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Item type:Publication, Access status: with files , Evolution of length scales and of chemical heterogeneity during primary and secondary dealloyingWe study the evolution of silver-rich regions, or ‘clusters’, during the making of nanoporous gold by dealloying. The clusters, which are remnants of the master alloy that have evaded corrosion, impact the functional behavior of the material. Furthermore, they carry information on the structure size in the initial stages of dealloying. Using kinetic Monte Carlo simulations, we emulate electrochemical dealloying at various electrode potentials. Our simulations illustrate the two-stage character of the process, where primary dealloying generates the initial network of nanoscale ligaments, while the subsequent secondary dealloying is characterized by coarsening and further dissolution. Silver-rich clusters, embedded in essentially pure gold, form during primary dealloying throughout the range of dealloying potentials of the study. At this point, their size scales with that of the ligaments. Both sizes decrease with increasing dealloying potential, and the trends of size versus potential agree with a Gibbs-Thompson type relation. Yet, when coarsening increases the ligament size during secondary dealloying, the size of the silver clusters remains constant. Directly accessing the initial ligament size of nanoporous gold in experiment is challenging, yet our study links this size to that of the silver-rich clusters. The clusters survive even in the later stages of dealloying and their size can be measured. This provides an experimental signature of the initial size.Publicationtype: Journal ArticleScopus© Citations 10 103 429 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Scaling behavior of stiffness and strength of hierarchical network nanomaterials(2021-03-05); ; ; ; Structural hierarchy can enhance the mechanical behavior of materials and systems. This is exemplified by the fracture toughness of nacre or enamel in nature and by human-made architected microscale network structures. Nanoscale structuring promises further strengthening, yet macroscopic bodies built this way contain an immense number of struts, calling for scalable preparation schemes. In this work, we demonstrated macroscopic hierarchical network nanomaterials made by the self-organization processes of dealloying. Their hierarchical architecture affords enhanced strength and stiffness at a given solid fraction, and it enables reduced solid fractions by dealloying. Scaling laws for the mechanics and atomistic simulation support the observations. Because they expose the systematic benefits of hierarchical structuring in nanoscale network structures, our materials may serve as prototypes for future lightweight structural materials.Publicationtype: Journal Article125 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Datasets for the microstructure of nanoscale metal network structures and for its evolution during coarseningThe datasets in this work are files containing atom position coordinates of volume elements approximating nanoporous gold made by dealloying and annealing. The material is represented in an as-prepared state and in various stages of coarsening, as described in Phys. Rev. Mater, 3 (2019) 076001. Realistic initial structures of different solid fractions have been constructed by the leveled-wave algorithm, approximating mixtures at the end of early-stage spinodal decomposition. The microstructural evolution during coarsening by surface diffusion was approximated by on-lattice kinetic Monte-Carlo simulation. The data sets refer to solid fractions from 0.22 to 0.50, providing for different initial connectivity of the bicontinuous structures. Coarsening at two temperatures, 900 K and 1800 K, explores two different degrees of surface energy anisotropy – more faceted at 900 K and more rough at 1800 K. Each structure takes the form of a face-centred cubic lattice with approximately 32 million sites. A site can be occupied by either void or atom. 3D periodic boundary conditions are satisfied. Tables list each structure's properties, and specifically the specific surface area, two different measures for the ligament size, the net topological genus as well as the scaled genus. The atom coordinate files may serve as the basis for geometry analysis and for atomistic as well as finite element simulation studies of nanoporous as well as spinodally decomposed materials. The data sets are accessible via the TORE repository at http://hdl.handle.net/11420/3253.Publicationtype: Data PaperScopus© Citations 7 307 178 - Some of the metrics are blocked by yourconsent settings
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 51 396 290 - 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 16 333 325 - 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 Thesis544 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 24 112 103 - 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