arXiv subjects

Geri Topore

Publications and source records attributed to Geri Topore.

7 recordsLinked to original sources

arXiv2026

Polar Topologies in a Ferroelastic Metal Membrane

Polar metals, materials in which electric polarisation and metallicity coexist, are exceptionally rare because itinerant electrons screen long-range dipoles and favour centrosymmetric structures. Engineering polar textures in a conducting magnet holds promise for reconfigurable spin orbit coupling and magnetoelectric functionality. Here we show that releasing epitaxial SrRuO3 films from their substrates drives a hierarchy of ferroelastic domain refinement from micrometre to nanometre length scales, and that this structural reorganisation spontaneously generates two distinct classes of emergent polar texture that are ubiquitous across the freestanding membrane. Using correlative microscopy from mesoscale electron channelling contrast imaging (ECCI) to atomic resolution scanning transmission electron microscopy (STEM), we demonstrate that electric polarisation emerges selectively at translation-inequivalent antiphase boundaries (APBs). At these boundaries multicomponent aac tilt field undergoes Neel-like interpolation that preserves the in-phase tilt component and amplifies roto flexoelectric coupling, while translation-equivalent boundaries remain nonpolar. The Neel like interpolation at hard APBs and Ising like collapse of all tilt components at easy APBs is corroborated with ab initio calculations. While embedded 90 ferroelastic walls provide an additional mechanistically distinct source of electric polarisation resulting in polar nanoclusters (4 nm). These distinct nanotextures at 90 walls from via elastic accommodation of strain mismatch between variants and rotostriction as the tilt field interpolates across the boundaries. These findings show that, in a membrane form, metal oxides provide a robust platform for hosting nanoscale ferroelastic domains that generate polar textures.

cond-mat.mtrl-sci↗

arXiv2026

Helium-Cooled Cryogenic STEM Imaging and Ptychography for Atomic-Scale Study of Low-Temperature Phases

Much of the exotic functionality of prime interest in quantum materials emerges from structural and electronic ground states that can only be accessed at cryogenic temperatures. Understanding device operation therefore requires structural characterization under the same low-temperature conditions at which these functional phases exist, as room-temperature measurements often probe a different structural state. Achieving atomic-resolution in scanning transmission electron microscopy imaging and particularly 4D-STEM electron ptychography at liquid helium temperature has remained extremely challenging because even small amounts of drift, vibration, and thermal instability associated with the cryogen can disrupt the stringent stability requirements of atomic-resolution STEM. In this work we demonstrate atomic-resolution STEM and multislice electron ptychography at temperatures as low as 20 K using a commercial helium cooled holder. We find that rapid scans and a multi-stage registration workflow are critical to reducing artifacts associated with cryogenic instability for atomic-resolution imaging, while for ptychography scan position correction including compensation for coupling between probe aberrations and position refinement is necessary for successful reconstructions. Together these results establish a pathway for reliable atomic-resolution STEM and ptychography at low temperature, enabling direct visualization of structural ground states relevant to quantum technology.

cond-mat.mtrl-sci↗

arXiv2025

Polarization Domain Mapping From 4D-STEM Using Deep Learning

Polarization in ferroelectric domains arises from atomic-scale structural variations that govern macroscopic functionalities. The interfaces between these domains known as domain walls host distinct physical responses, making their identification and control critical. Four dimensional scanning transmission electron microscopy (4DSTEM) enables simultaneous acquisition of real and reciprocal-space information at the atomic scale, offering a powerful platform for domain mapping. However, conventional analyses rely on computationally intensive processing and manual interpretation, which are time consuming and prone to misalignment and diffraction artefacts. Here, we present a convolutional neural network that, with minimal training, classifies polarization directions from diffraction data and segments domains in real space. We further introduce an adaptive sampling strategy that prioritizes images from domain wall regions, reducing the number of training images required while improving accuracy and interpretability. We demonstrate this approach for domain mapping in ferroelectric boracite, Cu3B7O13Cl.

cond-mat.mtrl-sci↗

arXiv2025

Programmable Beam Control for Electron Energy-Loss Spectroscopy and Ptychography

Programmable electron-beam scanning offers new opportunities to improve dose efficiency and suppress scan-induced artifacts in scanning transmission electron microscopy. Here, we systematically benchmark the impact of non-raster trajectories, including spiral and multi-pass sequential patterns, on two dose sensitive techniques: electron energy-loss spectroscopy (EELS) and ptychography. Using DyScO3 as a model perovskite, we compare spatial resolution, spectral fidelity, and artifact suppression across scan modes. Ptychographic phase reconstructions consistently achieve atomic resolution and remain robust to large jumps in probe position. In contrast, atomic-resolution EELS maps show pronounced sensitivity to probe motion, with sequential and spiral scans introducing non-uniform elemental contrast. Finally, spiral scanning applied under cryogenic conditions in BaTiO3 thin films improves dose uniformity and mitigates drift related distortions. These results establish practical guidelines for the implementation of programmable scan strategies in low-dose 4D-STEM and highlight the inherent resilience of ptychography to trajectory-induced artifacts.

cond-mat.mtrl-sci↗

arXiv2025

Degradation and SEI Evolution in Alloy Anodes Revealed by Correlative Liquid-Cell Electrochemistry and Cryogenic Microscopy

Understanding solid liquid interfaces at high spatial and chemical resolution is crucial for advancing electrochemical energy storage technologies, yet this remains a persistent challenge due to the lack of characterisation techniques that can capture dynamic processes and preserve fragile interfacial chemistries. In lithium ion batteries, interfacial phenomena such as lithium alloying, solid electrolyte interphase formation, and electrode degradation play a decisive role in capacity retention and failure mechanisms but are difficult to observe in their native state due to high mobility, reactivity, and low atomic number of lithium. Here, we use a recently introduced correlative operando characterisation approach that integrates electrochemical liquid cell transmission electron microscopy with cryogenic atom probe tomography to resolve the evolution of a platinum alloy anode at the solid liquid interface during electrochemical cycling. This correlative, cryo enabled workflow reveals spatially heterogeneous SEI formation, the presence of lithium carbonate rich inner SEI layers, and the retention of elemental lithium within the platinum electrode, most likely trapped along grain boundaries. Additionally, we observe the formation of mossy lithium structures and irreversible lithium loss through dead lithium accumulation. Our results provide direct mechanistic insight into lithium alloying and degradation pathways in alloy based anodes and establish a generalised platform for probing dynamic electrochemical interfaces with complementary structural and chemical sensitivity. The methodology is broadly applicable to next generation electrode materials and electrochemical devices where interfacial dynamics dictate performance and stability.

cond-mat.mtrl-sci↗

arXiv2025

Navigating Chiral Spin Architectures in Non-Collinear Antiferromagnetic Thin Films

Noncollinear antiferromagnets offer much promise for antiferromagnetic spintronics and neuromorphic applications with a plethora of functional properties surpassing many competing magnetic systems. Films grown on mismatched substrates may relieve strain by the creation of slip-plane defects that strongly manipulate global physical properties important for application. This work demonstrates that a post growth annealing strategy results in near-defect-free, structurally robust films that reveal the underlying thermal evolution of the magnetic order symmetry. Beyond a critical film thickness, the spin structure transitions between two right-handed irreducible chiral representations via left-handed chiral ordering producing a striking change in the sign and angular dependence of the Anomalous Hall coefficient. The previously established mechanism of spin rotations in the (111) plane cannot fully explain the transition in applied magnetic field, and using a macrospin model this work finds that rotations along the chirality-inverting [1-10] direction are energetically preferable under certain conditions. These observations suggest that both left-handed and right-handed chiral order can be accessed in a single system, opening new routes to engineer devices by controlled switching of magnetic chirality allowing selection of associated functional properties as governed by symmetry.

cond-mat.mtrl-sci↗

arXiv2025

A Workflow for Correlative in-situ Nano-chip Liquid Cell Transmission Electron Microscopy and Atom Probe Tomography Enabled by Cryogenic Plasma Focused Ion Beam

Operando/in-situ liquid cell transmission electron microscopy (LCTEM) allows for real time imaging of dynamic nanoscale liquid-based processes. However, due to the thick liquid cell of traditional LCTEM holders and thus scattering of the electron beam passing through the cell, the achievable spatial and chemical resolution is limited. Cryogenic atom probe tomography (cryo-APT) overcomes these limitations by offering (near-)atomic scale compositional analysis of frozen liquid-solid interfaces. However, APT provides limited structural analysis and has no capacity for dynamic or operando liquid cell studies. This work presents a novel workflow for site-specific cryo-APT sample preparation of liquid-solid interfaces from in-situ electrochemical LCTEM Micro-Electro-Mechanical Systems (MEMS) chips. Using cryogenic inert gas transfer suitcase and a cryogenic plasma-focused ion beam (PFIB), a MEMs nanochip containing a Li electrolyte from an electrochemistry LCTEM holder was successfully frozen, transferred to the cryo stage of a PFIB and prepared into APT needle samples containing the electrolyte-electrode interface at cryogenic temperatures, followed by cryogenic transfer to an atom probe for nanoscale compositional analysis. This correlative approach provides dynamic nanoscale imaging and near atomic scale compositional analysis of liquid-solid interfaces. This method enables reliable and reproducible APT sample preparation of these frozen interfaces from MEMs based nanochips and can hence be used across materials systems and energy-conversion or storage devices.

cond-mat.mtrl-sci↗