Dina Sheyfer

Here, we investigate composition fluctuations in the TRUEX organic phase, a chemical system developed for liquid–liquid extraction (LLE) of transuranic elements from acidic aqueous media. This organic phase consists of two amphiphilic extractants, TBP (tributyl phosphate) and CMPO (octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide) dissolved in dodecane. Previous studies of similar LLE systems involving only a single extractant have found critical fluctuations associated with phase separation within the organic phase that are consistent with the 3D Ising universality class. Here we use small-angle X-ray scattering (SAXS) to observe the growth of equilibrium fluctuations as a function of temperature approaching the instability (spinodal). We also use X-ray photon correlation spectroscopy (XPCS) to characterize the dynamics of the fluctuations. Both the statics and dynamics obey scaling laws from the theory of critical fluctuations but with parameters that differ from those expected for binary fluids. Viewing the mesoscale structures in these LLE systems in terms of critical fluctuations provides a general framework for understanding their function.

Complex, multicomponent liquids with hierarchical structure and phase transitions are encountered in many natural and industrial processes, including in chemical separations. One notable example is aggregation and organic phase splitting in liquid-liquid extraction (LLE) of metal ions. While these two phenomena that have long been closely associated, a mechanistic link between mesoscale structure and the capacity-limiting organic phase splitting remains elusive due to complexity of these systems. Here, we combine small-angle X-ray scattering (SAXS), X-ray photon correlation spectroscopy (XPCS), and molecular dynamics simulation to reveal a comprehensive picture of structure at the nano- and mesoscale in these complex solutions. For the representative case of rare earth extraction from an acidic aqueous phase by a malonamide extractant in dodecane, we investigate a wide range of process-relevant extractant and acid concentrations to provide a complete picture of how aggregation depends on composition. We decompose organic phase structure from SAXS into two contributions, which together can capture the scattering at all compositions: composition fluctuations described by the Ornstein-Zernike equation at low wavenumber Q, and nanostructure modeled by a "pre-peak" at intermediate Q. The former contains information about the thermodynamics of demixing, while the latter reflects nanoscopic self-assembly of the extractant and extracted solutes. While fluctuations have typically not been considered in the literature, we find they in fact dominate the total structure for nearly all practical conditions. As only the fluctuations have a strong temperature response, we confirm this attribution with temperature-dependent SAXS measurements, including for extracted europium nitrate complexes. SAXS and XPCS measurements near the critical point find static and dynamic scaling consistent with theory. Overall, this new paradigm for understanding LLE organic phases connects composition, nanoscale, and mesoscale structuring to phase behavior, providing both a comprehensive picture of solution structure and a quantitative link between aggregation and third phase formation.

Dendritic growth is a major cause of battery failure, occurring under diffusion-limited conditions regardless of material crystallinity. We developed an operando visualization setup─complemented by post-mortem analysis using microscopy and synchrotron scattering─to study electrochemical dendrite growth of metals with spatiotemporal resolution. Using Zn electro-crystallization in a series of ZnCl₂ electrolytes as a model system, we found that dendritic growth is most severe in both dilute (0.01–0.5 m) and highly concentrated (10–30 m) systems, as predicted by the dimensionless second Damköhler number, D_a,II = J₀/J_lim. However, we discovered unexpectedly that in highly concentrated electrolytes, dendrites propagate via Continuous Growth (Dendrite Mode I: CG)─initiating from only a few dominant nuclei and propagating anisotropically in one primary direction, with parallel arms suggesting Zn’s six-fold hexagonal lattice symmetry. Advancing along this preferred direction at rates up to ∼0.1 mm s^–1 toward the counter electrode, these dendrites pose a critical challenge, making highly concentrated, water-in-salt electrolytes particularly susceptible to fatal diffusion-limited dendrite growth. We hypothesize that Mode I: CG arises from Zn’s high surface anisotropy, dictated by its low-symmetry hexagonal lattice; once nucleated, Zn crystals preferentially propagate in the ⟨100⟩ direction rather than forming new independent nuclei. In stark contrast, Cu─a high-symmetry cubic crystal─exhibits Dendrite Mode II: IN, characterized by Independent Nucleation throughout growth, with no apparent orientational correlation or dominance by a few dendrites. This finding highlights a hidden role of crystal anisotropy in electrochemical dendrite formation, unaccounted for in classical D_a,II analyses. We further hypothesize that introducing a polymeric “capping” agent that lowers the energy barrier for independent nucleation may shift dendrite growth from Mode I: CG to Mode II: IN. Indeed, we found that the capping agent (e.g., PEG-400) disrupts rapid anisotropic dendritic propagation and promotes numerous smaller structures characteristic of Mode II: IN─surprisingly, without significantly affecting key electrochemical properties such as reaction kinetics J₀ and ionic conductivity σ. The transition from Mode I: CG to Mode II: IN enhances the performance of Zn anodes by a factor of 10 in practical coin cells under fast-charging conditions (50 mA cm^–2 and 5 mAh cm^–2). The results highlight the overlooked role of crystal anisotropy in electrochemical diffusion-limited dendrite growth. Task-specific interventions are required for mitigating low-symmetry metals’ propensity for Mode I: CG, where rapid dendrite advancement occurs, in concentrated electrolytes─such as the emerging water-in-salt systems─under fast-charging conditions.

Traditional Laue diffraction pattern indexing often struggles with noisy data, weak signals, peak overlap and missing reflections, particularly from complex or deformed microstructures. Here, we introduce LaueMatching , a high-throughput indexing algorithm designed to overcome these limitations. LaueMatching utilizes a fundamentally different approach based on direct pattern correlation: experimentally pre-processed images are compared against a comprehensive pre-computed library of simulated diffraction patterns corresponding to a dense grid of possible orientations. This approach bypasses the need for explicit peak identification and fitting, steps that are often a failure point for traditional methods. The algorithm rapidly and robustly indexes multiple crystallographic orientations and crystal systems simultaneously, even from challenging patterns. LaueMatching 's effectiveness and accuracy have been rigorously tested and validated on diverse experimental (Ni, Al, EuAl ₂ O ₄ ) and simulated diffraction patterns, demonstrating high-fidelity orientation refinement. Code to implement this approach on both CPU and GPU resources can be downloaded from https://github.com/AdvancedPhotonSource/LaueMatching.

Coded apertures, initially developed for x-ray astronomy, are gaining traction as a means of enabling depth-resolved imaging in synchrotron-based diffraction experiments. In this study, we evaluate their application to microscale diffraction, focusing on how design and acquisition parameters influence the ability to reconstruct depth-dependent scattering signals. Through systematic simulations, we investigate the impact of bit size, aperture thickness, scan length, and local pattern characteristics on the accuracy of position and signal recovery. We introduce metrics to quantify reconstruction success and identify trade-offs among design variables. Experimental validation using a synchrotron-based micro-diffraction setup confirms the key trends observed in simulation, demonstrating that a moderate scan length and mask aspect ratio suffice for robust signal recovery, even under noisy conditions. Our findings provide a framework for implementing coded apertures in various diffraction geometries, offering a scalable and sample-motion-free approach to 3D structural characterization, particularly relevant for new synchrotron facilities.

Organic phase aggregation and phase splitting are two important (and connected) phenomena in liquid-liquid extraction of metal ions. Previously, we demonstrated how structure in binary mixtures of extractant and diluent originates from concentration fluctuations associated with the so-called "third-phase formation" liquid-liquid phase instability. For more complex systems, we sought to understand how extracted aqueous components affect these concentration fluctuations. In this study, we use small-angle X-ray scattering and molecular dynamics simulations to investigate organic phase structural changes upon contact with water in a model ternary system of water/alkane/extractant. Critical exponents were determined from scattering with temperature variation and were consistent with mean field values. Then, by controlling the water content in the organic phase through direct dissolution of fixed quantities at constant temperature, we relate the observed increase in the fluctuation length scale to changes to the spinodal temperature of the third-phase formation phase boundary. We find a roughly linear relationship between water concentration and the spinodal temperature and a similar slope in that relationship for different linear alkane diluents. This suggests that the mechanism by which water extraction impacts the organic phase structure is to enhance concentration fluctuations through the introduction of additional polar extractant-water complexes, which increases the spinodal temperature and thereby decreases the reduced temperature, i.e., the distance to the instability. This explanation for how solutes induce aggregation in liquid-liquid extraction organic phases may extend to more complex systems, explaining the large increases in correlation lengths reported under high acid and metal loading.

Dendritic growth is a major cause of battery failure, occurring under diffusion-limited conditions regardless of material crystallinity. We developed an operando visualization setup—complemented by post-mortem analysis using microscopy and synchrotron scattering—to study electrochemical dendrite growth of metals with spatiotemporal resolution. Using Zn electro-crystallization in a series of ZnCl2 electrolytes as a model system, we found that dendritic growth is most severe in both dilute (0.01–0.5 m) and highly concentrated (10–30 m) systems, as predicted by the dimensionless second Damköhler number, D_(a,II)=J_0/J_lim. However, we discovered unexpectedly that in highly concentrated electrolytes, dendrites propagate via Continuous Growth (Dendrite Mode I: CG)—initiating from only a few dominant nuclei and propagating anisotropically in one primary direction, with parallel arms suggesting Zn’s six-fold hexagonal lattice symmetry. Advancing along this preferred direction at rates up to ~0.1 mm s-1 toward the counter electrode, these dendrites pose a critical challenge, making highly concentrated, water-in-salt electrolytes particularly susceptible to fatal diffusion-limited dendrite growth. We hypothesize that Mode I: CG arises from Zn’s high surface anisotropy, dictated by its low-symmetry hexagonal lattice; once nucleated, Zn crystals preferentially propagate in the direction rather than forming new independent nuclei. In stark contrast, Cu—a high-symmetry cubic crystal—exhibits Dendrite Mode II: IN, characterized by Independent Nucleation throughout growth, with no apparent orientational correlation or dominance by a few dendrites. This finding highlights a hidden role of crystal anisotropy in electrochemical dendrite formation, unaccounted for in classical D_(a,II) analyses. We further hypothesize that introducing a polymeric “capping” agent that lowers the energy barrier for independent nucleation may shift dendrite growth from Mode I: CG to Mode II: IN. Indeed, we found that the capping agent (e.g., PEG-400) disrupts rapid anisotropic dendritic propagation and promotes numerous smaller structures characteristic of Mode II: IN—surprisingly, without significantly affecting key electrochemical properties such as reaction kinetics J_0 and ionic conductivity σ. The transition from Mode I: CG to Mode II: IN enhances the performance of Zn anodes by a factor of 10 in practical coin cells under fast-charging conditions (50 mA cm-2 and 5 mAh cm-2). The results highlight the overlooked role of crystal anisotropy in electrochemical diffusion-limited dendrite growth. Task-specific interventions are required for mitigating low-symmetry metals’ propensity for Mode I: CG, where rapid dendrite advancement occurs, in concentrated electrolytes—such as the emerging water-in-salt systems—under fast-charging conditions.

Dark-field X-ray microscopy is a lens-based technique that enables real-space imaging of heterogeneous micro- and meso-scale ordered materials. However, achieving accurate three-dimensional (3D) reconstruction often requires meticulous sample alignment or rastering, requiring complex rotational setups and extended acquisition times. To address these challenges, we introduce a structured illumination technique optimized for 3D imaging of ordered materials at sub-micrometer length scales. Our approach employs a coded aperture to spatially modulate the incident X-ray beam, enabling 3D structural reconstruction from images captured at various aperture positions. Unlike current 3D imaging approaches, which often rely on rotational or rastering methods, our technique uses scanning X-ray silhouettes of the coded aperture for depth resolution along the diffraction axis. This eliminates the need for sample rotation or rastering, resulting in a highly stable and efficient imaging modality. We validated the efficacy of this approach through experimental imaging of an isolated twin domain within a bulk single crystal of an iron pnictide using a dark-field X-ray microscope. This advancement aligns with the enhanced brightness upgrades of modern synchrotron radiation facilities, unlocking new possibilities for high-resolution imaging of ordered materials.

Understanding the microscopic origin of the superior electromechanical response in relaxor ferroelectrics requires knowledge not only of the atomic-scale formation of polar nanodomains (PNDs) but also the rules governing the arrangements and stimulated response of PNDs over longer distances. Using x-ray coherent nanodiffraction, we show the staggered self-assembly of PNDs into unidirectional mesostructures that we refer to as polar laminates in the relaxor ferroelectric 0.68PbMg_1/3Nb_2/3O₃-0.32PbTiO₃(PMN-0.32PT). We reveal the highly heterogeneous electric-field–driven responses of intra- and interlaminate PNDs and establish their correlation with the local strain and the nature of the PND walls. Our observations highlight the critical role of hierarchical lattice organizations on macroscopic material properties and provide guiding principles for the understanding and design of relaxors and a wide range of quantum and functional materials.

Thermal annealing is a widely used strategy to enhance semiconductor device performance. However, the process is complex for multi-material multi-layered semiconductor devices, where thermoelastic stresses from lattice constant and thermal expansion coefficient mismatch may create more defects than those annealed. We propose an alternate low temperature annealing technique, which utilizes the electron wind force (EWF) induced by small duty cycle high density pulsed current. To demonstrate its effectiveness, we intentionally degrade AlGaN/GaN high electron mobility transistors (HEMTs) with accelerated OFF-state stressing to increase ON-resistance ∼182.08% and reduce drain saturation current ∼85.82% of pristine condition at a gate voltage of 0 V. We then performed the EWF annealing to recover the corresponding values back to ∼122.21% and ∼93.10%, respectively. The peak transconductance, degraded to ∼76.58% of pristine at the drain voltage of 3 V, was also recovered back to ∼92.38%. This recovery of previously degraded transport properties is attributed to approximately 80% recovery of carrier mobility, which occurs during EWF annealing. We performed synchrotron differential aperture x-ray microscopy measurements to correlate these annealing effects with the lattice structural changes. We found a reduction of lattice plane spacing of (001) planes and stress within the GaN layer under the gate region after EWF annealing, suggesting a corresponding decrease in defect density. Application of this low-temperature annealing technique for in-operando recovery of degraded electronic devices is discussed.