhong ChenN-doped nano-graphene derivatives were prepared by a bottom-up organic synthesis method.The content of this RSS Feed (c) The

Published in: "RSC Advances".

Nitrogen doped small molecular structures of nano-graphene for high-performance anodes suitable for lithium ion storage

2019-07-19T08:49:59+00:00July 19th, 2019|Categories: Publications|Tags: |

RSC Adv., 2019, 9,22401-22409DOI: 10.1039/C9RA02498K, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Zhixiang Lv, Zhou Wang, Jianhong ChenN-doped nano-graphene derivatives were prepared by a bottom-up organic synthesis method.The content of this RSS Feed (c) The

Published in: "RSC Advances".

Unconventional electromagnetic properties of the graphene quantum dots. (arXiv:1907.08139v1 [cond-mat.mes-hall])

2019-07-19T04:34:40+00:00July 19th, 2019|Categories: Publications|Tags: , |

Quantum dots based on the graphene stripes show unconventional optical properties in the THz frequency range. The graphene quantum dot (GQD) is made of electrically gated stripe with zigzag edges. Inside the active region (AR), which is enclosed between the source and drain electrodes, there are two sharp energy ($pm $)-levels, whose separation $2Delta $ is controlled with Stark effect by applying the lateral dc electric field. Such the edge states determine the unique nature of elementary excitations, chiral fermions, that are responsible for the non-linear optical responce revealing a potential for many applications. They are, e.g., the frequency multiplication and self-focusing of two dimensional solitons. Furthemore, when injection of the non-equilibrium electrons causes an inverse population of the levels localized in AR, the subsequent recombination of electrons and holes leads to a coherent emission of the THz waves.

Published : "arXiv Mesoscale and Nanoscale Physics".

Optimal transport and colossal ionic mechano–conductance in graphene crown ethers. (arXiv:1907.07683v1 [cond-mat.mes-hall])

2019-07-19T04:34:30+00:00July 19th, 2019|Categories: Publications|Tags: |

Biological ion channels balance electrostatic and dehydration effects to yield large ion selectivities alongside high transport rates. These macromolecular systems are often interrogated through point mutations of their pore domain, limiting the scope of mechanistic studies. In contrast, we demonstrate that graphene crown ether pores afford a simple platform to directly investigate optimal ion transport conditions, i.e., maximum current densities and selectivity. Crown ethers are known for selective ion adsorption. When embedded in graphene, however, transport rates lie below the drift-diffusion limit. We show that small pore strains — 1 % — give rise to a colossal — 100 % — change in conductance. This process is electromechanically tunable, with optimal transport in a primarily diffusive regime, tending toward barrierless transport, as opposed to a knock-on mechanism. Measurements of mechanical current modulation will yield direct information on the local electrostatic conditions of the pore. These observations suggest a novel setup for nanofluidic devices while giving insight into the physical foundation of evolutionarily–optimized ion transport in biological pores.

Published : "arXiv Mesoscale and Nanoscale Physics".

High-performance monolayer MoS2 field-effect transistor with large-scale nitrogen-doped graphene electrodes for Ohmic contact. (arXiv:1907.07883v1 [cond-mat.mtrl-sci])

2019-07-19T02:33:22+00:00July 19th, 2019|Categories: Publications|Tags: , |

A finite Schottky barrier and large contact resistance between monolayer MoS2 and electrodes are the major bottlenecks in developing high-performance field-effect transistors (FETs) that hinder the study of intrinsic quantum behaviors such as valley-spin transport at low temperature. A gate-tunable graphene electrode platform has been developed to improve the performance of MoS2 FETs. However, intrinsic misalignment between the work function of pristine graphene and the conduction band of MoS2 results in a large threshold voltage for the FETs, because of which Ohmic contact behaviors are observed only at very high gate voltages and carrier concentrations (~1013 cm-2). Here, we present high-performance monolayer MoS2 FETs with Ohmic contact at a modest gate voltage by using a chemical-vapor-deposited (CVD) nitrogen-doped graphene with a high intrinsic electron carrier density. The CVD nitrogen-doped graphene and monolayer MoS2 hybrid FETs platform exhibited a large negative shifted threshold voltage of -54.2 V and barrier-free Ohmic contact under zero gate voltage. Transparent contact by nitrogen-doped graphene led to a 214% enhancement in the on-current and a four-fold improvement in the field-effect carrier mobility of monolayer MoS2 FETs compared with those of a pristine graphene electrode platform. The transport measurements, as well as Raman and X-ray photoelectron spectroscopy analyses before and after thermal annealing, reveal that the atomic C-N bonding in the CVD nitrogen-doped graphene is responsible for the dominant effects of electron doping. Large-scale nitrogen-doped graphene electrodes provide a promising device platform for the development of high-performance devices and the study of unique quantum behaviors.

Published in: "arXiv Material Science".

Ultrafast lithium diffusion in bilayer buckled graphene: A comparative study of Li and Na. (arXiv:1907.07988v1 [cond-mat.mtrl-sci])

2019-07-19T02:33:19+00:00July 19th, 2019|Categories: Publications|Tags: |

The effect of the curvature of bilayer graphene on the interlayer diffusion of Li atoms is investigated using molecular dynamics simulations. A spectacular enhancement of the diffusion constant parallel to the folding axis is found. The ratio of the parallel to the perpendicular diffusion depends on the buckling direction and stacking type, and it increases with the degree of buckling. The strongest anisotropy is observed in the case of fixed zig-zag edges. A comparison with the interlayer diffusion of Na suggests that the strong asymmetry in the vibrational states of buckled graphene and also the smaller mass of Li are likely to contribute to the observed diffusion enhancement. This work opens a new pathway to develop highly-efficient anodes for rechargeable alkaline batteries.

Published in: "arXiv Material Science".

Green Synthesis and Layer-by-Layer Assembly of Amino-Functionalized Graphene Oxide/Carboxylic Surface Modified Trimetallic Nanoparticles Nanocomposite for Label-Free Electrochemical Biosensing

2019-07-18T18:33:33+00:00July 18th, 2019|Categories: Publications|Tags: , |

In this context, a novel, scalable and facile method for the green synthesis of graphene oxide (GO) to facilitate effective and safe oxidation of graphite using sodium periodate (NaIO4) is demonstrated. The optimized value of the oxidizing agent NaIO4 ensured effective oxidation, minimized defects on sp2 C-C plane (ID/IG = 0.645) and increased C/O atomic ratio of ~5.146. Subsequently, we successfully synthesized the amino-functionalized reduced graphene oxide (NH2-rGO) and carboxylic surface modified AgPtPd (COOH-AgPtPd) trimetallic nanoparticles (TNPs), in order to fabricate a label-free electrochemical sensing platform using the conventional immersive layer-by-layer (LBL) assembly. The superior synergetic effect between LBL-assembled NH2-rGO and COOH-AgPtPd (COOH-AgPtPd/NH2-rGO) significantly boosts the electron transfer rate of the electrode as well as electrocatalytic efficiency. Therefore, the as-prepared COOH-AgPtPd/NH2-rGO nanocomposite-based sensing material was first employed for nonenzymatic electrochemical detection of H2O2, with a low detection limit of 0.2 nM. Moreover, COOH-AgPtPd/NH2-rGO nanocomposite can also be utilized as a sensing platform for label-free accurate electrochemical detection of prostate-specific antigen (PSA) over a large linear range of 4 fg mL–1 to 300 ng mL–1, with an ultra-low detection limit (LOD) of 4 fg mL–1.

Published in: "Journal of the Electrochemical Society".

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