Yujun Xie

Overcoming the macroscopic brittleness of metallic glasses requires a fundamental understanding of shear banding mechanisms. However, characterizing the atomic-scale structural evolution within shear bands remains experimentally challenging due to the disordered nature of the material. Current characterization techniques typically yield statistically averaged or scalar information, failing to directly correlate local structural changes with shear-induced dilatation. In this study, we develop an image-recognition algorithm that allows quantitative analysis of high-resolution transmission electron microscopy image. This algorithm enables us to resolve the local structural evolution within shear bands. Analyses reveal that shear banding induces a collective expansion of local structural motifs with a volumetric dilatation of approximately 3%~7% by disintegration of dominant motifs within the amorphous structure. Crucially, distinct from thermally driven isotropic expansion, the structural evolution within shear bands exhibits intrinsic anisotropy. Thermodynamic and rheological assessments indicate that the material within the shear band reaches an enthalpy state and a viscosity level characteristic of a supercooled liquid. Previously assumed shear banding induced glass-to-liquid transition arises from the tensor nature of the applied stress that breaks structural symmetry and drives a directional transformation. These findings provide a quantitative understanding on the non-equilibrium structural dynamics governing localized plastic flow in disordered solids.

Solid polymer electrolytes (SPEs) endow Li metal batteries (LMBs) with high expectations, but their real-world applications suffer from the "seesaw effect" between mechanical robustness and ionic conductivity. Herein, inspired by the myofilament sliding, we propose a molecular muscle SPE consisting of mechanically interlocked [c2]daisy chain ([c2]DC) networks (^DCMINs) to break the SPE bottleneck, demonstrating a superior room-temperature (RT) ionic conductivity of 1.04 mS cm^-1 (no plasticizer) without sacrificing the mechanical properties. The dynamic [c2]DC units, in conjunction with host-guest interactions, strengthen the movement of soft poly(ethylene glycol) backbones that coordinate with Li ions to contribute to the improved Li-ion transport compared to the regular cross-linked polymer network. The intrinsically distinctive energy dissipation of ^DCMINs further facilitates the structural integrity of SPEs under the repeated deformation of Li metal anodes, restricting dendrite growth and thus ensuring a lifespan longer than 5000 h for Li symmetric cells. All-solid-state pouch LMBs (∼1 Ah) with muscle-inspired SPEs exhibit competitive performance at RT in terms of cycling stability (87.8% capacity retention after 750 cycles for the LiFePO₄ cell). We anticipate that our findings could spur investigations regarding high-performance SPE design for advanced solid-state batteries.

While an electron microscope offers crucial atomic-resolution insights into structure–property relationships, radiation damage severely limits its use on beam-sensitive materials like proteins and 2D materials. To overcome this challenge, we push beyond the electron dose limits of the conventional method by adapting principles from multi-image super-resolution that had been widely used in remote sensing. Our method fuses multiple low-resolution, sub-pixel-shifted views and enhances this reconstruction with a convolutional neural network that integrates features from synthetic, multi-angle observations. We developed a dual-path, attention-guided network for four-dimensional scanning transmission electron microscopy (4D-STEM) that achieves atomic-scale super-resolution from ultra-low-dose data. This provides robust atomic-scale visualization across amorphous, semi-crystalline, and crystalline beam-sensitive specimens. Systematic evaluations on representative materials demonstrate the comparable spatial resolution to conventional ptychography under ultra low-dose conditions. Our work one-step expands the capabilities of 4D-STEM, offering a new and generalizable method for the structural analysis of any radiation-vulnerable material.

Kerogen is a key source of hydrocarbon production through hydraulic fracturing. However, the direct correlation between the molecular structure and mechanical properties remains unclear. Here, we employ four-dimensional scanning transmission electron microscopy (4D-STEM) to reveal heterogeneities defined by the orientation of π-π stacking domains and amorphous regions in kerogen. We observed that the morphologies of π-π stacking domains vary with kerogen maturity, ranging from small, randomly oriented grains to larger, continuous structures. Furthermore, we conduct in situ 4D-STEM tensile testing to visualize the strain distribution across these structural heterogeneities and elucidate the governing deformation mechanisms of kerogen. Our results demonstrate different mechanical responses within kerogen, suggesting that π-π stacking domains contribute to brittleness, while amorphous regions promote ductility. We believe this innovative approach to assessing the correlation between local structural order and the mechanical properties of kerogen could lead to improved geological models for optimizing the hydraulic fracturing efficiency.