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Boundary activated hydrogen evolution reaction on monolayer MoS<sub>2</sub>

2019-03-22T18:35:08+00:00March 22nd, 2019|Categories: Publications|Tags: , |

Boundary activated hydrogen evolution reaction on monolayer MoS2Boundary activated hydrogen evolution reaction on monolayer MoS<sub>2</sub>, Published online: 22 March 2019; doi:10.1038/s41467-019-09269-9While water-splitting electrocatalysts enable energy storage in carbon-neutral fuels, a recent challenge has been the discovery and understanding of catalyst active sites. Here, authors find domain boundaries in MoS2 materials to present high-activity, stable, and scalable sites for H2 evolution.

Published in: "Nature Communications".

Nonlocal quantum gain facilitates loss compensation and plasmon amplification in graphene hyperbolic metamaterials

2019-03-22T18:34:25+00:00March 22nd, 2019|Categories: Publications|Tags: |

Author(s): Illya I. Tarasenko, A. Freddie Page, Joachim M. Hamm, and Ortwin HessGraphene-based hyperbolic metamaterials have been predicted to transport evanescent fields with extraordinarily large vacuum wave vectors. It is particularly at much higher wave vector values that the commonly employed descriptional models involving structure homogenization and assumptions of an app…[Phys. Rev. B 99, 115430] Published Fri Mar 22, 2019

Published in: "Physical Review B".

Antibody-modified reduced graphene oxide film for circulating tumor cell detection in early-stage prostate cancer patients

2019-03-22T16:34:27+00:00March 22nd, 2019|Categories: Publications|Tags: , |

RSC Adv., 2019, 9,9379-9385DOI: 10.1039/C8RA08682F, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Binshuai Wang, Yimeng Song, Liyuan Ge, Shudong Zhang, Lulin MaWe report the fabrication of an antibody-modified reduced graphene oxide film, which can be

Published in: "RSC Advances".

1D metallic edge states of oxygen-terminated zigzag graphene edges

2019-03-22T15:03:20+00:00March 22nd, 2019|Categories: Publications|Tags: |

The honeycomb lattice of graphene exhibits a chiral symmetry that guarantees a Dirac point where linearly dispersing bands crosses with zero density of states. Enhanced functionalities such as metallicity and semi-conductivity are predicted by breaking the chiral symmetry in graphene zigzag nanoribbons and the selective chemical functionalization of their edges. Here we synthesize oxygen-terminated zigzag ribbons via Ag catalytic nanoparticle-assisted oxygen etching of epitaxial graphene/SiC(0 0 0 1). Using scanning tunneling microscopy/spectroscopy and density functional calculations, we demonstrate 1D metallic edges in oxygen terminated zigzag edges, due to two sets of states at the Dirac point—localized oxygen-induced states and extended resonances derived from the Dirac states of graphene. The edges states are robust, persisting even after air exposure. These findings indicate that the selective functionalization of graphene edges can be an effective means to tailor its prop…

Published in: "2DMaterials".

Semiconductor channel-mediated photodoping in h-BN encapsulated monolayer MoSe 2 phototransistors

2019-03-22T15:03:18+00:00March 22nd, 2019|Categories: Publications|Tags: , |

In optically excited 2D phototransistors, charge transport is often affected by photodoping effects. Recently, it was shown that such effects are especially strong and persistent for graphene/h-BN heterostructures, and that they can be used to controllably tune the charge neutrality point of graphene. In this work we investigate how this technique can be extended to h-BN encapsulated monolayer MoSe 2 phototransistors at room temperature. By exposing the sample to 785 nm laser excitation we can controllably increase the charge carrier density of the MoSe 2 channel by Δ n   ≈  4.45  ×  10 12 cm −2 , equivalent to applying a back gate voltage of ~60 V. We also evaluate the efficiency of photodoping at different illumination wavelengths, finding that it is strongly correlated with the light absorption by the MoSe 2 layer, and maximizes for excitation on-resonance with the A exciton absorption. This indicates that the photodoping …

Published in: "2DMaterials".

Spin relaxation in fluorinated single and bilayer graphene. (arXiv:1903.08973v1 [cond-mat.mes-hall])

2019-03-22T04:30:30+00:00March 22nd, 2019|Categories: Publications|Tags: |

We present a joint experiment-theory study on the role of fluorine adatoms in spin and momentum scattering of charge carriers in dilute fluorinated graphene and bilayer graphene. The experimental spin-flip and momentum scattering rates and their dependence on the density of fluorine and carrier doping are obtained through weak localization and conductivity measurements, respectively, and suggest the role of fluorine as resonant magnetic impurities. For the estimated fluorine concentration of a few 100 ppm, the observed spin lifetimes are in the range of 1-10,ps. Theoretically, we established tight-binding electronic structures of fluorinated graphene and bilayer graphene by fitting to density functional supercell calculations and performed a comprehensive analysis of the spin-flip and momentum scattering rates within the same devices, aiming to develop a consistent description of both scattering channels. We find that resonant scattering in graphene is very sensitive to the precise position of the resonance level, as well as to the magnitude of the exchange coupling between itinerant carriers and localized spins. The experimental data point to the presence of weak spin-flip scatterers that, at the same time, relax the electron momentum strongly, nearly preserving the electron-hole symmetry. Such scatterers would exhibit resonance energies much closer to the neutrality point than what density functional theory predicts in the dilute limit. The inclusion of a magnetic moment on fluorine adatoms allowed us to qualitatively capture the carrier density dependence of the experimental rates but predicts a greater (weaker) spin (momentum) relaxation rate than the measurements. We discuss possible scenarios that

Published : "arXiv Mesoscale and Nanoscale Physics".

Direct observation of a flat band and a partially filled interlayer band in a Cs/graphene/Cs trilayer. (arXiv:1903.09038v1 [cond-mat.mes-hall])

2019-03-22T04:30:26+00:00March 22nd, 2019|Categories: Publications|Tags: , |

We investigate, using angle-resolved photoemission spectroscopy (ARPES), the electronic structure of graphene sandwiched in between two Cs layers with $2times 2$ and $sqrt{3}timessqrt{3}$ structures. ARPES reveals that this trilayer has a flat electron energy dispersion at the Fermi level and a partially occupied alkali metal $s$ band. The joint occurence of these two features together has proven impossible to achieve so far. Here, we introduce a technique to induce these features by the backfolding of graphene bands in a $2times 2$ superstructure and their subsequent hybridization with Cs derived states. The large band renormalization reduces the $pi$ to $pi^*$ transition energy at the $M$ point to only $4.15$~eV. Hence the excitations of this system can be probed by optical methods with ultraviolet (UV) excitation energy. Performing UV, ultra-high vacuum Raman spectroscopy of this trilayer, we find the Raman $G$ band of graphene is shifted down in frequency by almost 60~cm$^{-1}$ and sharply reduces its Fano asymmetry as the Fermi level is pushed beyond the Lifshitz transition.

Published : "arXiv Mesoscale and Nanoscale Physics".

Large enhancement of conductivity in Weyl semimetals with tilted cones: pseudo-relativity and linear response. (arXiv:1903.09081v1 [cond-mat.mes-hall])

2019-03-22T04:30:22+00:00March 22nd, 2019|Categories: Publications|Tags: |

We study the conductivity of two-dimensional graphene-type materials with tilted cones as well as their three-dimensional Weyl counterparts and show that a covariant quantum Boltzmann equation is capable of providing an accurate description of these materials’ transport properties. The validity of the covariant Boltzmann approach is corroborated by calculations within the Kubo formula. We find a strong anisotropy in the conductivities parallel and perpendicular to the tilt direction upon increase of the tilt parameter $eta$, which can be interpreted as the boost parameter of a Lorentz transformation. While the ratio between the two conductivities is $sqrt{1-eta^2}$ in the two-dimensional case where only the conductivity perpendicular to the tilt direction diverges for $etarightarrow 1$, both conductivities diverge in three-dimensional Weyl semimetals, where $eta=1$ separates a type-I (for $eta<1$) from a type-II Weyl semimetal (for $eta>1$).

Published : "arXiv Mesoscale and Nanoscale Physics".

Liquid-phase exfoliated indium-selenide flakes and their application in hydrogen evolution reaction. (arXiv:1903.08967v1 [cond-mat.mtrl-sci])

2019-03-22T02:29:27+00:00March 22nd, 2019|Categories: Publications|Tags: , , |

Single- and few-layered InSe flakes are produced by the liquid-phase exfoliation of beta-InSe single crystals in 2-propanol, obtaining stable dispersions with a concentration as high as 0.11 g/L. Ultracentrifugation is used to tune the morphology, i.e., the lateral size and thickness of the as-produced InSe flakes. We demonstrate that the obtained InSe flakes have maximum lateral sizes ranging from 30 nm to a few um, and thicknesses ranging from 1 to 20 nm, with a max population centred at ~ 5 nm, corresponding to 4 Se-In-In-Se quaternary layers. We also show that no formation of further InSe-based compounds (such as In2Se3) or oxides occurs during the exfoliation process. The potential of these exfoliated-InSe few-layer flakes as a catalyst for hydrogen evolution reaction (HER) is tested in hybrid single-walled carbon nanotubes/InSe heterostructures. We highlight the dependence of the InSe flakes morphologies, i.e., surface area and thickness, on the HER performances achieving best efficiencies with small flakes offering predominant edge effects. Our theoretical model unveils the origin of the catalytic efficiency of InSe flakes, and correlates the catalytic activity to the Se vacancies at the edge of the flakes.

Published in: "arXiv Material Science".

WS2-graphite dual-ion battery. (arXiv:1903.08961v1 [cond-mat.mtrl-sci])

2019-03-22T02:29:24+00:00March 22nd, 2019|Categories: Publications|Tags: , |

A novel WS2-graphite dual-ion battery (DIB) is developed by combining together a conventional graphite cathode and high-capacity few-layer WS2 flakes anode. The WS2 flakes are produced by exploiting wet-jet milling (WJM) exfoliation, which allows mass production of few-layer WS2 flakes in dispersion, with an exfoliation yield of 100%. The WS2-anodes enable DIBs, based on hexafluorophosphate (PF6-) and lithium (Li+) ions, to achieve charge specific capacities of 457, 438, 421, 403, 295 and 169 mAh g-1 at current rates of 0.1, 0.2, 0.3, 0.4, 0.8 and 1.0 A g-1, respectively, outperforming conventional DIBs. The WS2-based DIBs operate in the 0 to 4 V cell voltage range, thus extending the operating voltage window of conventional WS2-based Li-ion batteries (LIBs). These results demonstrate a new route towards the exploitation of WS2, and possibly other transition metal dichalcogenides (TMDs), for the development of next-generation energy storage devices.

Published in: "arXiv Material Science".

Engineered MoSe2-based heterostructures for efficient electrochemical hydrogen evolution reaction. (arXiv:1903.08951v1 [cond-mat.mtrl-sci])

2019-03-22T02:29:22+00:00March 22nd, 2019|Categories: Publications|Tags: , , |

Two-dimensional transition metal-dichalcogenides are emerging as efficient and cost-effective electrocatalysts for hydrogen evolution reaction (HER). However, only the edge sites of their trigonal prismatic phase show HER-electrocatalytic properties, while the basal plane, which is absent of defective/unsaturated sites, is inactive. Here, we tackle the key challenge that is increasing the number of electrocatalytic sites by designing and engineering heterostructures composed of single-/few-layer MoSe2 flakes and carbon nanomaterials (graphene or single-wall carbon nanotubes (SWNTs)) produced by solution processing. The electrochemical coupling between the materials that comprise the heterostructure effectively enhances the HER-electrocatalytic activity of the native MoSe2 flakes. The optimization of the mass loading of MoSe2 flakes and their electrode assembly via monolithic heterostructure stacking provided a cathodic current density of 10mAcm-2 at overpotential of 100mV, a Tafel slope of 63mVdec-1 and an exchange current density (j0) of 0.203 Acm-2. In addition, electrode thermal annealing in a hydrogen environment and chemical bathing in n-butyllithium are exploited to texturize the basal planes of the MoSe2 flakes (through Se-vacancies creation) and to achieve in situ semiconducting-to-metallic phase conversion, respectively, thus they activate new HER-electrocatalytic sites. The as-engineered electrodes show a 4.8-fold enhancement of j0 and a decrease in the Tafel slope to 54mVdec-1.

Published in: "arXiv Material Science".

Doped-MoSe2 nanoflakes/3d metal oxide-hydr(oxy)oxides hybrid catalysts for pH-universal electrochemical hydrogen evolution reaction. (arXiv:1903.08947v1 [cond-mat.mtrl-sci])

2019-03-22T02:29:20+00:00March 22nd, 2019|Categories: Publications|Tags: , , |

Clean hydrogen production through efficient and cost-effective electrochemical water splitting is highly promising to meeting future global energy demands. The design of Earth-abundant materials with both high activity for hydrogen evolution reaction (HER) and electrochemical stability in both acidic and alkaline environments summarize the outcomes needed for practical applications. Here, we report a non-noble 3d metal Cl-chemical doping of liquid phase exfoliated single/few-layer flakes of MoSe2 for creating MoSe2 nanoflakes/3d metal oxide-hydr(oxy)oxide hybrid HER-catalysts. We propose that the electron-transfer from MoSe2 nanoflakes to metal cations and the chlorine complexation-induced both neutralization, as well as the in situ formation of metal oxide-hydr(oxy)oxides on MoSe2 nanoflake’s surface, tailor the proton affinity of the derived catalysts, increasing the number and HER-kinetic of their active sites in both acidic and alkaline electrolytes. The electrochemical coupling between the doped-MoSe2 nanoflakes/metal oxide-hydr(oxy)oxide hybrids and single-walled carbon nanotubes heterostructures further accelerates the HER process. Lastly, monolithic stacking of multiple heterostructures is reported as a facile electrode assembly strategy to achieve overpotential for a cathodic current density of 10mAcm-2 of 0.081V and 0.064V in 0.5M H2SO4 and 1M KOH, respectively. This opens up new opportunities to address the current density vs. overpotential requirements targeted in pH-universal H2 production.

Published in: "arXiv Material Science".

High thermal conductivity of high-quality monolayer boron nitride and its thermal expansion. (arXiv:1903.08862v1 [cond-mat.mtrl-sci])

2019-03-22T02:29:18+00:00March 22nd, 2019|Categories: Publications|Tags: , |

Heat management becomes more and more critical, especially in miniaturized modern devices, so the exploration of highly thermally conductive materials with electrical insulation and favorable mechanical properties is of great importance. Here, we report that high-quality monolayer boron nitride (BN) has a thermal conductivity (k{appa}) of 751 W/mK at room temperature. Though smaller than that of graphene, this value is larger than that of cubic boron nitride (cBN) and only second to those of diamond and lately discovered cubic boron arsenide (BAs). Monolayer BN has the second largest k{appa} per unit weight among all semiconductors and insulators, just behind diamond, if density is considered. The k{appa} of atomically thin BN decreases with increased thickness. Our large-scale molecular dynamic simulations using Green-Kubo formalism accurately reproduce this trend, and the density functional theory (DFT) calculations reveal the main scattering mechanism. The thermal expansion coefficients (TECs) of monolayer to trilayer BN at 300-400 K are also experimentally measured, and the results are comparable to atomistic ab initio DFT calculations in a wider range of temperatures. Thanks to its wide bandgap, high thermal conductivity, outstanding strength, good flexibility, and excellent thermal and chemical stability, atomically thin BN is a strong candidate for heat dissipation applications, especially in the next generation of flexible electronic devices.

Published in: "arXiv Material Science".

Yellow fluorescent graphene quantum dots as a phosphor for white tunable light-emitting diodes

2019-03-21T16:32:39+00:00March 21st, 2019|Categories: Publications|Tags: |

RSC Adv., 2019, 9,9301-9307DOI: 10.1039/C8RA10353D, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Luqiao Yin, Jipeng Zhou, Weitao Li, Jianhua Zhang, Liang WangTunable color temperature of graphene quantum dot-based white lighting emitting diodes had been achieved

Published in: "RSC Advances".

Boosting electrochemical oxygen reduction activity of hemoglobin onto [email protected] nanoplatforms

2019-03-21T14:34:41+00:00March 21st, 2019|Categories: Publications|Tags: |

Chem. Commun., 2019, Accepted ManuscriptDOI: 10.1039/C9CC01625B, CommunicationAna Franco, Manuel Cano, Juan José Giner-Casares, Enrique Rodriguez-Castellon, Rafael Luque, Alain Rafael Rafael Puente SantiagoA metal-free oxygen reduction reaction (ORR) electrocatalyst with oustanding performance was obtained through an easy and one-pot synthesis of hemoglobin functionalized [email protected] (GO) nanocomposites. The active pyridinic nitrogen sites of…The content of this RSS Feed (c) The Royal Society of Chemistry

Published in: "Chemical Communications".

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