The Experts below are selected from a list of 39096 Experts worldwide ranked by ideXlab platform
Horacio D Espinosa - One of the best experts on this subject based on the ideXlab platform.
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experimental computational investigation of zno nanowires strength and fracture
2009Co-Authors: Ravi Agrawal, Bei Peng, Horacio D EspinosaAbstract:An experimental and computational approach is pursued to investigate the fracture mechanism of [0001] oriented zinc oxide nanowires under uniaxial tensile loading. A MEMS-based Nanoscale Material testing stage is used in situ a transmission electron microscope to perform tensile tests. Experiments revealed brittle fracture along (0001) cleavage plane at strains as high as 5%. The measured fracture strengths ranged from 3.33 to 9.53 GPa for 25 different nanowires with diameters varying from 20 to 512 nm. Molecular dynamic simulations, using the Buckingham potential, were used to examine failure mechanisms in nanowires with diameters up to 20 nm. Simulations revealed a stress-induced phase transformation from wurtzite phase to a body-centered tetragonal phase at approximately 6% strain, also reported earlier by Wang et al. (1) The transformation is partial in larger nanowires and the transformed nanowires fail in a brittle manner at strains as high as 17.5%. The differences between experiments and computations are discussed in the context of (i) surface defects observed in the ZnO nanowires, and (ii) instability in the loading mechanism at the initiation of transformation.
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elasticity size effects in zno nanowires a combined experimental computational approach
2008Co-Authors: Ravi Agrawal, Bei Peng, Eleftherios Gdoutos, Horacio D EspinosaAbstract:Understanding the mechanical properties of nanowires made of semiconducting Materials is central to their application in nano devices. This work presents an experimental and computational approach to unambiguously quantify size effects on the Young’s modulus, E, of ZnO nanowires and interpret the origin of the scaling. A micromechanical system (MEMS) based Nanoscale Material testing system is used in situ a transmission electron microscope to measure the Young’s modulus of [0001] oriented ZnO nanowires as a function of wire diameter. It is found that E increases from ∼140 to 160 GPa as the nanowire diameter decreases from 80 to 20 nm. For larger wires, a Young’s modulus of ∼140 GPa, consistent with the modulus of bulk ZnO, is observed. Molecular dynamics simulations are carried out to model ZnO nanowires of diameters up to 20 nm. The computational results demonstrate similar size dependence, complementing the experimental findings, and reveal that the observed size effect is an outcome of surface reconstr...
Ravi Agrawal - One of the best experts on this subject based on the ideXlab platform.
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experimental computational investigation of zno nanowires strength and fracture
2009Co-Authors: Ravi Agrawal, Bei Peng, Horacio D EspinosaAbstract:An experimental and computational approach is pursued to investigate the fracture mechanism of [0001] oriented zinc oxide nanowires under uniaxial tensile loading. A MEMS-based Nanoscale Material testing stage is used in situ a transmission electron microscope to perform tensile tests. Experiments revealed brittle fracture along (0001) cleavage plane at strains as high as 5%. The measured fracture strengths ranged from 3.33 to 9.53 GPa for 25 different nanowires with diameters varying from 20 to 512 nm. Molecular dynamic simulations, using the Buckingham potential, were used to examine failure mechanisms in nanowires with diameters up to 20 nm. Simulations revealed a stress-induced phase transformation from wurtzite phase to a body-centered tetragonal phase at approximately 6% strain, also reported earlier by Wang et al. (1) The transformation is partial in larger nanowires and the transformed nanowires fail in a brittle manner at strains as high as 17.5%. The differences between experiments and computations are discussed in the context of (i) surface defects observed in the ZnO nanowires, and (ii) instability in the loading mechanism at the initiation of transformation.
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elasticity size effects in zno nanowires a combined experimental computational approach
2008Co-Authors: Ravi Agrawal, Bei Peng, Eleftherios Gdoutos, Horacio D EspinosaAbstract:Understanding the mechanical properties of nanowires made of semiconducting Materials is central to their application in nano devices. This work presents an experimental and computational approach to unambiguously quantify size effects on the Young’s modulus, E, of ZnO nanowires and interpret the origin of the scaling. A micromechanical system (MEMS) based Nanoscale Material testing system is used in situ a transmission electron microscope to measure the Young’s modulus of [0001] oriented ZnO nanowires as a function of wire diameter. It is found that E increases from ∼140 to 160 GPa as the nanowire diameter decreases from 80 to 20 nm. For larger wires, a Young’s modulus of ∼140 GPa, consistent with the modulus of bulk ZnO, is observed. Molecular dynamics simulations are carried out to model ZnO nanowires of diameters up to 20 nm. The computational results demonstrate similar size dependence, complementing the experimental findings, and reveal that the observed size effect is an outcome of surface reconstr...
Markus Valtiner - One of the best experts on this subject based on the ideXlab platform.
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in situ nano to microscopic imaging and growth mechanism of electrochemical dissolution e g corrosion of a confined metal surface
2017Co-Authors: Claudia Merola, Hsiuwei Cheng, Kai Schwenzfeier, Kai Kristiansen, Yingju Chen, Howard A Dobbs, Jacob N Israelachvili, Markus ValtinerAbstract:Reactivity in confinement is central to a wide range of applications and systems, yet it is notoriously difficult to probe reactions in confined spaces in real time. Using a modified electrochemical surface forces apparatus (EC-SFA) on confined metallic surfaces, we observe in situ nano- to microscale dissolution and pit formation (qualitatively similar to previous observation on nonmetallic surfaces, e.g., silica) in well-defined geometries in environments relevant to corrosion processes. We follow “crevice corrosion” processes in real time in different pH-neutral NaCl solutions and applied surface potentials of nickel (vs. Ag|AgCl electrode in solution) for the mica–nickel confined interface of total area ∼0.03 mm2. The initial corrosion proceeds as self-catalyzed pitting, visualized by the sudden appearance of circular pits with uniform diameters of 6–7 μm and depth ∼2–3 nm. At concentrations above 10 mM NaCl, pitting is initiated at the outer rim of the confined zone, while below 10 mM NaCl, pitting is initiated inside the confined zone. We compare statistical analysis of growth kinetics and shape evolution of individual Nanoscale deep pits with estimates from macroscopic experiments to study initial pit growth and propagation. Our data and experimental techniques reveal a mechanism that suggests initial corrosion results in formation of an aggressive interfacial electrolyte that rapidly accelerates pitting, similar to crack initiation and propagation within the confined area. These results support a general mechanism for Nanoscale Material degradation and dissolution (e.g., crevice corrosion) of polycrystalline nonnoble metals, alloys, and inorganic Materials within confined interfaces.
Bei Peng - One of the best experts on this subject based on the ideXlab platform.
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experimental computational investigation of zno nanowires strength and fracture
2009Co-Authors: Ravi Agrawal, Bei Peng, Horacio D EspinosaAbstract:An experimental and computational approach is pursued to investigate the fracture mechanism of [0001] oriented zinc oxide nanowires under uniaxial tensile loading. A MEMS-based Nanoscale Material testing stage is used in situ a transmission electron microscope to perform tensile tests. Experiments revealed brittle fracture along (0001) cleavage plane at strains as high as 5%. The measured fracture strengths ranged from 3.33 to 9.53 GPa for 25 different nanowires with diameters varying from 20 to 512 nm. Molecular dynamic simulations, using the Buckingham potential, were used to examine failure mechanisms in nanowires with diameters up to 20 nm. Simulations revealed a stress-induced phase transformation from wurtzite phase to a body-centered tetragonal phase at approximately 6% strain, also reported earlier by Wang et al. (1) The transformation is partial in larger nanowires and the transformed nanowires fail in a brittle manner at strains as high as 17.5%. The differences between experiments and computations are discussed in the context of (i) surface defects observed in the ZnO nanowires, and (ii) instability in the loading mechanism at the initiation of transformation.
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elasticity size effects in zno nanowires a combined experimental computational approach
2008Co-Authors: Ravi Agrawal, Bei Peng, Eleftherios Gdoutos, Horacio D EspinosaAbstract:Understanding the mechanical properties of nanowires made of semiconducting Materials is central to their application in nano devices. This work presents an experimental and computational approach to unambiguously quantify size effects on the Young’s modulus, E, of ZnO nanowires and interpret the origin of the scaling. A micromechanical system (MEMS) based Nanoscale Material testing system is used in situ a transmission electron microscope to measure the Young’s modulus of [0001] oriented ZnO nanowires as a function of wire diameter. It is found that E increases from ∼140 to 160 GPa as the nanowire diameter decreases from 80 to 20 nm. For larger wires, a Young’s modulus of ∼140 GPa, consistent with the modulus of bulk ZnO, is observed. Molecular dynamics simulations are carried out to model ZnO nanowires of diameters up to 20 nm. The computational results demonstrate similar size dependence, complementing the experimental findings, and reveal that the observed size effect is an outcome of surface reconstr...
E Getto - One of the best experts on this subject based on the ideXlab platform.
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a numerical fitting routine for frequency domain thermoreflectance measurements of Nanoscale Material systems having arbitrary geometries
2021Co-Authors: Ronald J Warzoha, Adam A Wilson, Brian F Donovan, Andrew N Smith, Trent Perry, Nenad Miljkovic, E GettoAbstract:In this work, we develop a numerical fitting routine to extract multiple thermal parameters using frequency-domain thermoreflectance (FDTR) for Materials having non-standard, non-semi-infinite geometries. The numerical fitting routine is predicated on either a 2D or 3D finite element analysis that permits the inclusion of non-semi-infinite boundary conditions, which cannot be considered in the analytical solution to the heat diffusion equation in the frequency domain. We validate the fitting routine by comparing it with the analytical solution to the heat diffusion equation used within the wider literature for FDTR and known values of thermal conductivity for semi-infinite substrates ( SiO 2, Al 2 O 3, and Si). We then demonstrate its capacity to extract the thermal properties of Si when etched into micropillars that have radii on the order of the pump beam. Experimental measurements of Si micropillars with circular and square cross sections are provided and fit using the numerical fitting routine established as part of this work. Likewise, we show that the analytical solution is unsuitable for the extraction of thermal properties when the geometry deviates significantly from the standard semi-infinite case. This work is critical for measuring the thermal properties of Materials having arbitrary geometries, including ultra-drawn glass fibers and laser gain media.
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a numerical fitting routine for frequency domain thermoreflectance measurements of Nanoscale Material systems having arbitrary geometries
2020Co-Authors: Ronald J Warzoha, Adam A Wilson, Brian F Donovan, Andrew N Smith, Trent Perry, Nenad Miljkovic, E GettoAbstract:In this work, we develop a numerical fitting routine to extract multiple thermal parameters using frequency-domain thermoreflectance (FDTR) for Materials having non-standard, non-semi-infinite geometries. The numerical fitting routine is predicated on either a 2-D or 3-D finite element analysis that permits the inclusion of non semi-infinite boundary conditions, which can not be considered in the analytical solution to the heat diffusion equation in the frequency domain. We validate the fitting routine by comparing it to the analytical solution to the heat diffusion equation used within the wider literature for FDTR and known values of thermal conductivity for semi-infinite substrates (SiO2, Al2O3 and Si). We then demonstrate its capacity to extract the thermal properties of Si when etched into micropillars that have radii on the order of the pump beam. Experimental measurements of Si micropillars with circular cross-sections are provided and fit using the numerical fitting routine established as part of this work. Likewise, we show that the analytical solution is unsuitable for the extraction of thermal properties when the geometry deviates significantly from the standard semi-infinite case. This work is critical for measuring the thermal properties of Materials having arbitrary geometries, including ultra-drawn glass fibers and laser gain media.
