Scientific Events

Topological defects—dislocations, grain boundaries, and related features—play an essential role in determining the properties of crystalline materials. When crystallite or functional domain sizes shrink to the nanometer scale, these defects become dominant. To date, however, neither bottom‑up nor top‑down synthesis has provided a reliable means of controlling them. Here, we demonstrate delicate control over shell epitaxy on nanocrystals within thin films, producing three‑dimensionally organized nanocrystallites with uniform grain boundaries and associated defects. In these structures, the resulting 3D‑patterned strain field can be mapped with atomic precision and tuned to introduce targeted dislocations or disclinations. Using multiscale crystallography and spectroscopy, we show that the uniformity and discreteness of these defects provide a clear correlation between local structure and collective electrochemical performance—specifically, catalytic activity in oxygen evolution and reduction reactions. Finally, we outline how this nanocrystallite‑engineering approach is guiding the design of next‑generation functional materials for energy nanotechnology [more]

Understanding the geometry of nanomaterials at the atomic scale provides critical insights into local structural heterogeneities and their impact on functional properties. Since shapes vary from particle to particle, detailed analysis at the single-particle level is essential. In this talk, I will present a high-throughput pipeline that integrates deep learning-based segmentation with quantitative shape analysis of individual nanoparticles from high-resolution transmission electron microscopy (HRTEM) images. First, I will describe the application of convolutional neural networks (CNNs) to segment 727 HRTEM micrographs of cubic Co₃O₄ nanoparticles, enabling the extraction of shape descriptors from 441,067 particles. This automated workflow allows for population-wide statistical characterization, bridging local structural detail with large-scale analysis. Second, I will present a size-resolved shape analysis at subnanometer precision, highlighting a critical threshold, “onset radius”, that marks transitions in particle shape, such as surface faceting and a shift from thermodynamic to kinetic growth regimes. This bottom-up approach illustrates how machine learning and data-driven analysis can reveal previously unquantified trends, offering a generalizable framework for high-throughput materials characterization. [more]

Recent groundbreaking developments in aberration-corrected scanning transmission electron microscopy (STEM) combined with advanced vibrational electron energy-loss spectroscopy (EELS) techniques have fundamentally transformed the way atomic-scale lattice dynamics and phonon behaviors are studied. In this seminar, I will highlight our seminal work in developing and applying state-of-the-art, spatially and momentum-resolved vibrational EELS methodologies to directly visualize phonon modes at atomic resolution. Our approach enables the unprecedented observation of localized phonon phenomena at individual defects, interfaces, and nanostructures, profoundly advancing our understanding of phonon-defect interactions, thermal boundary conductance, and electron–phonon coupling in materials. I will present key examples from our recent studies, including the direct imaging of defect-localized vibrational modes, nanoscale mapping of interfacial phonons, and quantification of phonon momentum distributions in quantum dots and phonon-electron coupling at superconducting interfaces. These insights provide critical foundations for addressing fundamental challenges in thermal management, quantum materials engineering, and solid-state ionic devices. Ultimately, our innovations offer powerful tools to elucidate and engineer the atomic-scale behaviors that dictate the performance of next-generation functional materials and systems. [more]

Microstructures in many engineering alloys are predominantly influenced by solid-state phase transformations that occur during industrial processing; these transformations almost always proceed by nucleation and growth. Quantitative modelling of the process often requires detailed knowledge of the interfaces, notably the interfacial energies that determine nucleation barriers and the interfacial mobilities that control growth kinetics—both of which depend sensitively on the the interfacial structures. Beyond their role in transformation kinetics, interfacial structures and the accompanying orientation relationships (ORs) and interface orientations (IOs) are microstructural features in their own right and directly influence bulk properties. Based on extensive studies of diverse alloy systems, we have formulated a unified framework that rationalises the preferred interfaces and their reproducible ORs produced by phase transformations, by employing preferred interfacial structures of two hierarchical levels. At the fine (atomic) level, the interface adopts a low-energy, periodically matched configuration that minimises the nucleation barrier. Such matching is possible only for specific intrinsic ORs and IOs, thereby imposing the geometric constraints. The structures of the coarse level are characterized by singular interfacial defects. Their development, preferred under given phase transformation conditions, allows the OR and IO to deviate within certain limits from the intrinsic values. This talk will present general methods for correlating ORs and IOs with interfacial structures at both levels and will illustrate the approach with examples from several material systems [more]

The importance of different length scales in materials science is well-recognized and subject of intense interdisciplinary research efforts. In these developments, multiscale modelling approaches take a key role as these enable the prediction of the effective material response based on detailed microstructure representations. Against this background, we focus on a scale-bridging understanding of macroscale material interfaces and on the influence of microscale interfaces on the effective properties of continua. We make use of classic energy-based homogenisation approaches, extend these to material interfaces, and demonstrate the usefulness of the proposed generalised multiscale formulations by comparison with experimental data. [more]

Recent studies have shown that the passage of an electric current pulse may both propagate [1,2] and close a crack and heal a metallic material [3]. Specifically, experiments on thin Al foils containing edge cracks have proved that the self-induced electromagnetic forces, spontaneously generated upon passage of an electric current across a crack in a sample, alone could cause crack propagation without melting of the crack tip [1]. The critical current density required for crack propagation reduces in the presence of an external magnetic field [4] as well as mechanical load [5]. On the other hand, if an electric current pulse of large pulse width is passed through an electrically and thermally resistive material, such as stainless steel, containing a short crack, the crack may completely close, and the material can heal through the solid-state diffusion bonding process [3]. Here, we discuss the reasons behind crack propagation upon application of electric current and then explore the mechanics as well as microstructural attributes responsible for a transition from flaw propagation to flaw healing upon passage of an electric current pulse. Furthermore, the recovery of the mechanical properties of the material upon electric current-induced healing will also be discussed. [more]

Defects and Grain boundaries have a remarkable effect on the thermal and electrical transport properties of polycrystalline materials but are often ignored by prevailing physical theories. The concentration of point defects can be altered with phase boundary mapping considering the defect thermodynamics. Thus, the properties can be engineered with careful processing control. Grain boundaries and interfaces can adversely alter the thermal and electrical properties of Power Electronics, Solar Cells, Batteries, Thermoelectrics and permanent magnets such as interfacial electrical and thermal resistance (Kapitza resistance). Interfacial thermal resistance limits the performance of power electronics because of overheating. New scanning thermal reflectance techniques can image the thermal resistance of interfaces and boundaries directly. The Thermal conductivity suppression at grain boundaries can even be imaged showing that different grain boundaries can have very different thermal resistances with high energy grain boundaries having more resistance and low energy boundaries having lower thermal resistance. Interfaces and grain boundaries are 2-dimensional thermodynamic phases (complexions) that have distinct energy, composition and properties that can be rigorously described using the Gibbs excess formalism. The common thermodynamic quantities of temperature and chemical potential connects the complexions to the 3-D phases allowing a phase boundary mapping of grain boundary and interface properties similar to that for point defects. [more]