Ju Li

Xi'an Jiaotong University, Ch’ang-an, Shaanxi, China

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Publications (245)1703.44 Total impact

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    ABSTRACT: Silica (SiO2) glass, an essential material in human civilization, possesses excellent formability near its glass-transition temperature (Tg > 1100°C). However, bulk SiO2 glass is very brittle at room temperature. Here we show a surprising brittle-to-ductile transition of SiO2 glass nanofibers at room temperature as its diameter reduces below 18 nm, accompanied by ultrahigh fracture strength. Large tensile plastic elongation up to 18% can be achieved at low strain rate. The unexpected ductility is due to a free surface affected zone in the nanofibers, with enhanced ionic mobility compared to the bulk that improves ductility by producing more bond-switching events per irreversible bond loss under tensile stress. Our discovery is fundamentally important for understanding the damage tolerance of small-scale amorphous structures.
    Nano Letters 11/2015; DOI:10.1021/acs.nanolett.5b03070 · 13.59 Impact Factor
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    ABSTRACT: Liquid-cell in-situ transmission electron microscopy (TEM) observations of the charge/discharge reactions of non-aqueous Li-oxygen battery cathode were performed with ~5nm spatial resolution. The discharging reaction occurred at the interface between the electrolyte and the reaction product, while in charging the reactant was decomposed at the contact with the gold current collector, indicating that the lithium ion diffusivity / electronic conductivity is the limiting factor in discharging / charging, respectively, which is a root cause for the asymmetry in discharging / charging overpotential. Detachments of lithium oxide particles from the current collector into the liquid electrolyte are frequently seen when the cell was discharged at high overpotentials, with loss of active materials into liquid electrolyte ("flotsam") under minute liquid flow agitation, as the lithium peroxide dendritic trees are shown to be fragile mechanically and electrically. Our result implies that enhancing the binding force between the reaction products and the current collector to maintain robust electronic conduction is a key for improving the battery performance. This work demonstrated for the first time the in-situ TEM observation of a three-phase-reaction involving gold electrode, DMSO electrolyte and lithium salt, and O</sub>2</sub> gas. The technique described in this work is not limited to Li-oxygen battery, but can also be potentially used in other applications involving gas/liquid/solid electrochemical reactions.
    Nano Letters 11/2015; DOI:10.1021/acs.nanolett.5b03812 · 13.59 Impact Factor
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    ABSTRACT: Great efforts have been made to synthesize ZnO nanowires (NWs) as building blocks for a broad range of applications because of their unique mechanical and mechanoelectrical properties. However, little attention has been paid to the correlation between the NWs synthesis condition and these properties. Here we demonstrate that by slightly adjusting the NW growth conditions, the cross-sectional shape of the NWs can be tuned from hexagonal to circular. Room temperature photoluminescence spectra suggested that NWs with cylindrical geometry have a higher density of point defects. In situ transmission electron microscopy (TEM) uniaxial tensile-electrical coupling tests revealed that for similar diameter, the Young's modulus and electrical resistivity of hexagonal NWs is always larger than that of cylindrical NWs while the piezoresistive coefficient of cylindrical NWs is generally higher. With decreasing diameter, the Young's modulus and the resistivity of NWs increase while their piezoresistive coefficient decreases, regardless of the sample geometry. Our findings shed new light on understanding and advancing the performance of ZnO NW based devices through optimizing the synthesis conditions of the NWs.
    Nano Letters 10/2015; DOI:10.1021/acs.nanolett.5b02852 · 13.59 Impact Factor
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    ABSTRACT: When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. Here we demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. This "cyclic healing" of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising from increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. These results point to a versatile pathway for controlled mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen.
    Proceedings of the National Academy of Sciences 10/2015; DOI:10.1073/pnas.1518200112 · 9.67 Impact Factor

  • Science China Technological Sciences 10/2015; DOI:10.1007/s11431-015-5935-8 · 1.19 Impact Factor
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    ABSTRACT: PbTe1-x Se x alloys are of special interest to thermoelectric applications. Inelastic x-ray scattering determination of phonon dispersion and lifetimes along the high symmetry directions for PbTe1-x Se x alloys are presented. By comparing with calculated results based on the virtual crystal model calculations combined with ab initio density functional theory, the validity of virtual crystal model is evaluated. The results indicate that the virtual crystal model is overall a good assumption for phonon frequencies and group velocities despite the softening of transverse acoustic phonon modes along [1 1 1] direction, while the treatment of lifetimes warrants caution. In addition, phonons remain a good description of vibrational modes in PbTe1-x Se x alloys.
    Journal of Physics Condensed Matter 09/2015; 27(37):375403. DOI:10.1088/0953-8984/27/37/375403 · 2.35 Impact Factor
  • Wei Guo · Zhao Wang · Ju Li ·
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    ABSTRACT: We predict a strongest size for the contact strength when asperity radii of curvature decrease below ten nanometers. The reason for such strongest size is found to be correlated with the competition between the dislocation plasticity and surface diffusional plasticity. The essential role of temperature is calculated and illustrated in a comprehensive asperity size-strength-temperature map taking into account the effect of contact velocity. Such map should be essential for various phenomena related to nanoscale contacts such as nanowire cold welding, self-assembly of nanoparticles and adhesive nano-pillar arrays, as well as the electrical, thermal and mechanical properties of macroscopic interfaces.
    Nano Letters 08/2015; 15(10). DOI:10.1021/acs.nanolett.5b02306 · 13.59 Impact Factor
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    ABSTRACT: Magnetic exchange driven proximity effect at a magnetic-insulator–topological-insulator (MI-TI) interface provides a rich playground for novel phenomena as well as a way to realize low energy dissipation quantum devices. Here we report a dramatic enhancement of proximity exchange coupling in the MI/magnetic-TI EuS/Sb[subscript 2-x]V[subscript x]Te[subscript 3] hybrid heterostructure, where V doping is used to drive the TI (Sb[subscript 2]Te[subscript 3]) magnetic. We observe an artificial antiferromagneticlike structure near the MI-TI interface, which may account for the enhanced proximity coupling. The interplay between the proximity effect and doping in a hybrid heterostructure provides insights into the engineering of magnetic ordering.
    Physical Review Letters 08/2015; 115(8). · 7.51 Impact Factor

  • 2D Materials 08/2015; 2(3):032003. DOI:10.1088/2053-1583/2/3/032003
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    ABSTRACT: Alloy-type anodes such as silicon and tin are gaining popularity in rechargeable Li-ion batteries, but their rate/cycling capabilities should be improved. Here by making yolk-shell nanocomposite of aluminium core (30 nm in diameter) and TiO2 shell (∼3 nm in thickness), with a tunable interspace, we achieve 10 C charge/discharge rate with reversible capacity exceeding 650 mAh g(-1) after 500 cycles, with a 3 mg cm(-2) loading. At 1 C, the capacity is approximately 1,200 mAh g(-1) after 500 cycles. Our one-pot synthesis route is simple and industrially scalable. This result may reverse the lagging status of aluminium among high-theoretical-capacity anodes.
    Nature Communications 08/2015; 6:7872. DOI:10.1038/ncomms8872 · 11.47 Impact Factor
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    ABSTRACT: Formation of low-resistance metal contacts is the biggest challenge that masks the intrinsic exceptional electronic properties of 2D WSe2 devices. We present the first comparative study of the interfacial properties between ML/BL WSe2 and Sc, Al, Ag, Au, Pd, and Pt contacts by using ab initio energy band calculations with inclusion of the spin-orbital coupling (SOC) effects and quantum transport simulations. The interlayer coupling tends to reduce both the electron and hole Schottky barrier heights (SBHs) and alters the polarity for WSe2-Au contact, while the SOC chiefly reduces the hole SBH. In the absence of the SOC, Pd contact has the smallest hole SBH with a value no less than 0.22 eV. Dramatically, Pt contact surpasses Pd contact and becomes p-type Ohmic or quasi-Ohmic contact with inclusion of the SOC. Our study provides a theoretical foundation for the selection of favorable metal electrodes in ML/BL WSe2 devices.
    Nanoscale 08/2015; DOI:10.1039/C5NR06204G · 7.39 Impact Factor
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    ABSTRACT: Using nanoscale electrical-discharge-induced rapid Joule heating, we developed a method for ultrafast shape change and joining of small-volume materials. Shape change is dominated by surface-tension-driven convection in the transient liquid melt, giving an extremely high strain rate of ~106 s–1. In addition, the heat can be dissipated in small volumes within a few microseconds through thermal conduction, quenching the melt back to the solid state with cooling rates up to 108 K·s-1. We demonstrate that this approach can be utilized for the ultrafast welding of small-volume crystalline Mo (a refractory metal) and amorphous Cu49Zr51 without introducing obvious microstructural changes, distinguishing the process from bulk welding. [Figure not available: see fulltext.] © 2015, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.
    Nano Research 07/2015; 8(7):2143-2151. DOI:10.1007/s12274-014-0685-7 · 7.01 Impact Factor
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    ABSTRACT: As-grown GaAs nanowires often possess high density of twin boundaries and stacking faults, which serve as scattering planes for electrons. Here, using density functional theory and Green’s function method, we demonstrate that the planar faults can significantly alter the transport properties depending on different planar defects and in-plane wavevector of the electronic state. Conductance eigenchannel analysis was applied to reveal the microscopic mechanism of electron scattering. A formalism is developed to estimate the reduction of the electron and hole mobilities due to planar faults and structural polytypes, based on quantum transmission coefficients computed in phase-coherent transport calculations. For twin spacing of 2.4 nm, electron mobility and hole mobility were predicted to be 3000 cm2/V/s and 500 cm2/V/s,respectively. The findings highlight the necessity of removing twins for high-performance nanowire solar cells.
    Computational Materials Science 07/2015; 108:258–263. DOI:10.1016/j.commatsci.2015.06.011 · 2.13 Impact Factor
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    ABSTRACT: Recently, phosphorene electronic and optoelectronic prototype devices have been fabricated with various metal electrodes. We systematically explore for the first time the contact properties of monolayer (ML) phosphorene with a series of commonly used metals (Al, Ag. Cu, Au, Cr, Ni, Ti, and Pd) via both ab initio electronic structure calculations and more reliable quantum transport simulations. Strong interactions are found between all the checked metals, with the energy band structure of ML phosphorene destroyed. In terms of the quantum transport simulations, ML phosphorene forms a n-type Schottky contact with Au, Cu, Cr, Al, and Ag electrodes, with electron Schottky barrier heights (SBHs) of 0.30, 0.34, 0.37, 0.51, and 0.52 eV, respectively, and p-type Schottky contact with Ti, Ni, and Pd electrodes, with hole SBHs of 0.30, 0.26, and 0.16 eV, respectively. These results are in good agreement with available experimental data. Our findings not only provide an insight into the ML phosphorene-metal interfaces but also help in ML phosphorene based device design.
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    ABSTRACT: The presence of excess hydrogen at the interface between a metal substrate and a protective oxide can cause blistering and spallation of the scale. However, it remains unclear how nanoscale bubbles manage to reach the critical size in the first place. Here, we perform in situ environmental transmission electron microscopy experiments of the aluminium metal/oxide interface under hydrogen exposure. It is found that once the interface is weakened by hydrogen segregation, surface diffusion of Al atoms initiates the formation of faceted cavities on the metal side, driven by Wulff reconstruction. The morphology and growth rate of these cavities are highly sensitive to the crystallographic orientation of the aluminium substrate. Once the cavities grow to a critical size, the internal gas pressure can become great enough to blister the oxide layer. Our findings have implications for understanding hydrogen damage of interfaces.
    Nature Material 06/2015; 14(9). DOI:10.1038/nmat4336 · 36.50 Impact Factor
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    ABSTRACT: The isolation of the two-dimensional semiconductor molybdenum disulphide introduced a new optically active material possessing a band gap that can be facilely tuned via elastic strain. As an atomically thin membrane with exceptional strength, monolayer molybdenum disulphide subjected to biaxial strain can embed wide band gap variations overlapping the visible light spectrum, with calculations showing the modified electronic potential emanating from point-induced tensile strain perturbations mimics the Coulomb potential in a mesoscopic atom. Here we realize and confirm this 'artificial atom' concept via capillary-pressure-induced nanoindentation of monolayer molybdenum disulphide from a tailored nanopattern, and demonstrate that a synthetic superlattice of these building blocks forms an optoelectronic crystal capable of broadband light absorption and efficient funnelling of photogenerated excitons to points of maximum strain at the artificial-atom nuclei. Such two-dimensional semiconductors with spatially textured band gaps represent a new class of materials, which may find applications in next-generation optoelectronics or photovoltaics.
    Nature Communications 06/2015; 6:7381. DOI:10.1038/ncomms8381 · 11.47 Impact Factor
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    ABSTRACT: By using multi-scale simulation techniques, we probed the role of hydrogen-vacancy complexes on nucleation and growth of proto nano-voids upon dislocation plasticity in α-Fe. Our atomistic simulations reveal that, unlike a lattice vacancy, a hydrogen-vacancy complex is not absorbed by dislocations sweeping through the lattice. Additionally, this complex has lower lattice diffusivity; therefore, it has a lower probability of encountering and being absorbed by various lattice sinks. Hence, it can exist metastably for a rather long time. Our large-scale atomistic simulations show that when metals undergo plastic deformation in the presence of hydrogen at low homologous temperatures, the mechanically driven out-of-equilibrium dislocation processes can produce extremely high concentrations of hydrogen-vacancy complex (10-5∼10-3). Under such high concentrations, these complexes prefer to grow by absorbing additional vacancies and act as the embryos for the formation of proto nano-voids. The current work provides the possible route for the experimentally observed nano-void formation in the context of hydrogen-induced failure and also bridge the link from the atomic-scale events to the macroscopic failure.
    International Journal of Plasticity 06/2015; 74. DOI:10.1016/j.ijplas.2015.05.017 · 5.57 Impact Factor
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    Yangyang Wang · Ruge Quhe · Dapeng Yu · Ju Li · Jing Lu ·
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    ABSTRACT: Spintronics involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. The fascinating spin-resolved properties of graphene motivate numerous researchers into the studies of spintronics in graphene and other two-dimensional (2D) materials. Silicene, silicon analog of graphene, is considered as a promising material for spintronics. Here, we present a review on the theoretical advances about the spin-dependent properties including the electric field and exchange field tunable topological properties of silicene and the corresponding spintronic device simulations.
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    ABSTRACT: At elevated temperatures, glasses crystallize via thermally activated diffusion. However, metallic glasses can also undergo deformation-induced crystallization at very low temperatures. Here we demonstrate the crystallization of Al50Fe50 metallic glasses under cyclic deformation at 50 K using molecular dynamics simulations and reveal the underlying atomic-scale processes. We demonstrate that stress-driven nonaffine atomic rearrangements, or shear diffusion transformation (SDT) events, lead to successive metabasin-to-metabasin transitions and long-range ordering. We also illustrate that the nucleation and growth of the crystal proceed via collective attachment of ordered clusters, advancing the amorphous/crystal interface in an intermittent manner. The cooperative nature of the steplike crystallization is attributed to the large activation volume of Eshelby transformations which generate as a by-product nonaffine diffusive atomic displacements that accumulate over loading cycles. The dual nature of shear (affine) and diffusion (nonaffine) in low-temperature stress-driven SDT events thus unifies inelasticity with crystallization.
    Physical Review B 06/2015; 91(21). DOI:10.1103/PhysRevB.91.214103 · 3.74 Impact Factor
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    ABSTRACT: Rejuvenation is the configurational excitation of amorphous materials and is one of the more promising approaches for improving the deformability of amorphous metals that usually exhibit macroscopic brittle fracture modes. Here, we propose a method to control the level of rejuvenation through systematic thermal processing and clarify the crucial feasibility conditions by means of molecular dynamics simulations of annealing and quenching. We also experimentally demonstrate rejuvenation level control in Zr 55 Al 10 Ni 5 Cu 30 bulk metallic glass. Our local heat-treatment recipe (rising temperature above 1.1T g , followed by a temperature quench rate exceeding the previous) opens avenue to modifying the glass properties after it has been cast and processed into near component shape, where a higher local cooling rate may be afforded by for example transient laser heating, adding spatial control and great flexibility to the processing.
    Scientific Reports 05/2015; 5. DOI:10.1038/srep10545 · 5.58 Impact Factor

Publication Stats

9k Citations
1,703.44 Total Impact Points


  • 2010-2015
    • Xi'an Jiaotong University
      • State Key Laboratory for Mechanical Behavior of Materials
      Ch’ang-an, Shaanxi, China
  • 1995-2015
    • Massachusetts Institute of Technology
      • • Department of Materials Science and Engineering
      • • Department of Nuclear Science and Engineering
      Cambridge, Massachusetts, United States
  • 2009-2012
    • William Penn University
      Filadelfia, Pennsylvania, United States
  • 2008-2011
    • University of Pennsylvania
      • Department of Materials Science and Engineering
      Philadelphia, PA, United States
    • Iowa State University
      • Department of Physics and Astronomy
      Ames, Iowa, United States
  • 2003-2008
    • The Ohio State University
      • Department of Materials Science and Engineering
      Columbus, Ohio, United States
  • 2001
    • Japan Atomic Energy Agency
      • Nuclear Science and Engineering Directorate
      Muramatsu, Niigata, Japan