Publications by authors named "Jiangwei Wang"

33 Publications

Revealing extreme twin-boundary shear deformability in metallic nanocrystals.

Sci Adv 2021 Sep 1;7(36):eabe4758. Epub 2021 Sep 1.

Center of Electron Microscopy and State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, P. R. China.

[Figure: see text].
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http://dx.doi.org/10.1126/sciadv.abe4758DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8442924PMC
September 2021

A molecular dynamics simulation on the atomic mass sensor made of monolayer diamond.

Nanotechnology 2021 Aug 31;32(47). Epub 2021 Aug 31.

College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao 266580, People's Republic of China.

The recently synthesized monolayer diamond-diamane has proved to possess excellent mechanical and electrical properties, and it holds great potential in the field of nano-mass sensors. Herein, a molecular dynamics (MD) simulation is employed to systematically investigate the vibration response of the diamane nanoribbon (DNR) for the mass inspection. The results show that under different attached masses, the natural frequency of DNR is about three times of that of the bilayer graphene nanoribbon (BGNR) with the same size. The edge flatness of the DNR can be maintained during the vibration process, while the edge of the BGNR will warp in the initial state. Increasing the pre-strain can significantly increase the natural frequency of the DNR, leading to a higher response sensitivity of the DNR. In addition, the DNR has a higher mass resolution than the BGNR, and can detect smaller attached mass. The position of the attached mass in the resonator has a significant effect on the detection response. When the attached mass is near the center of the resonator, the frequency shift reaches the maximum value, and then it rapidly decreases to zero when the attached mass is close to the edge of DNR. Finally, the attached mass has no obvious effect on the quality factor of the DNR, and its value is stable between 10and 10orders of magnitude. The theoretical results demonstrate the accuracy of the MD results. The MD simulations reveal that the DNR has important implications as a resonant material for nano-mass sensor in the future.
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http://dx.doi.org/10.1088/1361-6528/ac1d0aDOI Listing
August 2021

PCNA inhibition enhances the cytotoxicity of β-lapachone in NQO1-Positive cancer cells by augmentation of oxidative stress-induced DNA damage.

Cancer Lett 2021 Oct 27;519:304-314. Epub 2021 Jul 27.

Department of Radiation Oncology, Indiana University Melvin and Bren Simon Comprehensive Cancer Center, Indiana University School of Medicine, Indianapolis, IN, 46202, USA. Electronic address:

β-Lapachone is a classic quinone-containing antitumor NQO1-bioactivatable drug that directly kills NQO1-overexpressing cancer cells. However, the clinical applications of β-lapachone are primarily limited by its high toxicity and modest lethality. To overcome this side effect and expand the therapeutic utility of β-lapachone, we demonstrate the effects of a novel combination therapy including β-lapachone and the proliferating cell nuclear antigen (PCNA) inhibitor T2 amino alcohol (T2AA) on various NQO1 cancer cells. PCNA has DNA clamp processivity activity mediated by encircling double-stranded DNA to recruit proteins involved in DNA replication and DNA repair. In this study, we found that compared to monotherapy, a nontoxic dose of the T2AA synergized with a sublethal dose of β-lapachone in an NQO1-dependent manner and that combination therapy prevented DNA repair, increased double-strand break (DSB) formation and promoted programmed necrosis and G1 phase cell cycle arrest. We further determined that combination therapy enhanced antitumor efficacy and prolonged survival in Lewis lung carcinoma (LLC) xenografts model. Our findings show novel evidence for a new therapeutic approach that combines of β-lapachone treatment with PCNA inhibition that is highly effective in treating NQO1 solid tumor cells.
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http://dx.doi.org/10.1016/j.canlet.2021.07.040DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8403654PMC
October 2021

Defect-free potassium manganese hexacyanoferrate cathode material for high-performance potassium-ion batteries.

Nat Commun 2021 Apr 12;12(1):2167. Epub 2021 Apr 12.

School of Chemistry, Beihang University, Beijing, P. R. China.

Potassium-ion batteries (KIBs) are promising electrochemical energy storage systems because of their low cost and high energy density. However, practical exploitation of KIBs is hampered by the lack of high-performance cathode materials. Here we report a potassium manganese hexacyanoferrate (KMn[Fe(CN)]) material, with a negligible content of defects and water, for efficient high-voltage K-ion storage. When tested in combination with a K metal anode, the KMn[Fe(CN)]-based electrode enables a cell specific energy of 609.7 Wh kg and 80% capacity retention after 7800 cycles. Moreover, a K-ion full-cell consisting of graphite and KMn[Fe(CN)] as anode and cathode active materials, respectively, demonstrates a specific energy of 331.5 Wh kg, remarkable rate capability, and negligible capacity decay for 300 cycles. The remarkable electrochemical energy storage performances of the KMn[Fe(CN)] material are attributed to its stable frameworks that benefit from the defect-free structure.
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http://dx.doi.org/10.1038/s41467-021-22499-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8041879PMC
April 2021

Combined quantum tunnelling and dielectrophoretic trapping for molecular analysis at ultra-low analyte concentrations.

Nat Commun 2021 02 10;12(1):913. Epub 2021 Feb 10.

Department of Chemistry, Molecular Science Research Hub, Imperial College London, London, UK.

Quantum tunnelling offers a unique opportunity to study nanoscale objects with atomic resolution using electrical readout. However, practical implementation is impeded by the lack of simple, stable probes, that are required for successful operation. Existing platforms offer low throughput and operate in a limited range of analyte concentrations, as there is no active control to transport molecules to the sensor. We report on a standalone tunnelling probe based on double-barrelled capillary nanoelectrodes that do not require a conductive substrate to operate unlike other techniques, such as scanning tunnelling microscopy. These probes can be used to efficiently operate in solution environments and detect single molecules, including mononucleotides, oligonucleotides, and proteins. The probes are simple to fabricate, exhibit remarkable stability, and can be combined with dielectrophoretic trapping, enabling active analyte transport to the tunnelling sensor. The latter allows for up to 5-orders of magnitude increase in event detection rates and sub-femtomolar sensitivity.
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http://dx.doi.org/10.1038/s41467-021-21101-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7876030PMC
February 2021

Defect-driven selective metal oxidation at atomic scale.

Nat Commun 2021 Jan 25;12(1):558. Epub 2021 Jan 25.

Center of Electron Microscopy and State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027, China.

Nanoscale materials modified by crystal defects exhibit significantly different behaviours upon chemical reactions such as oxidation, catalysis, lithiation and epitaxial growth. However, unveiling the exact defect-controlled reaction dynamics (e.g. oxidation) at atomic scale remains a challenge for applications. Here, using in situ high-resolution transmission electron microscopy and first-principles calculations, we reveal the dynamics of a general site-selective oxidation behaviour in nanotwinned silver and palladium driven by individual stacking-faults and twin boundaries. The coherent planar defects crossing the surface exhibit the highest oxygen binding energies, leading to preferential nucleation of oxides at these intersections. Planar-fault mediated diffusion of oxygen atoms is shown to catalyse subsequent layer-by-layer inward oxide growth via atomic steps migrating on the oxide-metal interface. These findings provide an atomistic visualization of the complex reaction dynamics controlled by planar defects in metallic nanostructures, which could enable the modification of physiochemical performances in nanomaterials through defect engineering.
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http://dx.doi.org/10.1038/s41467-020-20876-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7835350PMC
January 2021

Double Ghost Convolution Attention Mechanism Network: A Framework for Hyperspectral Reconstruction of a Single RGB Image.

Sensors (Basel) 2021 Jan 19;21(2). Epub 2021 Jan 19.

College of Communication and Art Design, University of Shanghai for Science and Technology, Shanghai 200093, China.

Current research on the reconstruction of hyperspectral images from RGB images using deep learning mainly focuses on learning complex mappings through deeper and wider convolutional neural networks (CNNs). However, the reconstruction accuracy of the hyperspectral image is not high and among other issues the model for generating these images takes up too much storage space. In this study, we propose the double ghost convolution attention mechanism network (DGCAMN) framework for the reconstruction of a single RGB image to improve the accuracy of spectral reconstruction and reduce the storage occupied by the model. The proposed DGCAMN consists of a double ghost residual attention block (DGRAB) module and optimal nonlocal block (ONB). DGRAB module uses GhostNet and PRELU activation functions to reduce the calculation parameters of the data and reduce the storage size of the generative model. At the same time, the proposed double output feature Convolutional Block Attention Module (DOFCBAM) is used to capture the texture details on the feature map to maximize the content of the reconstructed hyperspectral image. In the proposed ONB, the Argmax activation function is used to obtain the region with the most abundant feature information and maximize the most useful feature parameters. This helps to improve the accuracy of spectral reconstruction. These contributions enable the DGCAMN framework to achieve the highest spectral accuracy with minimal storage consumption. The proposed method has been applied to the NTIRE 2020 dataset. Experimental results show that the proposed DGCAMN method outperforms the spectral accuracy reconstructed by advanced deep learning methods and greatly reduces storage consumption.
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http://dx.doi.org/10.3390/s21020666DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7835855PMC
January 2021

Free-Standing Two-Dimensional Gold Membranes Produced by Extreme Mechanical Thinning.

ACS Nano 2020 Nov 5. Epub 2020 Nov 5.

Center of Electron Microscopy and State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, P. R. China.

Two-dimensional (2D) materials exhibit exceptional physical and chemical properties owing to their atomically thin structures. However, it remains challenging to produce 2D materials consisting of pure monoelemental metallic atoms. Here free-standing 2D gold (Au) membranes were prepared transmission electron microscopy straining of Au films. The applied in-plane tensile strain induces an extensive amount of out-of-plane thinning deformation in a local region of an Au thin film, resulting in the nucleation and growth of a free-standing 2D Au membrane surrounded by its film matrix. This 2D membrane is shown to be one atom thick with a simple-hexagonal lattice, which forms an atomically sharp interface with the face-centered cubic lattice of the film matrix. Diffusive transport of surface atoms, in conjunction with the dynamic evolution of interface dislocations, plays important roles in the formation of 2D Au membranes during the mechanical thinning process. These results demonstrate a top-down approach to produce free-standing 2D membranes and provide a general understanding on extreme mechanical thinning of metallic films down to the single-atom-thick limit.
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http://dx.doi.org/10.1021/acsnano.0c06697DOI Listing
November 2020

Metallic nanocrystals with low angle grain boundary for controllable plastic reversibility.

Nat Commun 2020 Jun 18;11(1):3100. Epub 2020 Jun 18.

Center of Electron Microscopy and State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027, China.

Advanced nanodevices require reliable nanocomponents where mechanically-induced irreversible structural damage should be largely prevented. However, a practical methodology to improve the plastic reversibility of nanosized metals remains challenging. Here, we propose a grain boundary (GB) engineering protocol to realize controllable plastic reversibility in metallic nanocrystals. Both in situ nanomechanical testing and atomistic simulations demonstrate that custom-designed low-angle GBs with controlled misorientation can endow metallic bicrystals with endurable cyclic deformability via GB migration. Such fully reversible plasticity is predominantly governed by the conservative motion of Shockley partial dislocation pairs, which fundamentally suppress damage accumulation and preserve the structural stability. This reversible deformation is retained in a broad class of face-centred cubic metals with low stacking fault energies when tuning the GB structure, external geometry and loading conditions over a wide range. These findings shed light on practical advances in promoting cyclic deformability of metallic nanomaterials.
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http://dx.doi.org/10.1038/s41467-020-16869-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7303210PMC
June 2020

Anti-twinning in nanoscale tungsten.

Sci Adv 2020 Jun 3;6(23):eaay2792. Epub 2020 Jun 3.

Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.

Nanomaterials often surprise us with unexpected phenomena. Here, we report a discovery of the anti-twinning deformation, previously thought impossible, in nanoscale body-centered cubic (BCC) tungsten crystals. By conducting in situ transmission electron microscopy nanomechanical testing, we observed the nucleation and growth of anti-twins in tungsten nanowires with diameters less than about 20 nm. During anti-twinning, a shear displacement of 1/3〈111〉 occurs on every successive {112} plane, in contrast to an opposite shear displacement of by ordinary twinning. This asymmetry in the atomic-scale shear pathway leads to a much higher resistance to anti-twinning than ordinary twinning. However, anti-twinning can become active in nanosized BCC crystals under ultrahigh stresses, due to the limited number of plastic shear carriers in small crystal volumes. Our finding of the anti-twinning phenomenon has implications for harnessing unconventional deformation mechanisms to achieve high mechanical preformation by nanomaterials.
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http://dx.doi.org/10.1126/sciadv.aay2792DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7269652PMC
June 2020

Zoonotic Vectorborne Pathogens and Ectoparasites of Dogs and Cats in Eastern and Southeast Asia.

Emerg Infect Dis 2020 06;26(6):1221-1233

To provide data that can be used to inform treatment and prevention strategies for zoonotic pathogens in animal and human populations, we assessed the occurrence of zoonotic pathogens and their vectors on 2,381 client-owned dogs and cats living in metropolitan areas of 8 countries in eastern and Southeast Asia during 2017-2018. Overall exposure to ectoparasites was 42.4% in dogs and 31.3% in cats. Our data cover a wide geographic distribution of several pathogens, including Leishmania infantum and zoonotic species of filariae, and of animals infested with arthropods known to be vectors of zoonotic pathogens. Because dogs and cats share a common environment with humans, they are likely to be key reservoirs of pathogens that infect persons in the same environment. These results will help epidemiologists and policy makers provide tailored recommendations for future surveillance and prevention strategies.
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http://dx.doi.org/10.3201/eid2606.191832DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7258489PMC
June 2020

Unstable twin in body-centered cubic tungsten nanocrystals.

Nat Commun 2020 May 19;11(1):2497. Epub 2020 May 19.

Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, 15261, USA.

Twinning is commonly activated in plastic deformation of low stacking-fault face-centered cubic (Fcc) metals but rarely found in body-centered cubic (Bcc) metals under room temperature and slow strain rates. Here, by conducting in situ transmission electron microscopy (TEM) at atomic scale, we discover that, in stark contrast to those in most Fcc metals, a majority of deformation twins in Bcc metals are unstable and undergo spontaneously detwinning upon unloading. Such unexpected instability of Bcc twins is found to be closely related to the prevalence of the inclined twin boundaries-a peculiar structure where twin boundaries are not parallel to the twinning plane, and the degree of instability is in direct proportion to the fraction of the inclined twin boundary. This work provides significant insights into the structure and stability of deformation twins in Bcc metals.
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http://dx.doi.org/10.1038/s41467-020-16349-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7237484PMC
May 2020

The Interaction of Biofoulants and Calcareous Deposits on Corrosion Performance of Q235 in Seawater.

Materials (Basel) 2020 Feb 13;13(4). Epub 2020 Feb 13.

Key Laboratory of Marine Environmental Corrosion and Bio-Fouling, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266000, China.

An understanding of the interaction of calcareous deposits and biofoulants on the corrosion performance of steel during the fouling stage is both interesting and necessary. So, the effects of these factors on Q235 carbon steel were investigated and discussed for 20 weeks under real ocean conditions. The results indicate that calcareous deposits are favorable for the attachment of marine microorganisms. However, macroorganisms prefer adhering directly to the substrate. The generations of calcareous deposits have priority over the biofilm attachment under the condition of cathodic protection. Calcareous deposits can prevent steel against corrosion for four weeks without cathodic protection.
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http://dx.doi.org/10.3390/ma13040850DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7078610PMC
February 2020

Dual-Additive Assisted Chemical Vapor Deposition for the Growth of Mn-Doped 2D MoS with Tunable Electronic Properties.

Small 2020 Apr 2;16(15):e1903181. Epub 2019 Oct 2.

Shenzhen Geim Graphene Center, Tsinghua-Berkeley Shenzhen Institute, Tsinghua University, Shenzhen, Guangdong, 518055, P. R. China.

Doping of bulk silicon and III-V materials has paved the foundation of the current semiconductor industry. Controlled doping of 2D semiconductors, which can also be used to tune their bandgap and type of carrier thus changing their electronic, optical, and catalytic properties, remains challenging. Here the substitutional doping of nonlike element dopant (Mn) at the Mo sites of 2D MoS is reported to tune its electronic and catalytic properties. The key for the successful incorporation of Mn into the MoS lattice stems from the development of a new growth technology called dual-additive chemical vapor deposition. First, the addition of a MnO additive to the MoS growth process reshapes the morphology and increases lateral size of Mn-doped MoS . Second, a NaCl additive helps in promoting the substitutional doping and increases the concentration of Mn dopant to 1.7 at%. Because Mn has more valance electrons than Mo, its doping into MoS shifts the Fermi level toward the conduction band, resulting in improved electrical contact in field effect transistors. Mn doping also increases the hydrogen evolution activity of MoS electrocatalysts. This work provides a growth method for doping nonlike elements into 2D MoS and potentially many other 2D materials to modify their properties.
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http://dx.doi.org/10.1002/smll.201903181DOI Listing
April 2020

Size-dependent dislocation-twin interactions.

Nanoscale 2019 Jul 25;11(26):12672-12679. Epub 2019 Jun 25.

Department of Mechanical Engineering and Materials Science Program, The University of Vermont, Burlington, Vermont 05405, USA.

Dislocation-twin interactions critically control the plastic deformation and ultrahigh strength of nanotwinned metals. Here, we report a strong twin-thickness dependence of dislocation-twin interaction mechanisms from the tensile deformation of face-centered cubic metallic nanocrystals by in situ nanomechanical testing. Direct observations at atomic scale reveal that the predominant dislocation-twin interaction abruptly changes from dislocation transmission on the {111} slip planes to the unusual (100) slip plane of the twin, when the twin thickness is smaller than 4 layers. Using atomistic simulations, we find that the energy barrier for {100} slip transmission mechanism gradually decreases, with decreasing twin thickness, below the energy level required for normal (111) slip transmission, which remains identical for all twin sizes. Our in situ observations and simulations provide atomistic insights into a fundamentally new mechanism of plasticity in nanotwinned metals, down to the lowest twin size limit.
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http://dx.doi.org/10.1039/c9nr03637gDOI Listing
July 2019

Growth of environmentally stable transition metal selenide films.

Nat Mater 2019 06 11;18(6):602-607. Epub 2019 Mar 11.

National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China.

Two-dimensional transition metal selenides (TMSs) possess fascinating physical properties. However, many as-prepared TMSs are environmentally unstable and limited in sample size, which greatly hinder their wide applications in high-performance electrical devices. Here we develop a general two-step vapour deposition method and successfully grow different TMS films with controllable thickness, wafer size and high quality. The superconductivity of the grown NbSe film is comparable with sheets exfoliated from bulk materials, and can maintain stability after a variety of harsh treatments, which are ascribed to the absence of oxygen during the whole growth process. Such environmental stability can greatly simplify the fabrication procedure for device applications, and should be of both fundamental and technological significance in developing TMS-based devices.
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http://dx.doi.org/10.1038/s41563-019-0321-8DOI Listing
June 2019

In situ atomistic observation of disconnection-mediated grain boundary migration.

Nat Commun 2019 01 11;10(1):156. Epub 2019 Jan 11.

Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, 15261, USA.

Shear-coupled grain boundary (GB) migration is of general significance in the deformation of nanocrystalline and polycrystalline materials, but comprehensive understanding of the migration mechanism at the atomic scale remains largely lacking. Here, we systematically investigate the atomistic migration of Σ11(113) coherent GBs in gold bicrystals using a state-of-art in situ shear testing technique combined with molecular dynamic simulations. We show that shear-coupled GB migration can be realised by the lateral motion of layer-by-layer nucleated GB disconnections, where both single-layer and double-layer disconnections have important contributions to the GB migration through their frequent composition and decomposition. We further demonstrate that the disconnection-mediated GB migration is fully reversible in shear loading cycles. Such disconnection-mediated GB migration should represent a general deformation phenomenon in GBs with different structures in polycrystalline and nanocrystalline materials, where the triple junctions can act as effective nucleation sites of GB disconnections.
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http://dx.doi.org/10.1038/s41467-018-08031-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6329749PMC
January 2019

Consecutive crystallographic reorientations and superplasticity in body-centered cubic niobium nanowires.

Sci Adv 2018 07 6;4(7):eaas8850. Epub 2018 Jul 6.

Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261, USA.

Plasticity of metallic nanowires is often controlled by the activities of single deformation mode. It remains largely unclear whether multiple deformation modes can be activated in an individual metallic nanowire and how much plasticity they can contribute. In situ nanomechanical testing reveals a superior plastic deformation ability of body-centered cubic (BCC) niobium nanowires, in which a remarkable elongation of more than 269% is achieved before fracture. This superplastic deformation originates from a synergy of consecutively nucleated multiple reorientation processes that occur for more than five times via three distinct mechanisms, that is, stress-activated phase transformation, deformation twinning, and slip-induced crystal rotation. These three coupled mechanisms work concurrently, resulting in sequential reorientations and therefore superplastic deformation of Nb nanowires. Our findings reveal a superior mechanical property of BCC Nb nanowires through the close coordination of multiple deformation modes, which may have some implications in other metallic nanowire systems.
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http://dx.doi.org/10.1126/sciadv.aas8850DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6035040PMC
July 2018

Enhancing the Strength of Graphene by a Denser Grain Boundary.

ACS Nano 2018 05 19;12(5):4529-4535. Epub 2018 Apr 19.

National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing 210093 , China.

From a device application point of view, the extreme mechanical strength of graphene is highly desirable. However, the unavoidable polycrystalline nature of graphene films produced by chemical vapor deposition (CVD) leads to significant fluctuations in mechanical properties. Although the effects of atomic defects or grain boundaries (GBs) on mechanical strength have been widely studied and some modifications have been applied to enhance the stiffness of graphene, the problems of fragility as well as significantly reduced breaking strength arise. Here we report a systematic study on the effect of elastic modulus and breaking strength of CVD-derived graphene films with a controlled density and distribution of GBs. We find that graphene films become much stronger by hugely increasing the density of GBs without triple junctions (TJs) formed inside, in analogy to the two-dimensional (2D) plum pudding structures. The comprehensive performance with a 2D Young's modulus of 436 N/m (∼1.3 TPa) and 2D breaking strength of 43 N/m (∼128 GPa) can be achieved with the average grain size of 20 nm. Moreover, the existence of TJs will slightly reduce the strength in these GB structures. Due to defect types, the graphene films will show various tearing behaviors after indentation. All these mechanical studies of GBs provide a guideline to obtain the optimal performance of 2D materials through GB structure engineering.
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http://dx.doi.org/10.1021/acsnano.8b00869DOI Listing
May 2018

Discrete shear band plasticity through dislocation activities in body-centered cubic tungsten nanowires.

Sci Rep 2018 Mar 15;8(1):4574. Epub 2018 Mar 15.

Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, 15261, USA.

Shear band in metallic crystals is localized deformation with high dislocation density, which is often observed in nanopillar deformation experiments. The shear band dynamics coupled with dislocation activities, however, remains unclear. Here, we investigate the dynamic processes of dislocation and shear band in body-centered cubic (BCC) tungsten nanowires via an integrated approach of in situ nanomechanical testing and atomistic simulation. We find a strong effect of surface orientation on dislocation nucleation in tungsten nanowires, in which {111} surfaces act as favorite sites under high strain. While dislocation activities in a localized region give rise to an initially thin shear band, self-catalyzed stress concentration and dislocation nucleation at shear band interfaces cause a discrete thickening of shear band. Our findings not only advance the current understanding of defect activities and deformation morphology of BCC nanowires, but also shed light on the deformation dynamics in other microscopic crystals where jerky motion of deformation band is observed.
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http://dx.doi.org/10.1038/s41598-018-23015-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5854623PMC
March 2018

Tuning the Outward to Inward Swelling in Lithiated Silicon Nanotubes via Surface Oxide Coating.

Nano Lett 2016 09 22;16(9):5815-22. Epub 2016 Aug 22.

Woodruff School of Mechanical Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332, United States.

Electrochemically induced mechanical degradation hinders the application of Si anodes in advanced lithium-ion batteries. Hollow structures and surface coatings have been often used to mitigate the degradation of Si-based anodes. However, the structural change and degradation mechanism during lithiation/delithiation of hollow Si structures with coatings remain unclear. Here, we combine in situ TEM experiment and chemomechanical modeling to study the electrochemically induced swelling of amorphous-Si (a-Si) nanotubes with different thicknesses of surface SiOx layers. Surprisingly, we find that no inward expansion occurs at the inner surface during lithiation of a-Si nanotubes with native oxides. In contrast, inward expansion can be induced by increasing the thickness of SiOx on the outer surface, thus reducing the overall outward swelling of the lithiated nanotube. Moreover, both the sandwich lithiation mechanism and the two-stage lithiation process in a-Si nanotubes remain unchanged with the increasing thickness of surface coatings. Our chemomechanical modeling reveals the mechanical confinement effects in lithiated a-Si nanotubes with and without SiOx coatings. This work not only provides insights into the degradation of nanotube anodes with surface coatings but also sheds light onto the optimal design of hollow anodes for high-performance lithium-ion batteries.
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http://dx.doi.org/10.1021/acs.nanolett.6b02581DOI Listing
September 2016

Nanoscale origins of the damage tolerance of the high-entropy alloy CrMnFeCoNi.

Nat Commun 2015 Dec 9;6:10143. Epub 2015 Dec 9.

Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.

Damage tolerance can be an elusive characteristic of structural materials requiring both high strength and ductility, properties that are often mutually exclusive. High-entropy alloys are of interest in this regard. Specifically, the single-phase CrMnFeCoNi alloy displays tensile strength levels of ∼ 1 GPa, excellent ductility (∼ 60-70%) and exceptional fracture toughness (KJIc>200 MPa√m). Here through the use of in situ straining in an aberration-corrected transmission electron microscope, we report on the salient atomistic to micro-scale mechanisms underlying the origin of these properties. We identify a synergy of multiple deformation mechanisms, rarely achieved in metallic alloys, which generates high strength, work hardening and ductility, including the easy motion of Shockley partials, their interactions to form stacking-fault parallelepipeds, and arrest at planar slip bands of undissociated dislocations. We further show that crack propagation is impeded by twinned, nanoscale bridges that form between the near-tip crack faces and delay fracture by shielding the crack tip.
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http://dx.doi.org/10.1038/ncomms10143DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4682111PMC
December 2015

Size-Dependent Brittle-to-Ductile Transition in Silica Glass Nanofibers.

Nano Lett 2016 Jan 3;16(1):105-13. Epub 2015 Dec 3.

Department of Mechanical Engineering & Materials Science, University of Pittsburgh , Pittsburgh, Pennsylvania 15261, United States.

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.
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http://dx.doi.org/10.1021/acs.nanolett.5b03070DOI Listing
January 2016

High damage tolerance of electrochemically lithiated silicon.

Nat Commun 2015 Sep 24;6:8417. Epub 2015 Sep 24.

Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.

Mechanical degradation and resultant capacity fade in high-capacity electrode materials critically hinder their use in high-performance rechargeable batteries. Despite tremendous efforts devoted to the study of the electro-chemo-mechanical behaviours of high-capacity electrode materials, their fracture properties and mechanisms remain largely unknown. Here we report a nanomechanical study on the damage tolerance of electrochemically lithiated silicon. Our in situ transmission electron microscopy experiments reveal a striking contrast of brittle fracture in pristine silicon versus ductile tensile deformation in fully lithiated silicon. Quantitative fracture toughness measurements by nanoindentation show a rapid brittle-to-ductile transition of fracture as the lithium-to-silicon molar ratio is increased to above 1.5. Molecular dynamics simulations elucidate the mechanistic underpinnings of the brittle-to-ductile transition governed by atomic bonding and lithiation-induced toughening. Our results reveal the high damage tolerance in amorphous lithium-rich silicon alloys and have important implications for the development of durable rechargeable batteries.
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http://dx.doi.org/10.1038/ncomms9417DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4598720PMC
September 2015

Strong Hall-Petch Type Behavior in the Elastic Strain Limit of Nanotwinned Gold Nanowires.

Nano Lett 2015 Jun 12;15(6):3865-70. Epub 2015 May 12.

†Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 3700 O'Hara Street, Pittsburgh, Pennsylvania 15261, United States.

Pushing the limits of elastic deformation in nanowires subjected to stress is important for the design and performance of nanoscale devices from elastic strain engineering. Particularly, introducing nanoscale twins has proved effective in rising the tensile strength of metals. However, attaining ideal elastic strains in nanotwinned materials remains challenging, because nonuniform twin sizes locally affect the yielding behavior. Here, using in situ high-resolution transmission electron microscopy tensile testing of nanotwinned [111]-oriented gold nanowires, we report direct lattice-strain measurements that demonstrate a strong Hall-Petch type relationship in the elastic strain limit up to 5.3%, or near the ideal theoretical limit, as the twin size is decreased below 3 nm. It is found that the largest twin in nanowires with irregular twin sizes controls the slip nucleation and yielding processes in pure tension, which is in agreement with earlier atomistic simulations. Continuous hardening behavior without loss of strength or softening is observed in nanotwinned single-crystalline gold nanowires, which differs from the behaviors of bulk nanocrystalline and nanotwinned-nanocrystalline metals. These findings are of practical value for the use of nanotwinned metallic and semiconductor nanowires in strain-engineered functional microdevices.
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http://dx.doi.org/10.1021/acs.nanolett.5b00694DOI Listing
June 2015

In situ atomic-scale observation of twinning-dominated deformation in nanoscale body-centred cubic tungsten.

Nat Mater 2015 Jun 9;14(6):594-600. Epub 2015 Mar 9.

1] Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA [2] Department of Materials Science and Engineering and State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China.

Twinning is a fundamental deformation mode that competes against dislocation slip in crystalline solids. In metallic nanostructures, plastic deformation requires higher stresses than those needed in their bulk counterparts, resulting in the 'smaller is stronger' phenomenon. Such high stresses are thought to favour twinning over dislocation slip. Deformation twinning has been well documented in face-centred cubic (FCC) nanoscale crystals. However, it remains unexplored in body-centred cubic (BCC) nanoscale crystals. Here, by using in situ high-resolution transmission electron microscopy and atomistic simulations, we show that twinning is the dominant deformation mechanism in nanoscale crystals of BCC tungsten. Such deformation twinning is pseudoelastic, manifested through reversible detwinning during unloading. We find that the competition between twinning and dislocation slip can be mediated by loading orientation, which is attributed to the competing nucleation mechanism of defects in nanoscale BCC crystals. Our work provides direct observations of deformation twinning as well as new insights into the deformation mechanism in BCC nanostructures.
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http://dx.doi.org/10.1038/nmat4228DOI Listing
June 2015

Formation of monatomic metallic glasses through ultrafast liquid quenching.

Nature 2014 Aug 6;512(7513):177-80. Epub 2014 Aug 6.

Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.

It has long been conjectured that any metallic liquid can be vitrified into a glassy state provided that the cooling rate is sufficiently high. Experimentally, however, vitrification of single-element metallic liquids is notoriously difficult. True laboratory demonstration of the formation of monatomic metallic glass has been lacking. Here we report an experimental approach to the vitrification of monatomic metallic liquids by achieving an unprecedentedly high liquid-quenching rate of 10(14) K s(-1). Under such a high cooling rate, melts of pure refractory body-centred cubic (bcc) metals, such as liquid tantalum and vanadium, are successfully vitrified to form metallic glasses suitable for property interrogations. Combining in situ transmission electron microscopy observation and atoms-to-continuum modelling, we investigated the formation condition and thermal stability of the monatomic metallic glasses as obtained. The availability of monatomic metallic glasses, being the simplest glass formers, offers unique possibilities for studying the structure and property relationships of glasses. Our technique also shows great control over the reversible vitrification-crystallization processes, suggesting its potential in micro-electromechanical applications. The ultrahigh cooling rate, approaching the highest liquid-quenching rate attainable in the experiment, makes it possible to explore the fast kinetics and structural behaviour of supercooled metallic liquids within the nanosecond to picosecond regimes.
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http://dx.doi.org/10.1038/nature13617DOI Listing
August 2014

Void-assisted plasticity in Ag nanowires with a single twin structure.

Nanoscale 2014 Aug;6(16):9574-8

School of Physics and Technology, Center for Electron Microscopy and MOE Key Laboratory of Artificial Micro- and Nano-structures, Wuhan University, Wuhan 430072, China.

By employing the in situ transmission electron microscopy (TEM) technique, tensile deformation behaviors of a silver nanowire (NW) with a single twin structure were studied. Our observations revealed that the initial stage of plastic deformation was dominated by surface-mediated partial dislocation activities. Strikingly, the void formation and growth were shown to govern the later stage of plasticity, leading to the ductile type of fracture in NWs. Possible void nucleation and growth mechanisms were discussed. Additionally, TEM images show the transformation from bi-crystal to polycrystal in the fracture area, likely due to the void activity. Our results have implications in the assembly of functional structures applying nano-building blocks.
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http://dx.doi.org/10.1039/c3nr04731hDOI Listing
August 2014

Screening for acute HIV infections and estimating HIV incidence among female sex workers from low-grade venues in Guangxi, China.

PLoS One 2014 11;9(6):e99522. Epub 2014 Jun 11.

Guangxi Center for Disease Control and Prevention, Nanning, China.

Background: Guangxi has become one of the provinces with the most severe HIV-1 epidemic in China, where heterosexual contact is the dominant transmission route. However, data of acute HIV infections and HIV incidence among female sex workers (FSWs) from low-grade venues are scant.

Methods: A cross-sectional survey was performed among FSWs from low-grade venues in Guangxi. HIV antibody screening was performed by rapid testing (RT). HIV antibody-negative specimens were screened by pooled nucleic acid amplification testing (NAAT) for acute HIV infections. HIV antibody-positive specimens were further analyzed by Western blot (WB), followed by an HIV-1 BED capture enzyme immunoassay (BED-CEIA) to identify the recent infections. HIV-1 incidence was estimated by the data of pooled NAAT and BED-CEIA, respectively.

Results: A total of 7936 FSWs were recruited and answered the questionnaires. We successfully collected the blood samples from 6469 (81.5%) participants, of which 139 (2.1%) were HIV antibody-positive and 6330 (97.9%) were HIV antibody-negative by RT. With pooled NAAT, 7 cases were found to be HIV RNA positive, representing an additional 5.0% of HIV-infected persons and an estimated HIV incidence of 1.45 (95% CI: 1.17-1.76) per 100 person years. There were 137 positive and 2 indeterminate by WB, of which 124 (90.5%) positive specimens were subjected to BED-CEIA testing identifying 28 recent infections. The HIV incidence determined by BED-CEIA testing was 1.04 (95% CI: 0.65-1.43) per 100 person years. The overall prevalence of HIV among FSWs from low-grade venues in Guangxi was 2.2% (95% CI: 1.9-2.6).

Conclusions: We found that the addition of HIV RNA screening to routine HIV antibody testing significantly improved the detection of HIV infection among FSWs from low-grade venues in Guangxi. Our findings also provided the useful baseline data of HIV incidence among this population for targeting local HIV prevention, intervention, monitoring and treatment.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0099522PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4053442PMC
October 2015

[The role of RNA pooling technique in the diagnosis of acute HIV infection and the estimation on HIV incidence among low-grade-venues female sex workers].

Zhonghua Liu Xing Bing Xue Za Zhi 2014 Mar;35(3):259-61

Division of HIV/AIDS Prevention and Control, Guangxi Zhuang Autonomous Region Center for Disease Control and Prevention, Nanning 530028, China. Email:

Objective: To examine the feasibility of RNA pooling technique in the diagnosis on acute HIV infection among female sex workers (FSWs) working at the low-grade venues.

Methods: Plasma samples from the low-grade-venue FSWs in Guangxi, in 2011 were tested for HIV antibody using the rapid testing method. All samples which were HIV antibody negative in the rapid testing were tested for HIV RNA with RNA pooling technique. FSWs who showed HIV RNA positive were tested for HIV antibody by Western blot method in 3 months. The HIV incidence in the low-grade venue FSWs was counted under the estimation formula.

Results: There were 6 469 cases of FSWs who were recruited in this study. Through rapid testing, results showed that HIV antibody was positive in 139 cases, with the positive rate as 2.15%. 6 330 FSWs with HIV antibody negative were tested by HIV RNA pooling method, with 7 of them showing HIV RNA positive, in which 6 cases showed HIV-1 antibody seroconversion, thus were diagnosed as acute HIV infection. HIV incidence in low-grade FSWs appeared to be 1.45 per 100 person years (95%CI:1.17-1.76 per 100 person years) in Guangxi.

Conclusion: Other than regular routine HIV antibody testing, it seemed necessary to adopt the HIV RNA pooling strategy in high-risk groups such as FSWs, so as to early detect the HIV infection and to timely perform the intervention or treatment programs to prevent sexual transmission of HIV.
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March 2014
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