Aggregation/dispersion-mediated peroxidase-like activity of MoS2 quantum dots for colorimetric pyrophosphate detection

2019-01-18T02:32:38+00:00January 18th, 2019|Categories: Publications|Tags: |

Chem. Commun., 2019, Accepted ManuscriptDOI: 10.1039/C8CC09799B, CommunicationWanqiang Xia, Pu Zhang, Wensheng Fu, Lianzhe Hu, Yi WangAs alternatives of natural enzymes, nanomaterials with enzyme-mimetic activity have received considerable attention due to their remarkable performances in chemical sensing. Although a variety of nano-enzymes have been reported, effective…The content of this RSS Feed (c) The Royal Society of Chemistry

Published in: "Chemical Communications".

Correlated optical and electron microscopy reveal the role of multiple defect species and local strain on quantum emission. (arXiv:1901.05952v1 [cond-mat.mtrl-sci])

2019-01-18T02:29:30+00:00January 18th, 2019|Categories: Publications|Tags: |

Color-centers in solids have emerged as promising candidates for quantum photonic computing, communications, and sensing applications. Defects in hexagonal boron nitride(hBN) possess high-brightness, room-temperature quantum emission, but their large spectral variability and unknown local structure significantly challenge their technological utility. Here, we directly correlate hBN quantum emission with its local, atomic-scale crystalline structure using correlated photoluminescence (PL) and cathodoluminescence (CL) spectroscopy. Across 20 emitters, we observe zero phonon lines (ZPLs) in PL and CL ranging from 540-720 nm. CL mapping reveals that multiple defects and distinct defect species located within an optically-diffraction-limited region can each contribute to the observed PL spectra. Through high resolution transmission electron imaging, we find that emitters are located in regions with multiple fork-like dislocations. Additionally, local strain maps indicate that strain is not responsible for observed ZPL spectral range, though it can enable spectral tuning of particular emitters. While many emitters have identical ZPLs in CL and PL, others exhibit reversible but distinct CL and PL peaks; density functional calculations indicate that defect complexes and charge-state transitions influence such emission spectra. Our results highlight the sensitivity of defect-driven quantum emission to the surrounding crystallography, providing a foundation for atomic-scale optical characterization.

Published in: "arXiv Material Science".

Damage-Free ALD Blocking Oxide Layer on Functionalized Graphene Nanosheets as Nonvolatile Memories

2019-01-18T00:34:52+00:00January 17th, 2019|Categories: Publications|Tags: |

In this brief, nonvolatile memory (NVM) devices, based on the capacitor structure with the graphene nanosheets (GNSs) as the discrete charge storage media and atomic-layer-deposited (ALD) Al2O3 dielectric as the blocking oxide (BO) layer, have been demonstrated. The GNSs are formed by using the gold (Au) nanoparticles as the self-aligned mask and functionalized by using the NH3 plasma to enrich the charge trapping centers. In addition, the ALD Al2O3 layer is adopted as the BO layer of the GNS NVMs, resulting in a damage-free deposition on GNSs, compared to the conventional chemical-vapor-deposited SiO2 layer. The GNS NVM devices with a 15-nm-thick ALD Al2O3 BO layer can exhibit an excellent endurance of more than 105 cycles and superior data retention of lower than 30% charge loss for 10 years, suitable for future NVM applications.

Published in: "IEEE Transactions on Electron Devices".

Charge transfer across monolayer/bilayer MoS 2 lateral interface and its influence on exciton and trion characteristics

2019-01-17T16:36:39+00:00January 17th, 2019|Categories: Publications|

The charge transfer phenomenon is identified to be a major factor determining exciton and trion characteristics of atomically thin MoS 2 layers in various stacking configurations. We report photoluminescence (PL) from CVD-grown layered MoS 2 in the presence of a skewed or a deformed triangular-shaped monolayer/bilayer (1L/2L) lateral interface. Integrated PL mapping images over the 1L and 2L MoS 2 regions revealed that the neutral exciton emission was significantly enhanced and exhibited an oscillatory behavior in its intensity in the 1L region near the 1L/2L boundary, whereas the negative trion emission remained unchanged. The interplays among the number of MoS 2 layers, a substrate, and a geometric boundary structure of the 1L/2L lateral interface turned out to be important in charge transfer due to a modulation in work functions. Density functional theory predicted that the work functions of 1L and 2L MoS 2 were strongly influ…

Published in: "2DMaterials".

A roadmap for electronic grade 2D materials

2019-01-17T16:36:36+00:00January 17th, 2019|Categories: Publications|Tags: |

Since their modern debut in 2004, 2-dimensional (2D) materials continue to exhibit scientific and industrial promise, providing a broad materials platform for scientific investigation, and development of nano- and atomic-scale devices. A significant focus of the last decade’s research in this field has been 2D semiconductors, whose electronic properties can be tuned through manipulation of dimensionality, substrate engineering, strain, and doping (Mak et al 2010 Phys. Rev. Lett . 105 136805; Zhang et al 2017 Sci. Rep . 7 16938; Conley et al 2013 Nano Lett . 13 3626–30; Li et al 2016 Adv. Mater . 28 8240–7; Rhodes et al 2017 Nano Lett . 17 1616–22; Gong et al 2014 Nano Lett . 14 442–9; Suh et al 2014 Nano Lett . 14 6976–82; Yoshida et al 2015 Sci. Rep . 5 14808). Molybdenum disulfide (MoS 2 ) and tungsten diseleni…

Published in: "2DMaterials".

WSe 2 homojunctions and quantum dots created by patterned hydrogenation of epitaxial graphene substrates

2019-01-17T16:36:34+00:00January 17th, 2019|Categories: Publications|Tags: |

Scanning tunneling microscopy (STM) at 5 K is used to study WSe 2 layers grown on epitaxial graphene which is formed on Si-terminated SiC(0 0 0 1). Specifically, a partial hydrogenation process is applied to intercalate hydrogen at the SiC–graphene interface, yielding areas of quasi-free-standing bilayer graphene coexisting with bare monolayer graphene. We find that an abrupt and structurally perfect homojunction (band-edge offset ~0.25 eV) is formed when WSe 2 overgrows a lateral junction between adjacent monolayer and quasi-free-standing bilayer areas in the graphene. The band structure modulation in the WSe 2 overlayer arises from the varying work function (electrostatic potential) of the graphene beneath. Scanning tunneling spectroscopy measurements reveal that this effect can be also utilized to create WSe 2 quantum dots that confine either valence or conduction band states, in agreement with first-principles band structure calculatio…

Published in: "2DMaterials".

Influence of the head group on dynamics in surfactant intercalated graphite oxide

2019-01-17T16:34:47+00:00January 17th, 2019|Categories: Publications|

RSC Adv., 2019, 9,2277-2283DOI: 10.1039/C8RA08652D, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Xiaoqian Ai, Minmin Zhang, Ye Yan, Xiaoming Zhang, Xiaoxiao Cao, Qiong Wang, Ligang MaThe influence of the headgroup on the dynamics of three

Published in: "RSC Advances".

Pressure-induced magnetism in rotated graphene bilayers

2019-01-17T14:46:49+00:00January 17th, 2019|Categories: Publications|Tags: |

Author(s): Felix YndurainUsing ab initio methods based on density functional theory, we show that rotated graphene bilayers at angles different from the magic ones can have an electronic spectrum similar to those by applying moderate external pressures. We find that for an angle of 5.08∘ and a pressure of 2.19 GPa, the spin…[Phys. Rev. B 99, 045423] Published Thu Jan 17, 2019

Published in: "Physical Review B".

Strain Engineering of 2D Materials: Issues and Opportunities at the Interface

2019-01-17T10:48:21+00:00January 17th, 2019|Categories: Publications|

The strain engineering of 2D materials is particularly exciting, because an individual sheet can survive remarkably large mechanical strain and its atomic thinness allows mechanical deformations like a piece of paper. These exceptional circumstances create opportunities for the study of new fundamental physics and applications of 2D materials emerging at the large strain level. Abstract Triggered by the growing needs of developing semiconductor devices at ever‐decreasing scales, strain engineering of 2D materials has recently seen a surge of interest. The goal of this principle is to exploit mechanical strain to tune the electronic and photonic performance of 2D materials and to ultimately achieve high‐performance 2D‐material‐based devices. Although strain engineering has been well studied for traditional semiconductor materials and is now routinely used in their manufacturing, recent experiments on strain engineering of 2D materials have shown new opportunities for fundamental physics and exciting applications, along with new challenges, due to the atomic nature of 2D materials. Here, recent advances in the application of mechanical strain into 2D materials are reviewed. These developments are categorized by the deformation modes of the 2D material–substrate system: in‐plane mode and out‐of‐plane mode. Recent state‐of‐the‐art characterization of the interface mechanics for these 2D material–substrate systems is also summarized. These advances highlight how the strain or strain‐coupled applications of 2D materials rely on the interfacial properties, essentially shear and adhesion, and finally offer direct guidelines for deterministic design of mechanical strains into 2D materials for ultrathin semiconductor applications.

Published in: "Advanced Materials".

Tailoring Lithium Deposition via an SEI‐Functionalized Membrane Derived from LiF Decorated Layered Carbon Structure

2019-01-17T08:34:15+00:00January 17th, 2019|Categories: Publications|Tags: , |

A surface conversion of LiF into C–F x components on a defective carbon sheet can be achieved during Li plating to provide a solid electrolyte interphase (SEI)‐functionalization of a layered carbon structure. Uniform Li deposition with dendrite‐free features can be realized beneath the SEI‐functionalized layer for significantly improved cycling stability of Li metal anodes. Abstract Lithium (Li) metal is a key anode material for constructing next generation high energy density batteries. However, dendritic Li deposition and unstable solid electrolyte interphase (SEI) layers still prevent practical application of Li metal anodes. In this work, it is demonstrated that an uniform Li coating can be achieved in a lithium fluoride (LiF) decorated layered structure of stacked graphene (SG), leading to the formation of an SEI‐functionalized membrane that retards electron transfer by three orders of magnitude to avoid undesirable Li deposition on the top surface, and ameliorates Li+ ion migration to enable uniform and dendrite‐free Li deposition beneath such an interlayer. Surface chemistry analysis and density functional theory calculations demonstrate that these beneficial features arise from the formation of C–F x surface components on the SG sheets during the Li coating process. Based on such an SEI‐functionalized membrane, stable cycling at high current densities up to 3 mA cm−2 and Li plating capacities up to 4 mAh cm−2 can be realized in LiPF6/carbonate electrolytes. This work elucidates the promising strategy of modifying Li plating behavior through the SEI‐functionalized carbon structure, with significantly improved cycling stability of rechargeable Li metal anodes.

Published in: "Advanced Energy Materials".

Electrocatalysts: Unsaturated Sulfur Edge Engineering of Strongly Coupled MoS2 Nanosheet–Carbon Macroporous Hybrid Catalyst for Enhanced Hydrogen Generation (Adv. Energy Mater. 2/2019)

2019-01-17T08:34:09+00:00January 17th, 2019|Categories: Publications|Tags: , |

In article number 1802553, Hao Jiang, Chunzhong Li and co‐workers develop a new strategy for making strongly coupled MoS2/C macroporous hybrid electrocatalysts with engineered unsaturated sulfur edges. The catalyst exhibits superior and stable catalytic activity toward HER in acidic and basic media.

Published in: "Advanced Energy Materials".

In Situ Synthesis of Hierarchical Core Double‐Shell Ti‐Doped [email protected](PO4)[email protected]/3D Graphene Cathode with High‐Rate Capability and Long Cycle Life for Lithium‐Ion Batteries

2019-01-17T08:34:01+00:00January 17th, 2019|Categories: Publications|Tags: , |

A hierarchical core double‐shell Ti‐doped [email protected](PO4)[email protected]/3D‐G architecture is smartly constructed via in situ synthetic methodology, and exhibits outstanding rate capability and superior cyclic stability for advanced lithium‐ion batteries as a competitive cathode, benefiting from synergetic contributions from the integrated design rationales. Abstract Olivine‐type LiMnPO4 (LMP) cathodes have gained enormous attraction for Li‐ion batteries (LIBs), thanks to their large theoretical capacity, high discharge platform, and thermal stability. However, it is still hugely challenging to achieve encouraging Li‐storage behaviors owing to their low electronic conductivity and limited lithium diffusion. Herein, the core double‐shell Ti‐doped [email protected](PO4)[email protected]/3D graphene ([email protected]@C/3D‐G) architecture is designed and constructed via an in situ synthetic methodology. A continuous electronic conducting network is formed with the unfolded 3D‐G and conducting carbon nanoshell. The Nasicon‐type NTP nanoshell with exceptional ionic conductivity efficiently inhibits gradual enrichment in by‐products, and renders low surfacial/interfacial electron/ion‐diffusion resistance. Besides, a rapid Li+ diffusion in the bulk structure is guaranteed with the reduction of MnLi+˙ antisite defects originating from the synchronous Ti‐doping. Benefiting from synergetic contributions from these design rationales, the integrated [email protected]@C/3D‐G cathode yields high initial discharge capacity of ≈164.8 mAh g−1 at 0.05 C, high‐rate reversible capacity of ≈116.2 mAh g−1 at 10 C, and long‐term capacity retention of ≈93.3% after 600 cycles at 2 C. More significantly, the electrode design developed here will exert significant impact upon constructing other advanced cathodes for high‐energy/power LIBs.

Published in: "Advanced Energy Materials".

Planar and van der Waals heterostructures for vertical tunnelling single electron transistors. (arXiv:1901.05211v1 [cond-mat.mes-hall])

2019-01-17T04:30:58+00:00January 17th, 2019|Categories: Publications|Tags: , , |

Despite a rich choice of two-dimensional materials, which exists these days, heterostructures, both vertical (van der Waals) and in-plane, offer an unprecedented control over the properties and functionalities of the resulted structures. Thus, planar heterostructures allow p-n junctions between different two-dimensional semiconductors and graphene nanoribbons with well-defined edges; and vertical heterostructures resulted in the observation of superconductivity in purely carbon-based systems and realisation of vertical tunnelling transistors. Here we demonstrate simultaneous use of in-plane and van der Waals heterostructures to build vertical single electron tunnelling transistors. We grow graphene quantum dots inside the matrix of hexagonal boron nitride, which allows a dramatic reduction of the number of localised states along the perimeter of the quantum dots. The use of hexagonal boron nitride tunnel barriers as contacts to the graphene quantum dots make our transistors reproducible and not dependent on the localised states, opening even larger flexibility when designing future devices.

Published : "arXiv Mesoscale and Nanoscale Physics".

Van Hove Singularities and Excited-State Quantum Phase Transitions in Graphene-like Microwave Billiards. (arXiv:1901.05319v1 [cond-mat.mes-hall])

2019-01-17T04:30:50+00:00January 17th, 2019|Categories: Publications|Tags: |

We discuss solutions of an algebraic model of the hexagonal lattice vibrations, which point out interesting localization properties of the eigenstates at van Hove singularities (vHs), whose energies correspond to Excited-State Quantum Phase Transitions (ESQPT). We show that these states form stripes oriented parallel to the zig-zag direction of the lattice, similar to the well-known edge states found at the Dirac point, however the vHs-stripes appear in the bulk. We interpret the states as lines of cell-tilting vibrations, and inspect their stability in the large lattice-size limit. The model can be experimentally realized by superconducting 2D microwave resonators containing triangular lattices of metallic cylinders, which simulate finite-sized graphene flakes. Thus we can assume that the effects discussed here could be experimentally observed.

Published : "arXiv Mesoscale and Nanoscale Physics".

Breakdown of the Wiedemann-Franz law in AB-stacked bilayer graphene. (arXiv:1901.05077v1 [cond-mat.mes-hall])

2019-01-17T04:30:45+00:00January 17th, 2019|Categories: Publications|Tags: |

We present a simple theory of thermoelectric transport in bilayer graphene and report our results for the electrical resistivity, the thermal resistivity, the Seebeck coefficient, and the Wiedemann-Franz ratio as functions of doping density and temperature. In the absence of disorder, the thermal resistivity tends to zero as the charge neutrality point is approached; the electric resistivity jumps from zero to an intrinsic finite value, and the Seebeck coefficient diverges in the same limit. Even though these results are similar to those obtained for single-layer graphene, their derivation is considerably more delicate. The singularities are removed by the inclusion of a small amount of disorder, which leads to the appearance of a “window” of doping densities $0<n<n_c$ (with $n_c$ tending to zero in the zero-disorder limit) in which the Wiedemann-Franz law is severely violated.

Published : "arXiv Mesoscale and Nanoscale Physics".

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