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Laboratory model for radio star scintillation and other diffraction phenomena by thin weak random phase changing screen including earth atmosphere or solar wind
Spontaneous Hall conductivity has recently been reported in the triangular lattice antiferromagnet Co 1/3 TaS 2 under a zero magnetic field. This phenomenon originates from the distinctive noncoplanar triple-Q magnetic ground state, possessing uniform real-space Berry curvature characterized by scalar spin chirality. We investigated the physical properties of Co 1/3 TaS 2 by judiciously controlling the composition, revealing a drastic change in its bulk properties, even by slight variations in cobalt composition, despite the same crystal structure. For 0.299≤x≤0.325, Co x TaS 2 keeps all the characteristics of the ground state consistent with the previous studies—two antiferromagnetic phase transitions at T N1 and T N2 ( N1 ), a large spontaneous Hall conductivity [σ xy (H=0)], and a weak ferromagnetic moment along the c axis. However, samples with x≥0.330 exhibit distinct bulk properties, including the absence of both σ xy (H=0) and the weak ferromagnetic moment. Our neutron diffraction data reveal that Co x TaS 2 with x≥0.330 develops coplanar helical magnetic order with q m1 =(1/3, 0, 0). This is entirely different from what has been seen in x≤0.325, explaining the observed composition dependence.
The microstructure and 650 °C tensile properties of a compositionally graded IN718-René41 (718-R41) superalloy fabricated by laser blown-powder directed energy deposition (DED-LB/M) are investigated to understand structure–property relationships and baseline tensile properties. Digital Image Correlation (DIC), in situ neutron diffraction, and conventional characterization techniques are performed to study the as-built and heat-treated states. The applied heat treatment generates static recrystallization and equiaxed grains in 718-rich compositions, while R41-rich compositions remain partially or un-recrystallized possibly influenced by a higher MC carbide fraction (>0.5%). The yield strengths of the 718 and R41 sections in the heat-treated state are comparable to wrought forms but the graded compositions show weakness due to unoptimized heat treatment. Diffraction elastic constants first decrease and then increase along the 718-R41 composition gradient, while a small difference is observed between the as-built and heat-treated states and γ, γ′ phases. Overall, the compositionally graded region shows a smooth transition in the elastic properties. Grain-level load transfer from the (220) to (200) grains shows compositional dependence, and qualitatively agrees with DIC-measured macroscopic yield strength. Within the (200) grains, the γ/γ′ phases deform elastically until the γ phase yields and afterwards, the γ′ phase takes load from the γ phase.
Nonlinear optical response is a fingerprint of various physicochemical properties of materials related to symmetry, including crystallography, interfacial configuration, and carrier dynamics. However, the intrinsically weak nonlinear optical susceptibility and the diffraction limit of far-field optics restrict probing deep-subwavelength-scale nonlinear optics with measurable signal-to-noise ratio. Here, we propose an alternative approach toward efficient second harmonic generation (SHG) nanoscopy for SHG-active sample (zinc oxide nanowire; ZnO NW) using an SHG-active plasmonic nanotip. Our full-wave simulation suggests that the experimentally observed high near-field SHG contrast is possible when the nonlinear response of ZnO NW is enhanced and/or that of the tip is suppressed. Here, this result suggests possible evidence of quantum mechanical nonlinear energy transfer between the tip and the sample, modifying the nonlinear optical susceptibility. Further, this process probes the nanoscale corrosion of ZnO NW, demonstrating potential use in studying various physicochemical phenomena in nanoscale resolution.
Single-crystalline membranes of functional materials enable the tuning of properties via extreme strain states; however, conventional routes for producing membranes require the use of sacrificial layers and chemical etchants, which can both damage the membrane and limit the ability to make them ultrathin. Here we demonstrate the epitaxial growth of the cubic Heusler compound GdPtSb on graphene-terminated Al 2 O 3 substrates. Despite the presence of the graphene interlayer, the Heusler films have epitaxial registry to the underlying sapphire, as revealed by x-ray diffraction, reflection high energy electron diffraction, and transmission electron microscopy. The weak Van der Waals interactions of graphene enable mechanical exfoliation to yield free-standing GdPtSb membranes, which form ripples when transferred to a flexible polymer handle. Whereas unstrained GdPtSb is antiferromagnetic, measurements on rippled membranes show a spontaneous magnetic moment at room temperature, with a saturation magnetization of 5.2 bohr magneton per Gd. First-principles calculations show that the coupling to homogeneous strain is too small to induce ferromagnetism, suggesting a dominant role for strain gradients. Our membranes provide a novel platform for tuning the magnetic properties of intermetallic compounds via strain (piezomagnetism and magnetostriction) and strain gradients (flexomagnetism).
We present an approach for simulating x-ray nanobeam Bragg coherent diffraction patterns based on the Takagi-Taupin equations. Compared to conventional methods, the current approach can be universally applied to any weakly strained system including semi-infinite crystals that diffract dynamically. It addresses issues such as the curved wave front and redivergence of the focused incident beam. In conclusion, we show excellent agreement with experimental data for a strained La 0.7 Sr 0.3 MnO 3 thin film on a SrTiO 3 substrate and a path to extracting physical information using automatic differentiation.
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.
Simulations of photochemical reaction dynamics have been a challenge to the theoretical chemistry community for some time. In an effort to determine the predictive character of current approaches, we predict the results of an upcoming ultrafast diffraction experiment on the photodynamics of cyclobutanone after excitation to the lowest lying Rydberg state (S 2 ). A picosecond of nonadiabatic dynamics is described with ab initio multiple spawning. Herein we use both time dependent density functional theory (TDDFT) and equation-of-motion coupled cluster singles and doubles (EOM-CCSD) theory for the underlying electronic structure theory. We find that the lifetime of the S 2 state is more than a picosecond (with both TDDFT and EOM-CCSD). The predicted ultrafast electron diffraction spectrum exhibits numerous structural features, but weak time dependence over the course of the simulations.
The surface magnetization of Fe 3 GeTe 2 was examined by low-energy electron microscopy (LEEM) using an off-normal incidence electron beam. We found that the 180o domain walls are of Bloch type. Temperature-dependent LEEM measurements yield a surface magnetization with a surface critical exponent β1 = 0.79±0.02. This result is consistent with surface magnetism in the 3D semi-infinite Heisenberg (β1 = 0.84±0.01) or Ising (β1 = 0.78±0.02) models, which is distinctly different from the bulk exponent (β = 0.34±0.07). Further, the measurements reveal the power of LEEM with a tilted beam to determine magnetic domain structure in quantum materials, without need for the use of spin-polarized electrons. Single crystal diffraction measurements reveal inversion symmetry-breaking weak peaks and yield space group P-6m2. This Fe site defect-derived loss of inversion symmetry enables the formation of skyrmions in this Fe 3 GeTe 2 crystal.
Reactive sputtering was used to grow thin films of Sc(x)Ga(1-x)N with scandium concentrations of 20%-70% on quartz substrates at temperatures of 300-675 K. X-ray diffraction (XRD) of the films showed either weak or no structure, suggesting the films are amorphous or microcrystalline. Optical absorption spectra were taken of each sample and the optical band gap was determined. The band gap varied linearly with increasing Ga concentration between 2.0 and 3.5 eV. Ellipsometry was used to confirm the band gap measurements and provide optical constants in the range 250-1200 nm. ScN and GaN have different crystal structures (rocksalt and wurzite, respectively), and thus may form a heterogeneous mixture as opposed to an alloy. Since the XRD data were inconclusive, bilayers of ScN/GaN were grown and optical absorption spectra taken. A fundamental difference in the spectra between the bilayer films and alloy films was seen, suggesting the films are alloys, not heterogeneous mixtures.
A flow-visualizing system with a scanning optical beam offers greater advantages than the conventional approaches. In addition to a higher signal-to-noise ratio and lower source power, the scanning permits visualization of weak phenomena such as the scattering and diffraction of light on shocks. Scanning beam flow-visualization techniques were evaluated at the NASA Lewis Research Center for shock position sensing. In an effort to eliminate moving parts, a spectral scanning technique was invented and demonstrated.
A volume of an additively manufactured 316L stainless steel sample has been tracked during its recrystallization using near-and far-field High Energy Diffraction Microscopy (HEDM) and absorption tomography at Advanced Photon Source beamline 1-ID. A nearfield compatible in situ furnace allows monitoring of Bragg diffraction signals as they evolve out of a weak and diffuse background while the sample temperature is approximate to 1250 degrees C. The sample is rapidly cooled to room temperature after observation of significant signal evolution and ti similar to 0.035 mm(3) is mapped by the near-field method. Four cycles of heat treatment follow the structure from a state of small, isolated grains through impingement of domains to near completion of recyrstallization. Here, the experiment and reconstructions are described, and recrystallized fractions, twin domains, and distributions of grain boundary types are discussed.
PIONEER is a time-of-flight single-crystal neutron diffractometer at the Second Target Station (STS), aiming at providing the world-leading capability to measure tiny crystals (~0.001 mm 3 , i.e., X-ray diffraction size), ultra-thin epitaxial films (~10 nm thicknesses), and weak structural transitions and complex magnetism. The instrument will take advantage of STS source characteristics and utilize advancements in neutron optics to largely reduce the sample-volume requirement for single-crystal neutron diffraction. PIONEER will have a high-flux mode with multiple beam size options to improve the signal-to-background ratio in various sample environments. It will also provide a high Q-resolution mode by limiting beam divergence to study periodically modulated structures with characteristic lengths no less than 100 Å. Furthermore, it supports half-polarized neutron diffraction for investigating complex magnetism and local susceptibility. This report first overviews the proposed science case and the derived requirement. And then, the chosen technical solutions and expected performance will be described.
Ultrafast-optical-pump — structural-probe measurements, including ultrafast electron and x-ray scattering, provide direct experimental access to the fundamental timescales of atomic motion, and are thus foundational techniques for studying matter out of equilibrium. High-performance detectors are needed in scattering experiments to obtain maximum scientific value from every probe particle. Here we deploy a hybrid pixel array direct electron detector to perform ultrafast electron diffraction experiments on a WSe 2 /MoSe 2 2D heterobilayer, resolving the weak features of diffuse scattering and moiré superlattice structure without saturating the zero order peak. Enabled by the detector’s high frame rate, we show that a chopping technique provides diffraction difference images with signal-to-noise at the shot noise limit. Finally, we demonstrate that a fast detector frame rate coupled with a high repetition rate probe can provide continuous time resolution from femtoseconds to seconds, enabling us to perform a scanning ultrafast electron diffraction experiment that maps thermal transport in WSe 2 /MoSe 2 and resolves distinct diffusion mechanisms in space and time.
We report a size-dependent solute clustering mechanism at grain boundaries in a sputtered ultrafine-grained Ag-Cu alloy, where large Cu clusters form despite weak individual solute-solute interactions. X-ray diffraction confirms limited Cu solubility in the Ag matrix, while scanning transmission electron microscopy reveals Cu clustering at both ordinary GBs and GB junctions. Density functional theory calculations show that 12-atom Cu clusters are energetically preferred, while smaller three-atom clusters are significantly less stable. Additional calculations demonstrate a marked increase in solute-cluster attraction energy with cluster size. As a result, these findings point to a previously unrecognized pathway for grain-boundary solute clustering in immiscible systems, driven by collective solute-cluster interactions, with implications for segregation behavior and stability in nanocrystalline and ultrafine-grained alloys.
Nominally weakly coordinating anions are useful for modulating the solubility and chemical properties of metal complexes, but identification and analysis of the systematics of the interactions of anions with cationic metal complexes has not received the attention it deserves. Here, a chemical informatics approach is demonstrated for identifying and quantitatively analyzing the ways that the bis(trifluoromethylsulfonyl)imide anion (TFSI) can interact with metal-containing species. An open access computer program (PyCIFTer) was developed to facilitate large-scale structural analysis of TFSI-containing species by utilization of experimental atomic coordinate data from single-crystal X-ray diffraction (XRD) studies obtained from the Cambridge Structural Database (CSD). PyCIFTer establishes a three-dimensional vector space from the raw atomic coordinates, generating acyclic, undirected graphs that are used to rapidly analyze the structural properties (bond lengths and angles) of TFSI in individual structures in sequential/batch fashion. The structures are sorted by PyCIFTer into groups based on pre-set and chemically sensible criteria, affording a comprehensive and systematic view of TFSI structural chemistry. This approach avoids tedious one-at-a-time interrogation of structures, a prospect unreasonable in this case, and many others of contemporary chemical relevance; there were over 1500 structures in the CSD containing TFSI as of November 2024. The results demonstrate that TFSI only rarely binds to cations in the solid state, favoring the formation of species in which TFSI is found in cations’ outer coordination spheres. The prospect of applying PyCIFTer to other moieties is also discussed. PyCIFTer is also schematically compared to the commercial CSD Python application programming interface (API). Taken together, this work demonstrates the usefulness of modular workflows for sequential/batch analysis of structural data from XRD, an approach that appears poised to accelerate the translation of legacy structural results into new chemical insights and hypotheses.
A polymorph of Cu 2 OSeO 3 with the distorted kagome lattice is successfully obtained using the high-pressure synthesis technique (Cu 2 OSeO 3 -HP). The structural analysis using X-ray and neutron powder diffraction suggests that the tetrahedral Cu 2+ clusters [similar to those in Cu 2 OSeO 3 ambient-pressure phase (Cu 2 OSeO 3 -AP)] exist in Cu 2 OSeO 3 -HP but with three symmetry inequivalent sites. No structural change is observed between 1.5 K and the room temperature. The complex magnetic H-T phase diagram is established based on the temperature- and field-dependent magnetization data, indicating two distinct antiferromagnetic phases at low and intermediate temperatures, in addition to the higher-temperature spin-glass-like phase. The low temperature phase is identified by neutron powder diffraction refinements as a canted noncollinear antiferromagnetic order with a weak ferromagnetic component along the b-axis. Size of the refined ordered moment is ≈1.00(4) µ B in Cu 2 OSeO 3 -HP, indicating a large enhancement compared to that of Cu 2 OSeO 3 -AP (≈0.61 µ B ). By applying a uniaxial stress, finite enhancement of weak ferromagnetic component in the noncollinear antiferromagnetic phase in Cu 2 OSeO 3 -HP is observed, which is the clear evidence of the piezomagnetic effect. Interestingly, the sign of the induced magnetization changes on heating from the low-temperature to the intermediate-temperature phases, indicating a novel piezomagnetic switching effect in this compound.
Macromolecular crystallography contributes significantly to understanding diseases and, more importantly, how to treat them by providing atomic resolution 3D structures of proteins. This is achieved by collecting X-ray diffraction images of protein crystals from important biological pathways. Spotfinders are used to detect the presence of crystals with usable data, and the spots from such crystals are the primary data used to solve the relevant structures. Having fast and accurate spot finding is essential, but recent advances in synchrotron beamlines used to generate X-ray diffraction images have brought us to the limits of what the best existing spotfinders can do. This bottleneck must be removed so spotfinder software can keep pace with the X-ray beamline hardware improvements and be able to see the weak or diffuse spots required to solve the most challenging problems encountered when working with diffraction images. In this paper, we first present Bragg Spot Detection (BSD), a large benchmark Bragg spot image dataset that contains 304 images with more than 66 000 spots. We then discuss the open source extensible U-Net-based spotfinder Bragg Spot Finder (BSF), with image pre-processing, a U-Net segmentation backbone, and post-processing that includes artifact removal and watershed segmentation. Finally, we perform experiments on the BSD benchmark and obtain results that are (in terms of accuracy) comparable to or better than those obtained with two popular spotfinder software packages ( Dozor and DIALS ), demonstrating that this is an appropriate framework to support future extensions and improvements.