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Item type:Publication, Access status: with files , Scalable fabrication and mechanical behaviour of hierarchical porous nickel networksAs the demand for light-weight structural and functional materials grows, the fabrication of hierarchical, high-performance micro- and nano-architectures becomes increasingly important. Here, we present a scalable alloying–dealloying strategy to fabricate porous metal with two- and three-level hierarchical networks (2 L-/3L-HN). By exploiting the vapour pressure difference between Ni and Zn, vapour phase alloying of Ni foam with Zn, followed by vapour phase dealloying of the resulting γ-Zn84Ni16 foam, generates a second hierarchical level, producing 2L-HN Ni or 2L-HN β-Zn50Ni50. Re-alloying 2L-HN β-Zn50Ni50 to 2L-HN γ-Zn84Ni16 via vapour phase alloying while preserving its hierarchical architecture enables chemical dealloying to create a third level of hierarchy at the nanoscale, producing 3L-HN Ni with significantly increased specific surface area. A novel scaling law is proposed to predict the mechanical properties of these hierarchical porous metallic networks as a function of solid fraction, and its validity is supported by compression tests on 2L-HN Ni with varying densities. This work establishes a scalable and versatile route for fabricating multiscale porous metallic networks with light-weight, tunable mechanical performance and high surface area.Publicationtype: Journal Article24 11 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Scaling behavior of Poisson's ratio in hierarchical nanoscale network materialsHierarchical nanoscale network materials have gained increasing interest over the last decade attributing to their enhanced functional and mechanical performance, combined with reduced density. However, investigations into their Poisson's ratio, a key fundamental mechanical property, remain lacking. In this work, monolithic hierarchical nanoporous gold with tunable structure size and solid volume fraction were prepared via a two-step electrochemical dealloying method. By using in-situ digital image correlation technique, we measured their elastic and plastic Poisson's ratios during macroscopic compression. The effects of solid fraction, upper level ligament size and strain were explored systematically. We found that both the elastic and plastic Poisson's ratios are independent of the upper level ligament size and compressive strain. Notably, we introduced a novel scaling law of elastic Poisson's ratio with solid fraction in hierarchical nanoscale network materials and verified it experimentally. This study addresses a knowledge gap in the mechanics of hierarchical nanoscale network materials, offering a comprehensive understanding of their structure–mechanical property relationships. This insight provides a foundation for the design of novel materials and the optimization of their functional and mechanical properties.Publicationtype: Journal Article42 23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Realizing nanostructure-enabled applications through dealloyed materials(2025-05-01); McCue, IanNanoporous metals produced via dealloying have attracted significant interest due to the interesting physics surrounding their morphological evolution and how their topologically complex structure influences mechanical, optical, and electrochemical properties. Their impressive nanostructure-enabled properties—such as increased catalytic activity, surface-enhanced Raman signals, high strength, and large surface-to-volume ratio—have led to catalysts, sensors, actuators, energy storage, and biomedical device coatings with superior properties and performance. However, translation of nanoporous metals into practical applications has revealed needs for new material systems and manufacturing approaches, and consequently better predictive models for application-specific operating conditions. The goal of this issue of MRS Bulletin is to elaborate on the latest advances in emerging methods and technologies of dealloyed materials that enable new structures and form factors, machine learning-guided design and synthesis, material recovery and sustainability for scaled-up production, and stable performance in intended operational environments.Publicationtype: Review Article8 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Compressive behavior and connecting topology of monolithic nanoporous niobium(Taylor & Francis, 2025); ; ; ; With an eye on the role of structure size and topology, this study explores the mechanical behavior of nanoporous (NP) Nb made by liquid-metal dealloying. Results from X-ray nanotomography and macro-compression tests confirm that coarsening degrades the yield strength and that Young's modulus deviates from scaling laws developed for NP Au made by dealloying in aqueous media. We find that the scaled genus of NP Nb is lower than what has been reported for NP Au, and this low connectivity provides an obvious explanation for the low modulus. Furthermore, the structural dispersion implies that additional structural descriptors should be acknowledged.Publicationtype: Journal Article38 16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Enhancing 3D reconstruction accuracy of FIB tomography data using multi-voltage images and multimodal machine learningFIB-SEM tomography is a powerful technique that integrates a focused ion beam (FIB) and a scanning electron microscope (SEM) to capture high-resolution imaging data of nanostructures. This approach involves collecting in-plane SEM images and using FIB to remove material layers for imaging subsequent planes, thereby producing image stacks. However, these image stacks in FIB-SEM tomography are subject to the shine-through effect, which makes structures visible from the posterior regions of the current plane. This artifact introduces an ambiguity between image intensity and structures in the current plane, making conventional segmentation methods such as thresholding or the k-means algorithm insufficient. In this study, we propose a multimodal machine learning approach that combines intensity information obtained at different electron beam accelerating voltages to improve the three-dimensional (3D) reconstruction of nanostructures. By treating the increased shine-through effect at higher accelerating voltages as a form of additional information, the proposed method significantly improves segmentation accuracy and leads to more precise 3D reconstructions for real FIB tomography data.Publicationtype: Journal Article76 127 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fast and efficient hard X-ray projection imaging below 10 nm resolution(Optica Publishing Group, 2024-08-12); ; ; High-resolution X-ray imaging of noncrystalline objects is often achieved through the approach of scanning coherent diffractive imaging known as ptychography. The imaging resolution is usually limited by the scattering properties of the sample, where weak diffraction signals at the highest scattering angles compete with parasitic scattering. Here, we demonstrate that X-ray multilayer Laue lenses with a high numerical aperture (NA) can be used to create a strong reference beam that holographically boosts weak scattering from the sample over a large range of scattering angles, enabling high-resolution imaging that is tolerant of such background. An imaging resolution of sub-10 nm was achieved at a photon energy of 17.4 keV with lenses of 0.014 NA from a Siemens star test object and a sample of hierarchical nanoporous gold, recording projection holograms at an effective magnification of more than 30,000 directly on a pixel-array detector. A numerical study compared this approach to low-NA far-field ptychography, indicating significant advantages for using high-NA lenses in the presence of background noise. This imaging modality is particularly fast and efficient at recording high-resolution transmission phase-contrast images over large fields of view in a facile manner.Publicationtype: Journal Article13 14 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Effects of structural hierarchy and size on mechanical behavior of nanoporous goldNanoporous gold with a hierarchical structure has prospects as an advanced functional material with enhanced mechanical properties, but how the hierarchical structure affects its mechanical properties compared to a unimodal structure has not been revealed. Here, we investigate the mechanical behavior of hierarchically-structured nanoporous gold and unimodally-structured nanoporous gold with the same relative density by micropillar compressive tests in dry and electrolyte environment. The ligament size at the upper-level structure in hierarchically-structured nanoporous gold and the ligament size in unimodally-structured nanoporous gold are kept similar, while having hierarchically-structured samples with ligament sizes of 10 to 50 nm at lower-level structure. We find that hierarchically-structured nanoporous gold shows greater compressive strength and pronounced stress-variation by oxidization of the surface compared to unimodally-structured nanoporous gold. A ligament-size dependency on the lower-level structure in hierarchical samples is observed, with compressive strength and stress variation by surface oxidation increasing as the lower-level ligament size decreases. Three-dimensionally reconstructed structure analysis suggests that the enhanced mechanical properties of hierarchically-structured nanoporous gold are attributed to the better-connected network of ligaments originating from two separated dealloying-coarsening procedures. The influence of dislocation activities depending on characteristic sizes is also discussed to elucidate the distinguished mechanical behavior.Publicationtype: Journal Article30 35 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Scaling between elasticity and topological genus for random network nanomaterialsWe explore the hypothesis that the variation of the effective, macroscopic Young's modulus, Eeff, of a random network material with its scaled topological genus, g, and with the solid fraction, φ, can be decomposed into the product of g- and φ-dependent functions. Based on findings for nanoporous gold, supplemented by the Gibson–Ashby scaling law for Eeff, we argue that both functions are quadratic in bending-dominated structures. We present finite-element-modeling results for Eeff of coarsened microstructures, in which g and φ are decoupled. These results support the quadratic forms.Publicationtype: Journal Article26 81 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Role of slice thickness quantification in the 3D reconstruction of FIB tomography data of nanoporous materials(Elsevier, 2024-02); ; ; ; In focused ion beam (FIB) tomography, a combination of FIB with a scanning electron microscope (SEM) is used for collecting a series of planar images of the microstructure of nanoporous materials. These planar images serve as the basis for reconstructing the three-dimensional microstructure through segmentation algorithms. However, the assumption of a constant distance between consecutively imaged sections is generally invalid due to random variations in the FIB milling process. This variation complicates the accurate reconstruction of the three-dimensional microstructure. Using synthetic FIB tomography data, we present an algorithm that repositions slices according to their actual thickness and interpolates the results using machine learning-based methods. We applied our algorithm to real datasets, comparing two standard approaches of microstructure reconstruction: on-the-fly via image processing and ruler-based via sample structuring. Our findings indicate that the ruler-based method, combined with our novel slice repositioning and interpolation algorithm, exhibits superior performance in reconstructing the microstructure.Publicationtype: Journal ArticleScopus© Citations 2 63 125 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Bulk nanoporous platinum for electrochemical actuationBulk nanoporous platinum (np-Pt) samples with a remarkably fine ligament size down to 2 nm and good mechanical robustness were fabricated for the first time by electrochemically dealloying Pt15Cu85 master alloy in 1 mol L−1 H2SO4 at 60 ℃. The as-prepared np-Pt shows an electrochemically active specific surface area as high as 25 m2/g due to the ultrafine nanostructure. The active surface area remains almost invariable even after 15% macroscopic compressive strain. Furthermore, np-Pt shows considerably high thermal stability due to the low surface diffusivity of Pt. Np-Pt is a promising surface- or interface-controlled functional material, particularly when excellent electrochemical and mechanical performance are necessary due to its high surface-to-volume ratio and mechanical robustness. This work demonstrated the potential application of np-Pt as an electrochemical actuation material. In-situ dilatometry experiments revealed that the surface adsorption–desorption of OH species on np-Pt causes significant strain variations. The proposed np-Pt electrochemical actuator shows an operating voltage down to 1.0 V, a large reversible strain amplitude of 0.37%, and a strain energy density of 1.64 MJ/m³.Publicationtype: Journal Article40 66