arXiv subjects

Haozhi Sha

Publications and source records attributed to Haozhi Sha.

9 recordsLinked to original sources

arXiv2026

Operando spectro-ptychography reveals dynamical charge-storage and degradation pathways in redox-active electrodes

Electrochemical reactions at buried electrode-electrolyte interfaces govern how redox-active materials store and release energy. However, these reactions are difficult to visualize because chemical and morphological changes occur simultaneously over distinct length and time scales. Existing operando microscopies often require trade-offs among chemical sensitivity, spatial resolution and temporal resolution. Direct nanoscale tracking of such processes throughout extended timescale has therefore remained out of reach. Here, we develop a fast and robust operando soft X-ray spectro-ptychography platform that delivers chemical-state-resolved spatiotemporal movies of redox-active electrodes over the full battery lifetime. Applied to an alkaline Fe anode, the method reveals that reversible charge storage gives way to degradation through two competing processes: rapid hydroxide insertion that drives early reversible cycling, and slower dissolution-redeposition that redistributes Fe, enlarges FeOOH particles, and ultimately causes capacity loss. By separating fast charge-storage chemistry from slower degradation chemistry in operando and at both single-particle and particle ensemble level, this work establishes spectro-ptychography as a general approach for studying dynamic redox transformations in batteries, electrocatalysts, and other electrochemical materials.

cond-mat.mtrl-sci↗

arXiv2026

Three-dimensional imaging of individual carbon atoms

Carbon is fundamental to science and technology due to its diverse bonding configurations, structural versatility, and essential role in defining the mechanical, chemical, electronic, and quantum properties of materials. However, direct three-dimensional (3D) imaging of individual carbon atoms remains a long-standing challenge. Here, we use twisted bilayer graphene (TBG) as a model system and demonstrate ptychographic atomic electron tomography (pAET) for determining the 3D atomic coordinates of individual carbon atoms with a precision of 0.11 angstrom. The resulting 3D atomic model uncovers chiral lattice distortions driven by van der Waals interactions that exhibit meron-like and skyrmion-like structural textures. These findings provide direct insight into the interplay between 3D chiral lattice deformation and electronic properties in moire-engineered carbon systems. Beyond TBG, pAET offers a versatile approach for 3D atomic-scale imaging of carbon-based and other light-element materials that are central to advances in physics, chemistry, materials science, and nanotechnology.

cond-mat.mtrl-sci↗

arXiv2025

Imaging thick objects with deep-sub-angstrom resolution and deep-sub-picometer precision

Size effects are ubiquitous in the structural, mechanical, and physical properties of materials, making it highly desirable to study the intrinsic properties of thick objects through high-resolution structural analysis in transmission electron microscopy. Although deep-sub-angstrom resolution has been achieved with multislice electron ptychography, the sample thickness is typically very limited. By combining energy filtering and extended local-orbital ptychography (eLOP) that retrieves varying aberrations during electron scanning, here we report ptychographic reconstructions for silicon as thick as 85 nm, approximately three times larger than usual thickness threshold for conventional multislice electron ptychography. The elimination of aberration variations contributes to accurate reconstructions with an information limit of 18 pm and atomic position precision of 0.39 pm. Accurate ptychographic reconstructions for thick objects can facilitate the discovery or interpretation of intrinsic structural and physical phenomena in solids, which is of great significance in physics, chemistry, materials science, and semiconductor device engineering.

cond-mat.mtrl-sci↗

arXiv2024

High-quality imaging of large areas through path-difference ptychography

Tilting planar samples for multi-zone-axes observation is a routine procedure in electron microscopy. However, this process invariably introduces optical path differences in the electron beam across different sample positions, significantly compromising image quality, particularly over large fields of view. To address this challenge, we developed path difference ptychography (PDP), a method capable of decoupling path differences from the four-dimensional data during reconstruction. This enables the acquisition of high-quality, large-scale images, facilitating a more comprehensive understanding and analysis of materials microstructure. Moreover, PDP has the potential to promote the widespread application of ptychographic tomography in the analysis of planar samples.

cond-mat.mtrl-sci↗

arXiv2024

Imaging, counting, and positioning single interstitial atoms in solids

Interstitial atoms are ubiquitous in solids and they are widely incorporated into materials to tune their lattice structure, electronic transportation, and mechanical properties. Because the distribution of interstitial atoms in matrix materials is usually disordered and most of them are light atoms with weak scattering ability, it remains a challenge to directly image single interstitial atoms and measure their geometrical positions. In this work, direct imaging and measuring of single interstitial atoms have been realized with adaptive-propagator ptychography. The measurement of their three-dimensional coordinates enables quantitative analysis of the pair distribution function of the interstitial atoms and reveals the anisotropic occupation of oxygen in the interstitial sites in titanium. The current work paves the way for the determination of interstitial atoms in materials, and for the correlation between the atomic-scale behavior of interstitial atoms and the physical properties of materials.

cond-mat.mtrl-sci↗

arXiv2024

Three-dimensional imaging of buried heterointerfaces

We report three-dimensional (3D) structure determination of a twisted hexagonal boron nitride (h-BN) heterointerface from a single-view data set using multislice ptychography. We identify the buried heterointerface between two twisted h-BN flakes with a lateral resolution of 0.57 Å and a depth resolution of 2.5 nm. The latter is a significant improvement (~2.7 times) over the aperture-limited depth resolution of incoherent imaging modes such as annular-dark-field scanning transmission electron microscopy. This is attributed to the diffraction signal extending beyond the aperture edge with the depth resolution set by the curvature of the Ewald sphere. Future advances to this approach could improve the depth resolution to the sub-nanometer level and enable the identification of individual dopants, defects and color centers in twisted heterointerfaces and other materials.

cond-mat.mtrl-sci↗

arXiv2024

Polar vortex hidden in twisted bilayers of paraelectric SrTiO3

Polar topologies, such as vortex and skyrmion, have attracted significant interest due to their unique physical properties and promising applications in high-density memory devices. Currently, most polar vortices are observed in heterostructures containing ferroelectric materials and constrained by substrates. In this study, we unravel arrays of polar vortices formed in twisted freestanding bilayers composed of SrTiO3, a quantum-paraelectric material. Depth-resolved structures of the bilayers are measured with deep-sub-angstrom resolution and one picometer accuracy using multislice ptychography, enabling identification of the three-dimensional variations of polarization topology. Our findings reveal the evolution of the polar vortices in the twisted overlapping layers, demonstrating the reverse of rotation manner in the depth direction. Twisted freestanding bilayers provide a unique platform for exploration and modulation of novel polar topologies.

physics.app-ph↗

arXiv2023

Information limit of 15 pm achieved with bright-field ptychography

It is generally assumed that a high spatial resolution of a microscope requires a large numerical aperture of the imaging lens or detector. In this study, the information limit of 15 pm is achieved in transmission electron microscopy using only the bright-field disk (small numerical aperture) via multislice ptychography. The results indicate that high-frequency information has been encoded in the electrons scattered to low angles due to the multiple scattering of electrons in the objects, making it possible to break the diffraction limit of imaging via bright-field ptychography.

cond-mat.mtrl-sci↗

arXiv2022

Atomic-resolution imaging of magnetism via ptychographic phase retrieval

Atomic-scale characterization of spin textures in solids is essential for understanding and tuning properties of magnetic materials and devices. While high-energy electrons are employed for atomic-scale imaging of materials, they are insensitive to the spin textures. In general, the magnetic contribution to the phase of high-energy electron wave is 1000 times weaker than the electrostatic potential. Via accurate phase retrieval through electron ptychography, here we show that the magnetic phase can be separated from the electrostatic one, opening the door to atomic-resolution characterization of spin textures in magnetic materials and spintronic devices.

cond-mat.mtrl-sci↗