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Item type:Publication, Access status: with files , Topology evolution during coarsening of nanoscale metal network structures(American Physical Society (APS), 2019-07-31); ; ; Many experiments exploit curvature-driven, surface-diffusion-mediated coarsening for tuning the characteristic structure size of metal network structures made by dealloying, such as nanoporous gold. Here we study this process by kinetic Monte Carlo simulation. The initial microstructures are leveled Gaussian random fields, approximating spinodally decomposed mixtures, of different solid fraction φ. Earlier work establishes these structures as valid representations of the nanoporous gold microstructure. We find that the coarsening law for the characteristic spacing between the ligaments of the network is universal, whereas the time evolution of the characteristic ligament diameter is not. The expected time exponent 1/4 is confirmed by our simulation. Contrary to what may be expected based on continuum models, the degree of surface faceting or roughness has no apparent effect on the coarsening kinetics. In the time interval of our study, the network connectivity - as measured by a scaled density of topological genus - remains sensibly invariant for networks with φ≥0.3, consistent with previous reports of a self-similar evolution of the microstructure during coarsening. Yet, networks with lesser φ lose their connectivity on coarsening and can even undergo a percolation-to-cluster transition. This process is slow for φ only little below 0.3 and it accelerates in networks with lesser φ. The dependency of the connectivity evolution on φ may explain controversial findings on the microstructure evolution of nanoporous gold in experimental studies.Publicationtype: Journal ArticleScopus© Citations 51 399 293 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , X-ray studies of nanoporous gold : powder diffraction by large crystals with small holes(American Physical Society (APS), 2017-12-19); ; ; X-ray diffraction studies of nanoporous gold face the poorly understood diffraction scenario where large coherent crystals are riddled with nanoscale holes. Theoretical considerations derived in this study show that the ligament size of the porous network influences the scattering despite being quasi single crystalline. Virtual diffraction of artificially generated samples confirms the results but also shows a loss of long-range coherency and the appearance of microstrain due to thermal relaxation. Subsequently, a large set of laboratory X-ray investigations of nanoporous gold fabricated by different approaches and synthesis parameters reveal a clear correlation between ligament size and size of the coherent scattering domains as well as extremely high microstrains in samples with ligament sizes below 10 nm.Publicationtype: Journal ArticleScopus© Citations 16 337 326 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Elasticity and plasticity of nanoporous gold: implications of molecular dynamics simulations(2017); Molecular dynamics simulations of compression tests on virtual nanoporous gold samples created by mimicking spinodal decomposition via Monte Carlo simulations reveal an anomalously compliant and weak behavior. This behavior, while in good agreement with experimental data of millimeter-sized dealloyed nanoporous gold, changes drastically once the network connectivity is varied. Topological disorder due to nodal shift also impacts the effective behavior of the material. Yet, on top of the above-mentioned topological descriptors or the solid fraction, atomistic processes, such as dislocation activity and surface effects, must be taken into account in order to explain the observed behavior of the material.Publicationtype: Doctoral Thesis548 746 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , On the origin of the anomalous compliance of dealloying-derived nanoporous gold(Elsevier, 2016-11-24); ; ; ; The origin of the anomalously compliant behavior of nanoporous gold is studied by comparing the elasticity obtained from molecular dynamics (MD) and finite element method (FEM) simulations. Both models yield a compliance, which is much higher than the predictions of the Gibson-Ashby scaling relation for metal foams and thus confirm the influence of other microstructural features besides the porosity. The linear elastic FEM simulation also yields a substantially stiffer response than the MD simulation, which reveals that nonlinear elastic behavior contributes decisively to the anomalous compliance of nanoporous gold at small structure size.Publicationtype: Journal ArticleScopus© Citations 24 115 103 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Anomalous compliance and early yielding of nanoporous gold(Elsevier, 2015-05-21); ; ; ; We present a study of the elastic and plastic behavior of nanoporous gold in compression, focusing on molecular dynamics simulation and inspecting experimental data for verification. Both approaches agree on an anomalously high elastic compliance in the early stages of deformation, along with a quasi immediate onset of plastic yielding even at the smallest load. Already before the first loading, the material undergoes spontaneous plastic deformation under the action of the capillary forces, requiring no external load. Plastic deformation under compressive load is accompanied by dislocation storage and dislocation interaction, along with strong strain hardening. Dislocation-starvation scenarios are not supported by our results. The stiffness increases during deformation, but never approaches the prediction by the relevant Gibson-Ashby scaling law. Microstructural disorder affects the plastic deformation behavior and surface excess elasticity might modify elastic response, yet we relate the anomalous compliance and the immediate yield onset to an atomistic origin: the large surface-induced prestress induces elastic shear that brings some regions in the material close to the shear instability of the generalized stacking fault energy curve. These regions are elastically highly compliant and plastically weak.Publicationtype: Journal Article77