Julia R. Greer

2026 marks the 95th anniversary of the Journal of Applied Physics. This paper samples the evolution and impact of JAP by highlighting one key paper from each of the journal's ten decades of publication.

Architected materials derive their high performance from geometry as much as from intrinsic material properties, yet most optimization frameworks search within predefined topology families, limiting the discovery of genuinely new morphologies. Here, we investigate whether superior architectures exist beyond the reach of these parameterized families, and demonstrate that they can be systematically discovered. We present a framework that searches directly in voxelated structural space. Cubic‐symmetric unit cells drawn from strut‐based, TPMS‐based, and hybrid families are encoded into a continuous latent representation, and surrogate‐guided multi‐objective search with an active learning loop repeatedly converts promising predictions into high‐fidelity validated data. Across nine rounds, the mean minimum Hamming distance from the initial dataset increases from 442 to 641 and the Pareto hypervolume rises from 0.106 to 0.113, confirming systematic expansion of the validated design domain. Computationally, the discovered architectures achieve 11–20% higher relative Young's modulus than initial designs at matched density. Fabricated via two‐photon polymerization and pyrolysis, the optimized carbon nano‐architectures outperform density‐matched counterparts by 18–23% in Young's modulus and 26–40% in strength, reaching specific stiffnesses of 17.2, 22.3, and 21.3 MPa m ³ kg ^{− 1} . These results establish that direct learning in structural space enables discovering mechanically efficient nano‐architectures beyond the initial parameterized families.

The interconnected pore structure and large surface-to-volume ratio of three-dimensional (3D) architected battery electrodes enable enhanced electrochemical performance through improved ionic transport. We developed a hydrogel infusion additive manufacturing (HIAM)-based approach to fabricate microarchitected LiFePO₄ (LFP)/C composite electrodes with feature dimensions of 18 μm, delivering a specific capacity of 160 mAh/g at C/10. Electrodes with tilted cube, honeycomb, and triply periodic minimal surface (TPMS) geometries were designed to probe geometric effects on electrochemical performance under various rates. Material characterization revealed homogeneous formation of LFP particles (201 ± 67 nm) within the lattices, while the concomitantly formed carbon network provided mechanical support and enabled high-fidelity architecture. An experimentally informed electrochemical model identified electrolyte Li⁺ transport and solid-state Li⁺ diffusion as the dominant factors governing active material utilization. This work introduces a versatile manufacturing platform for 3D battery components and provides insights into structure optimization for high-performance rechargeable batteries.

3D printing methods for small-scale metals enable a unique 10–100 nm dimensional niche where functional feature sizes, critical microstructural detail and atomic-level defects converge, challenging conventional hierarchical relationships and carrying significant nanomechanical implications. We introduce a metal nano-printing system combining two-photon lithography, hydrogel infusion-based additive manufacturing and in situ mechanical experiments on 3D nano-architected Ni, achieving ~100 nm critical dimensions, ~10 nm surface roughness, and a broad range of geometries (periodic vs. non-periodic; beam-based vs. shell-based) with superior specific strengths of ~100 MPa·g − 1·cm³ enabled by an unambiguous smaller is stronger size effect. Experiments identify concentrated-porosity regions as primary deformation-initiation sources and quantify their distribution as input for physics-informed, multiscale finite-element simulations that accurately predict size-dependent mechanical properties governed by nanoporosity-driven deformation. This work integrates experimental and computational approaches for the fabrication, characterization, and evaluation of nano- and micro-architected metals for nanotechnology and nanoscale manufacturing systems.

Hydrogel infusion‐based additive manufacturing (HIAM) is a chemically versatile solid‐state processing pathway that allows 3D structuring of ceramics and alloys with micro‐scale precision. Using thermal treatments of 3D‐printed metal ion‐infused gels, this process generates intricate microstructures throughout their complex phase evolution. Through investigation of the HIAM‐produced Cu _x Ni _1‐x alloy system, substantial grain growth after reduction is shown to drive the formation of numerous annealing twins and entrap unreduced oxide nano‐inclusions, resulting in hierarchical composite microstructures. These features appear to elevate the average nanoindentation hardnesses by up to four times that of bulk annealed Cu _x Ni _1‐x . Uniaxial compression of micropillars milled from individual grains reveals composition dependence on the scaling of the “smaller is stronger” size effect. This compositional dependence of deformation mechanisms arises from changes in reduction kinetics which influence the density of inclusions and voids developed by the HIAM process. This work highlights the rich microstructural landscape accessible to HIAM‐produced alloys and provides a useful pathway for the characterization and tuning of superior mechanical performance in additively manufactured alloys.

The complex morphological evolution of lithium metal at the solid-state electrolyte interface limits performance of solid-state batteries, leading to inhomogeneous reactions and contact loss. Inspired by biological morphogenesis, we developed an interfacial self-regulation concept in which a deformable secondary phase dynamically aggregates at the interface in response to local electro-chemo-mechanical stimuli, enhancing contact. The stripping of a lithium electrode that contains 5 to 20 mole % electrochemically inactive sodium domains causes spontaneous sodium accumulation across the interface, with the sodium deforming to attain intimate electrical contact without blocking lithium transport. This process, characterized with operando x-ray tomography and electron microscopy, mitigates voiding and improves cycling at low stack pressures. The counterintuitive strategy of adding electrochemically inactive alkali metal to improve performance demonstrates the utility of interfacial self-regulation for solid-state batteries.

Structural heterogeneity in solid-state batteries can impact the material utilization and fracture mechanisms. Crystallographically oriented LiCoO₂ film cathodes serve as a model electrode system for exploring how void distribution contributes to stress relief and buildup during cycling. Real- and reciprocal-space operando and ex situ synchrotron-based experiments are utilized to understand structural changes across multiple length scales that contribute to stress generation and fracture. Nanotomography uncovers a depth-dependent porosity variation in the pristine electrode and highlights the preferential fracture in regions of lower porosity during delithiation. Energy-dispersive X-ray diffraction and three-dimensional (3D) X-ray absorption near-edge spectroscopy (XANES) reveal the underutilization of cathode material in these regions. 3D XANES also confirms preferential delithiation near the subgrain boundaries. Chemo-mechanical modeling coupled with site-specific mechanical characterization demonstrates how stress accumulation in dense regions of the electrode leads to fracture and underutilization of active material. Our findings reveal the importance of material design to alleviate stress in small-volume changing cathodes.