Mechanical and electrical failure of transparent nanowire Electrodes

Flexible transparent electrodes have to withstand large mechanical strains without sacrificing electrical performance. For such applications, silver nanowire (Ag NW) networks are highly promising as they combine mechanical flexibility with low sheet resistance and high optical transmittance. In order to improve the performance of such nanowire electrodes a microscopic understanding of the interplay between mechanical and electrical failure is required. This can be achieved by a combination of in situ (or interrupted) tensile tests in a scanning electron microscope (SEM) with 4-probe electrical measurements of the sheet resistence. Please click Additional Files below to see the full abstract

Wedge-shaped twins and pseudoelasticity in fcc metallic nanowires under bending

AbstractMolecular dynamics simulations were performed to study the deformation mechanisms of 〈110〉-oriented, faceted Cu and Au nanowires under bending along three different crystallographic directions. Independent of the bending direction, the stress field is characterized by a highly nonlinear elastic response, leading to a shift of the neutral fiber away from the central wire axis. The nanowires show ultra-high yield strengths, and the achievable large elastic strains directly influence the dislocation nucleation through the change of the unstable stacking fault energy. In agreement with theory and experiments on face-centered cubic 〈110〉 nanowires under uniaxial load, the tensile part of the wires exhibit deformation twinning, while plastic deformation in the compressed part takes place by slip of perfect dislocations. Independent of the bending direction, wire size, temperature and bending rate, all wires showed the formation of wedge-shaped twins. Upon instantaneous load removal, wires bent in two of the three directions showed spontaneous, pseudoelastic unbending. The findings of this study could be relevant for the design of flexible electronics and mechanical energy storage applications at the nanoscale

Unveiling the mechanisms of motion of synchro-Shockley dislocations in Laves phases

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Slip and deformation behavior in intermetallic Cobalt-Samarium phases

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Exploring the transfer of plasticity across Laves phase interfaces in a dual phase magnesium alloy

The mechanical behaviour of Mg-Al alloys can be largely improved by the formation of an intermetallic Laves phase skeleton, in particular the creep strength. Recent nanomechanical studies revealed plasticity by dislocation glide in the (Mg,Al)$_2$Ca Laves phase, even at room temperature. As strengthening skeleton, this phase remains, however, brittle at low temperature. In this work, we present experimental evidence of slip transfer from the Mg matrix to the (Mg,Al)$_2$Ca skeleton at room temperature and explore associated mechanisms by means of atomistic simulations. We identify two possible mechanisms for transferring Mg basal slip into Laves phases depending on the crystallographic orientation: a direct and an indirect slip transfer triggered by full and partial dislocations, respectively. Our experimental and numerical observations also highlight the importance of interfacial sliding that can prevent the transfer of the plasticity from one phase to the other.Comment: 23 pages, 8 figures, 1 tabl

Tailoring the plasticity of topologically close-packed phases via the crystals' fundamental building blocks

Brittle topologically close-packed precipitates form in many advanced alloys. Due to their complex structures little is known about their plasticity. Here, we present a strategy to understand and tailor the deformability of these complex phases by considering the Nb-Co {\mu}-phase as an archetypal material. The plasticity of the Nb-Co {\mu}-phase is controlled by the Laves phase building block that forms parts of its unit cell. We find that between the bulk C15-NbCo$_2$ Laves and Nb-Co {\mu}-phase, the interplanar spacing and local elastic modulus of the Laves phase building block change, leading to a strong reduction in hardness and elastic modulus, as well as a transition from synchroshear to crystallographic slip. Furthermore, as the composition changes from Nb$_6$Co$_7$ to Nb$_7$Co$_6$, the Co atoms in the triple layer are substituted such that the triple layer of the Laves phase building block becomes a slab of pure Nb, resulting in inhomogeneous changes in elasticity and a transition from crystallographic slip to a glide-and-shuffle mechanism. These findings open opportunities to purposefully tailor the plasticity of these topologically close-packed phases in bulk, but at the atomic scale of interplanar spacing and local shear modulus of the fundamental crystal building blocks in their large unit cells

Combined in situ mechanical testing and scale-bridging 3D analysis of nanoporous gold

In this work we present results on in situ small scale testing of nanoporous gold (npg) in scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By combining nano- and micromechanical testing of pillar structures with advanced tomographic imaging, a 3D characterization of the plastic deformation process in different states of deformation is achieved. For small strut sizes 360° electron tomography (ET) is applied enabling high quality reconstructions of the 3D morphology of npg without missing-wedge artefacts. Combining the geometric information with mechanical data from in situ testing in SEM and TEM the yield strength is precisely determined. Furthermore, the experimentally derived 3D data are used as input for large-scale molecular dynamics (MD) simulations in order to understand the role of strain localization and identify predominant defect processes. Please click Additional Files below to see the full abstract

Comprehensive phylogeny of ray-finned fishes (Actinopterygii) based on transcriptomic and genomic data

Our understanding of phylogenetic relationships among bony fishes has been transformed by analysis of a small number of genes, but uncertainty remains around critical nodes. Genomescale inferences so far have sampled a limited number of taxa and genes. Here we leveraged 144 genomes and 159 transcriptomes to investigate fish evolution with an unparalleled scale of data: >0.5 Mb from 1,105 orthologous exon sequences from 303 species, representing 66 out of 72 ray-finned fish orders. We apply phylogenetic tests designed to trace the effect of whole-genome duplication events on gene trees and find paralogy-free loci using a bioinformatics approach. Genome-wide data support the structure of the fish phylogeny, and hypothesis-testing procedures appropriate for phylogenomic datasets using explicit gene genealogy interrogation settle some long-standing uncertainties, such as the branching order at the base of the teleosts and among early euteleosts, and the sister lineage to the acanthomorph and percomorph radiations. Comprehensive fossil calibrations date the origin of all major fish lineages before the end of the Cretaceous.Fil: Hughes, Lily C.. National Museum of Natural History; Estados Unidos. The George Washington University; Estados UnidosFil: Ortí, Guillermo. National Museum of Natural History; Estados Unidos. The George Washington University; Estados UnidosFil: Huang, Yu. Beijing Genomics Institute; China. Chinese Academy of Sciences; República de ChinaFil: Sun, Ying. China National Genebank; China. Beijing Genomics Institute; ChinaFil: Baldwin, Carole C.. National Museum of Natural History; Estados UnidosFil: Thompson, Andrew W.. National Museum of Natural History; Estados Unidos. The George Washington University; Estados UnidosFil: Arcila, Dahiana. National Museum of Natural History; Estados Unidos. The George Washington University; Estados UnidosFil: Betancur, Ricardo. National Museum of Natural History; Estados Unidos. Universidad de Puerto Rico, Recinto de Rio Piedras; Puerto RicoFil: Li, Chenhong. Shanghai Ocean University; ChinaFil: Becker, Leandro Anibal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales.; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche; ArgentinaFil: Bellora, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales.; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche; ArgentinaFil: Zhao, Xiaomeng. Chinese Academy of Sciences; República de China. Beijing Genomics Institute; ChinaFil: Li, Xiaofeng. Chinese Academy of Sciences; República de China. Beijing Genomics Institute; ChinaFil: Wang, Min. Beijing Genomics Institute; ChinaFil: Fang, Chao. Chinese Academy of Sciences; República de ChinaFil: Xie, Bing. Bgi-shenzhen; ChinaFil: Zhoui, Zhuocheng. China Fisheries Association; ChinaFil: Huang, Hai. Hainan Tropical Ocean University; ChinaFil: Chen, Songlin. Yellow Sea Fisheries Research Institute Chinese Academy Of Fishery Science; ChinaFil: Venkatesh, Byrappa. A-star, Institute Of Molecular And Cell Biology;Fil: Shi, Qiong. Chinese Academy of Sciences; República de Chin