Atomic-Level, Depth-Resolved 3D Imaging of Voids with Electron Ptychography

Nanoscale hollow and voided structures are ubiquitous in materials subjected to extreme environments, including fission and fusion reactor materials, accelerator components, and space materials [1–3]. These voids, often generated by high-energy photon, electron, or ion irradiation, can nucleate cracks and induce embrittlement, ultimately compromising structural integrity and durability. Atomic scale understanding of void structure, associated strain fields, and three-dimensional spatial distributions is therefore essential for elucidating damage mechanisms and guiding materials design. However, simultaneous access to both atomic resolution and three-dimensional information remain challenging with conventional electron microscopy techniques. Here, we apply multislice electron ptychography (MEP) to investigate hollow cobalt phosphide (CoP) nanoparticles formed via the Kirkendall effect [4]. MEP data are acquired from a single two-dimensional x–y scan, while depth information is recovered from the parallax of overlapping diffraction patterns, enabling three-dimensional structural reconstruction without sample tilting [5]. The entire dataset is collected within a few seconds, minimizing beam exposure and avoiding the need for a tilt series. While MEP for CoP nanoparticle achieves ∼0.3 Å lateral resolution, it simultaneously provides depth-resolved structural information in a dose-efficient manner, offering a clear advantage over conventional electron tomography for fragile hollow nanostructures [6]. MEP directly reveals the nucleation, growth, and termination of an internal void across the nanoparticle thickness within a single dataset. Atomic-resolution strain maps are extracted from individual ∼1 nm thick slices, enabling quantitative two-dimensional strain analysis at different depths and for voids of varying size (Figure 1). By extending this analysis along the beam direction, the full three-dimensional inner and outer surfaces of the CoP nanoparticle are reconstructed (Figure 2). Combined three-dimensional structural reconstruction and atomic-scale strain mapping at ∼0.3 Å lateral resolution provide new insights into Kirkendall-driven void formation and its local impact on the surrounding lattice, demonstrating the unique capability of multislice electron ptychography for studying voids and damage phenomena in materials relevant to extreme environments. Depth-resolved ptychographic imaging and atomic-scale strain mapping of a hollow CoP nanoparticle. (A) MEP reconstructions at selected depths (Z = 3–24 nm, each slice is 1-nm) showing the nucleation, growth, and disappearance of an internal void across the nanoparticle thickness. (B) Atomic-resolution in-plane strain maps extracted from a representative ∼2 nm thick slice, overlaid on the ptychographic phase image, revealing strain distributions surrounding the internal void. Three-dimensional reconstruction of the internal void in a CoP nanoparticle from MEP. (A) Reconstructed inner and outer surfaces viewed along the beam direction, showing the projected void morphology within the nanoparticle. (B) Oblique view highlighting the depth-dependent evolution of the internal void reconstructed from a single 2D x–y scan, illustrating the anisotropic 3D structure obtained without sample tilting.