Dynamical Diffraction Research Articles

Insights into the age and genesis of the clay dunes in the Suhongtu Basin, Alashan Plateau, China

Clay dunes are characterized by high content of silt and clay and they are both a unique aeolian landform and an important paleoenvironmental archive attesting to changing climatic and hydrological conditions. Although clay dunes have been identified on several continents, they have attracted relatively little research attention. Numerous clay dunes are developed in the Suhongtu (SHT) Basin, Alashan Plateau, China. However, their genesis, age, and process of evolution are unknown. In this study we measured the grain size of various clay dune samples using dynamic image analysis (DIA) and laser diffraction analysis (LDA). Comparison of the results obtained by the two methods revealed significant differences between them: the grain size of clay dune samples obtained by DIA have a unimodal distribution (with a mode at ~200–400 μm), and the grain-size composition is dominated by medium sand; while the results obtained using LDA show a bimodal distribution (with modes at ~4 and 200–400 μm), and the grain-size composition consists mainly of clay and silt. This indicates that the clay dunes in the SHT Basin are formed by wind transport and accumulation in the form of the mixing of sand-sized aggregates of clay-silt with quartz sand grains. The morphology, mobility, and sedimentary structures of the clay dunes in the SHT Basin differ substantially from those of the well-studied clay dunes in Australia and North America, which can be mainly attributed to the relatively low clay content, abundant sand source and extremely arid conditions. During field investigations we studied seven stratigraphic sections, comprising multiple aeolian clay dune and lacustrine units, with age control provided by optically stimulated luminescence (OSL) and AMS 14C dating. Lacustrine sediments in the basal parts of sections yielded OSL age between 7.84 ± 0.71 ka and 6.33 ± 0.84 ka, suggesting that the SHT Basin was occupied by a lake during 7.8–6.3 ka when the precipitation was relatively high and the climate was humid. The oldest clay dune deposit, with an AMS 14C age of 1.27 cal kyr B.P, probably represents the onset of the modern clay dune landscape in the SHT Basin. Most of the clay dune deposits yielded OSL ages between 0.50 ± 0.04 ka and 0.18 ± 0.05 ka, indicating aeolian reactivation in the past ~500 years.

Dynamic Surface Wrinkles for In Situ Light-Driven Dynamic Gratings.

Dynamic diffraction gratings (DDGs) are considered as one of the most promising technologies for application in smart optical devices because of their in situ dynamic regulation of light propagation on demand; however, it is still a challenge to fabricate dynamic periodic micro/nanostructures due to limited materials and processes. Here, a facile and feasible strategy to construct a near-infrared (NIR) radiation-driven DDG is developed based on a double-sided surface pattern, which is fabricated by dynamic wrinkles and/or soft-imprinted static wrinkles. Poly(dimethylsiloxane) (PDMS) containing carbon nanotubes (CNTs) serves as the substrate, and wrinkles are formed on both sides. The resulting double-sided wrinkle pattern can be used as a DDG to generate various adjustable two-dimensional (2D) diffraction patterns driven by NIR light. Furthermore, with various combinations of wrinkles, we demonstrated a single-sided responsive DDG and a double-sided responsive DDG to realize the evolution of diffraction patterns from 2D to one-dimensional (1D) and 2D to zero-dimensional (0D), respectively. The results provide an alternative for DDGs that will have wide applications in smart display, sensing, and imaging systems.

Two-dimensional recurrence relations and Takagi–Taupin equations. I. Dynamical X-ray diffraction by a perfect crystal

The dynamical diffraction of spatially restricted X-ray beams in a thick perfect crystal is studied using two-dimensional recurrence relations and the Takagi–Taupin (T-T) equations. It is shown that the two-dimensional recurrence relations are transformed into T-T equations when passing from a crystal with an array of discrete lattice planes to a model of continuous periodic electron density. The results of calculations of the X-ray diffraction field inside the crystal and the angular distribution of the scattering intensity in reciprocal space based on these two approaches are presented. It is shown that, when using the two-dimensional recurrence relations and T-T equations, the calculated contours of reciprocal-space maps and their qx sections are similar to each other, and the qz sections completely coincide.

Volume imaging by tracking sparse topological features in electron micrograph tilt series

The sensitive coherent interference of electron waves arising from a specimen is useful for revealing subtle structural information in electron micrographs, which can be important for minimising dose and for rapid imaging. In general, dynamical diffraction is expected due to the useful strong interactions of electrons with matter, which can create phase contrast that violates the requisite Radon projection assumption for tomography. It is for these reasons that incoherent imaging modalities such as high angle annular dark field have been favoured to date in electron tomography of crystalline specimens, to access a monotonic relationship between specimen thickness and micrograph intensity. Here we use a geometric approach to track topological features that are robust to perturbation of the imaging conditions, to enable 3D reconstructions from electron microscope tilt series under imaging conditions that violate the Radon projection assumption, with an emphasis on phase contrast. Invoking a sparsity assumption, we demonstrate that topological features can be reliably tracked in 3D using a differential geometric form of stereoscopy, to circumvent departures from the projection approximation and reduce noise by effecting segmentation of interest points from the outset. We demonstrate this approach on a variety of different specimen and data types, from polyhedral nanoparticles, to steel dislocation networks, cryo-EM cellular structures and 3D diffuse diffraction of a relaxor ferroelectric.

Development of holmium doped eutectic Sn-Ag lead-free solder for electronic packaging

PurposeThis study aims to summarize the effects of minor addition of Ho REE on the structure, mechanical strength and thermal stability of binary Sn- Ag solder alloys for high-performance applications.Design/methodology/approachThis study investigates the effect of a small amount of holmium addition on the microstructure, thermal stability, mechanical behaviour and wettability of environmentally friendly eutectic melt-spun process Sn – Ag solder alloys. Dynamic resonance technique, X-ray diffraction (XRD) and scanning electron microscopy were carried to study stiffness, identification of the phases and the morphology features of the solder. Structure and microstructure analysis indicated that presence of rhombohedral ß-Sn phase in addition to orthorhombic IMC Ag3Sn phase dispersed in Sn-matrix. Also, the results showed that Ho rare earth addition at a small trace amount into Sn-Ag system reduces and improves the particle size of both rhombohedral ß-Sn and orthorhombic IMC Ag3Sn based on the adsorption effect of the active RE element. The adsorption of Ho at grain boundaries resulted in Ag3Sn more uniform needle-like which is distributed in the ß-Sn matrix. The fine and uniform microstructure leads to improvement of mechanical strength. The microstructure refinement is due to the high surface free energy of IMC Ag3Sn grains, and it prevents the dislocation slipping. This maybe enhance the micro-hardness and micro-creep hence delays the breaking point of the solder. Ho (RE) trace addition could enhance the melting temperature and contact angle up to 215°C and 31°, Respectively, compared with plain solder. All results showed that Ho trace addition element has an effective method to enhance new solder joints.FindingsEffect of rare earth element Ho particles on the microstructure and mechanical behavior of eutectic Sn-3.5Ag solder alloy was studied. Some important conclusions are summarized in the following: microstructure investigations revealed that the addition of Ho particles to eutectic Sn-3.5Ag inhibited in reducing and refines the crystallite size as well as the Ag3Sn IMC which reinforced the strength of plain solder alloy. The mechanical properties values such as Young’s modulus, Vickers microhardness of Sn-3.5Ag solder alloy can be significantly improved by adding a trace amount of Ho particles compared with plain solder due to the existence of finer and higher volume fraction of Ag3SnIMC. These variations can be understood by considering the plastic deformation. The strengthening mechanism of the Sn-3.5Ag-Ho solder alloy could be explained in terms of Ho harden particles and finer IMC, which are distributed within eutectic regions because they act as pinning centres which inhibited the mobility of dislocation that concentrated around the grain boundaries. The results show that the best creep resistance is obtained when the addition of Ho 0.5 is compared to plain solder. The addition of Ho on Sn-3.5Ag lead-free solder alloy decreases the melting temperature to few degrees.Originality/valueDevelopment of holmium-doped eutectic Sn-Ag lead-free solder for electronic packaging.

Generalizing the quantum information model for dynamic diffraction

The development of novel neutron optics devices that rely on perfect crystals and nano-scale features are ushering a new generation of neutron science experiments, from fundamental physics to material characterization of emerging quantum materials. However, the standard theory of dynamical diffraction (DD) that analyzes neutron propagation through perfect crystals does not consider complex geometries, deformations, and/or imperfections which are now becoming a relevant systematic effect in high precision interferometric experiments. In this work, we expand upon a quantum information (QI) model of DD that is based on propagating a particle through a lattice of unitary quantum gates. We show that the model output is mathematically equivalent to the spherical wave solution of the Takagi-Taupin equations when in the appropriate limit, and that the model can be extended to the Bragg as well as the Laue-Bragg geometry where it is consistent with experimental data. The presented results demonstrate the universality of the QI model and its potential for modeling scenarios that are beyond the scope of the standard theory of DD.

Low Thermal Conductivity in Heteroanionic Materials with Layers of Homoleptic Polyhedra.

Although BiAgOSe, an analogue of a well-studied thermoelectric material BiCuOSe, is thermodynamically stable, its synthesis is complicated by the low driving force of formation from the stable binary and ternary intermediates. Here we have developed a "subtraction strategy" to suppress byproducts and produce pure phase BiAgOSe using hydrothermal methods. Electronic structure calculations and optical characterization show that BiAgOSe is an indirect bandgap semiconductor with a bandgap of 0.95 eV. The prepared sample exhibits lower lattice thermal conductivities (0.61 W·m-1·K-1 at room temperature and 0.35 W·m-1·K-1 at 650 K) than BiCuOSe. Lattice dynamical simulations and variable temperature diffraction measurements demonstrate that the low lattice thermal conductivity arises from both the low sound velocity and high phonon-phonon scattering rates in BiAgOSe. These in turn result primarily from the soft Ag-Se bonds in the edge-sharing AgSe4 tetrahedra and large sublattice mismatch between the quasi-two-dimensional [Bi2O2]2+ and [Ag2Se2]2- layers. These results highlight the advantages of manipulating the chemistry of homoleptic polyhedra in heteroanionic compounds for electronic structure and phonon transport control.

Performance of a cryo-cooled crystal monochromator illuminated by hard X-rays with MHz repetition rate at the European X-ray Free-Electron Laser.

Due to the high intensity and MHz repetition rate of photon pulses generated by the European X-ray Free-Electron Laser, the heat load on silicon crystal monochromators can become large and prevent ideal transmission in Bragg diffraction geometry due to crystal deformation. Here, we present experimental data illustrating how heat load affects the performance of a cryogenically cooled monochromator under such conditions. The measurements are in good agreement with a depth-uniform model of X-ray dynamical diffraction taking beam absorption and heat deformation of the crystals into account.

Low-Dose Electron Crystallography: Structure Solution and Refinement

There is a wealth of materials that are beam sensitive and only exist in nanometric crystals, because the growth of bigger crystals is either impossible or so complicated that it is not reasonable to spend enough time and resources to grow big crystals before knowing their potential for research or applications. This difficulty is encountered in minerals, zeolites, metal-organic frameworks or molecular crystals, including pharmaceuticals and biological crystals. In order to study these crystals a structure determination method for beam sensitive crystals of nanometric size is needed. The nanometric size makes them destined for electron diffraction, since electrons interact much more strongly with matter than X-rays or neutrons. In addition, for the same amount of beam damage, electron diffraction yields more information than X-rays. The recently developed low-dose electron diffraction tomography (LD-EDT) not only combines the advantages inherent in electron diffraction, but is also optimized for minimizing the electron dose used for the data collection. The data quality is high, allowing not only the solution of complex unknown structures, but also their refinement taking into account the dynamical diffraction effects. Here we present several examples of crystals solved and refined by this method. The range of the crystals presented includes two synthetic oxides, Sr5CuGe9O24 and (Na2/3Mn1/3)3Ge5O12, a natural mineral (bulachite), and a metal organic framework (Mn-formiate). The dynamical refinement can be successfully performed on data sets that needed less than 0.1 e−/Å2 for the entire data set.

Microstructural modifications induced in Si+-implanted yttria-stabilised zirconia: a combined RBS-C, XRD and Raman investigation.

The structural differences in (100)-, (110)- and (111)-oriented cubic yttria-stabilised zirconia (YSZ) single crystals after implantation with 2 MeV Si+ ions at the fluences of 5 × 1015, 1 × 1016 and 5 × 1016 cm-2 were studied using Rutherford backscattering spectrometry in the channelling mode (RBS-C), X-ray diffraction (XRD) and Raman spectroscopy. The RBS-C results show that the damage accumulation in the 〈110〉 direction exhibits a lower level of disorder (<0.3) than the other orientations (<0.6) and it seems that the (110) crystallographic orientation is the most resistant to radiation damage. The experimental results from the RBS measurement were compared with the results from the XRD measurements. The XRD data were analysed using the standard two-beam dynamical X-ray diffraction theory and the pure isotropic strain was deduced from the fit for the fluence of 5 × 1015 cm-2. It was shown that the maximum value of the isotropic strain does not depend on the surface orientation. The increase in signal intensity at ∼689 cm-1 is probably related to an increase in implantation defects such as oxygen vacancies.

Facile synthesis of iron titanate/nitrogen-doped graphene on Ni foam as a binder-free electrocatalyst for oxygen evolution reaction

• A three-dimensional Fe 2 TiO 5 /nitrogen-doped graphene nanocomposite is prepared using a simple, cheap and fast chemical bath deposition method. • Structural and physical characterizations of the prepared electrocatalyst are performed by different analysis methods. • The fabricated binder-free electrode, by coating the prepared composite on nickel foam, is applied for studying the oxygen evolution reaction. • The prepared electrode showed high electrocatalytic efficiency for oxygen evolution reaction in alkaline medium. • The electrode provided an overpotential of 264.15 mV at 10 mA cm −2 and the Tafel slope is 35 (mV/dec) and also showed long-term stability in alkaline media. Given the growing need for renewable energy and related technologies, researches have shifted to develop low-cost, stable, high-efficiency electrocatalysts in clean energy generation reactions such as water electrolysis. In the present paper, a three-dimensional Fe 2 TiO 5 /nitrogen-doped graphene (3D FTO/NG) nanocomposite is prepared using a simple, cheap and fast method, called chemical bath deposition (CBD). Structural and physical characterizations of the prepared electrocatalysts are performed by different methods such as Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray spectroscopy (EDX), Fourier Transform InfraRed spectra (FT-IR), Dynamic Light Scattering (DLS), X-ray Diffraction (XRD), Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The fabricated binder-free 3D FTO/NG, 3D NG and 3D G on nickel foam (NF) electrodes, were applied to study oxygen evolution reaction (OER) in alkaline medium. Among these electrodes, the 3D FTO/NG electrocatalyst, has an overpotential of 264.15 mV at 10 mA cm −2 and its Tafel slope was 35 (mV/dec). Its long-term stability and excellent performance are due to the simultaneous effect of nitrogen doping and presence of metal oxide nanoparticles, which helped to increase the number of active sites for reaction, adsorption of hydroxide ions and electrode conductivity.

Effective mechanism of BaO on the structure and fluid behavior of CaO-SiO2-B2O3-based melts

The influence of BaO contents on structure and fluid behavior of fluorine-free CaO-SiO2-B2O3 based melts were examined using molecular dynamic (MD) simulation, rotary viscometer, X-ray diffraction and Fourier transform infrared spectroscopy. The FTIR results matched well with the MD simulation results that with the addition of BaO contents in CaO-SiO2-B2O3 based melts, more cations were provided to balance the negative charge of [BO4]5– tetrahedrons, leading to the structures of Si-O and B-O were more aggregated and the adjacent structural units were more closely connected, which made the structure complex, so the viscosity of mold fluxes at high temperature in the basicity range 1.15–1.25 was intensify. Meanwhile, when BaO replaced CaO under distinctive basic conditions, the viscous activity of fluorine-free mold flux was decreasing generally, showing that as the temperature was decreased, the tendency of slag to converge into complex network structural units was also decreasing, which states the improvement of lubrication capacity of the slag during cooling process.

X-ray focusing by bent crystals: focal positions as predicted by the crystal lens equation and the dynamical diffraction theory.

The location of the beam focus when monochromatic X-ray radiation is diffracted by a thin bent crystal is predicted by the `crystal lens equation'. This equation is derived in a general form valid for Bragg and Laue geometries. It has little utility for diffraction in Laue geometry. The focusing effect in the Laue symmetrical case is discussed using concepts of dynamical theory and an extension of the lens equation is proposed. The existence of polychromatic focusing is considered and the feasibility of matching the polychromatic and monochromatic focal positions is discussed.

Electron Microscopy of Nanoporous Crystals

ConspectusNanoporous crystals, such as silica mesoporous crystals (SMCs), zeolites, metal–organic frameworks (MOFs) and covalent organic frameworks (COFs), usually have unique geometrical features of periodically arranged pores from micro-, meso- to macro-scale. They have great potential to be structurally designed toward novel materials for various applications, such as storage, separation, and catalysis. In addition to the synthesis and applications of these materials, the structural analysis of nanoporous crystals is also critical for obtaining novel materials and unravelling their structure–property relationships. The crystal structure determines the pore size and connectivity of cages/channels, which are closely related to the performance of these materials in adsorption and catalysis. However, there are significant challenges in structural analysis due to small crystal size, electron-beam sensitivity, and local defects. Due to the strong interaction between electrons and matter, electron microscopy (EM) can provide rich structural information, which at the same time can also cause structural damage to samples. As early as 1960s, EM had been used to directly observe the lattice fringes of zeolites. Subsequently, the structures of many nanoporous crystals were solved and structural details such as defects, intergrowths, and surface structures were revealed by exploiting EM during the past decades. With the development of three-dimensional electron diffraction (3D ED) and low-dose high-resolution electron microscopy imaging, these approaches become more routine for solving the structure of nanocrystals and for revealing the local structural details. In this Account, we present our previous work on EM studies of several typical nanoporous materials, including SMCs, zeolites, MOFs, the TiO2@MIL-101 composite, and COFs. Various methods and strategies were developed and applied to different materials based on the characteristics of their structures. For example, 3D electrostatic potential maps of SMCs can be reconstructed by Fourier synthesis of crystal structure factors obtained from high-resolution TEM images, leading to the discovery of many 3D mesostructures. New zeolites/MOFs/COFs structures, which were not previously solved due to their structural complexity and small crystal size, have been determined using 3D ED data from nanosized crystals or using a combination of electron diffraction and high-resolution imaging. In addition, EM methods for determining the handedness of nanocrystals have also been developed and successfully applied to SMCs and STW zeolite based on high-resolution EM imaging or dynamical electron diffraction. Recently, a new strategy involving a combination of 3D ED and cryogenic protocol was proposed to study the structure, dynamics, and the host–guest interactions in a COF material. The direct-space strategy for structure solution, implemented using a genetic algorithm, was also demonstrated to be a successful approach for solving structures from low-resolution 3D ED data. By now, EM has become one of the most widely used methods in the study of nanoporous materials. We hope this Account will promote further developments of EM and stimulate the design and synthesis of new functional nanoporous materials.

Photoinduced anisotropic lattice dynamic response and domain formation in thermoelectric SnSe

Identifying and understanding the mechanisms behind strong phonon–phonon scattering in condensed matter systems is critical to maximizing the efficiency of thermoelectric devices. To date, the leading method to address this has been to meticulously survey the full phonon dispersion of the material in order to isolate modes with anomalously large linewidth and temperature-dependence. Here we combine quantitative MeV ultrafast electron diffraction (UED) analysis with Monte Carlo based dynamic diffraction simulation and first-principles calculations to directly unveil the soft, anharmonic lattice distortions of model thermoelectric material SnSe. A small single-crystal sample is photoexcited with ultrafast optical pulses and the soft, anharmonic lattice distortions are isolated using MeV-UED as those associated with long relaxation time and large displacements. We reveal that these modes have interlayer shear strain character, induced mainly by c-axis atomic displacements, resulting in domain formation in the transient state. These findings provide an innovative approach to identify mechanisms for ultralow and anisotropic thermal conductivity and a promising route to optimizing thermoelectric devices.

Dynamical diffraction of high-energy electrons investigated by focal series momentum-resolved scanning transmission electron microscopy at atomic resolution

We report a study of scattering dynamics in crystals employing momentum-resolved scanning transmission electron microscopy under varying illumination conditions. As we perform successive changes of the probe focus, multiple real-space signals are obtained in dependence of the shape of the incident electron wave. With support from extensive simulations, each signal is shown to be characterised by an optimum focus for which the contrast is maximum and which differs among different signals. For instance, a systematic focus mismatch is found between images formed by high-angle scattering, being sensitive to thickness and chemical composition, and the first moment in diffraction space, being sensitive to electric fields. It follows that a single recording at one specific probe focus is usually insufficient to characterise materials comprehensively. Most importantly, we demonstrate in experiment and simulation that the second moment μ20+μ02=〈p2〉 of the diffracted intensity exhibits a contrast maximum when the electron probe is focused at the top and bottom faces of the specimen, making the presented concept attractive for measuring local topography. Given the versatility of 〈p2〉, we furthermore present a detailed study of its large-angle convergence both analytically using the Mott scattering approach, and by dynamical simulations using the multislice algorithm including thermal diffuse scattering. Both approaches are in very good agreement and yield logarithmic divergence with increasing scattering angle.

A simultaneous strategy for the preparation of acetylation modified cellulose nanofiber/polypropylene composites

In this study, a simultaneous method with nano-fibrillation of acetylation modified fibers (A-cellulose) and preparation of cellulose nanofiber (CNF)/apolar polymer composites are proposed. The A-cellulose and isotactic polypropylene (iPP) were initially mixed and then melt-compounding in a twin-screw extruder. Due to the reduction of hydrogen bonding force inside A-cellulose and the high shear force provided by the extruder, acetylated cellulose nanofiber (A-CNF) distributed with the state of a three-dimensional network in PP composites (ACPP) were successful prepared. The scanning electron microscopy (SEM) images of A-CNF, dynamic mechanical analysis (DMA) and X-ray diffraction (XRD) results of ACPP showed that the A-CNF had good interface compatibility with PP matrix, and had the effects of inducing PP crystallization, decreasing crystal size and increasing the ratio of γ crystals in composites, which could improve the mechanical and thermodynamic properties of composites.

Imaging Ultrafast Dynamical Diffraction Wave Fronts in Strained Si with Coherent X Rays.

Dynamical diffraction effects in thin single crystals produce highly monochromatic parallel x-ray beams with a mutual separation of a few microns and a time delay of a few femtoseconds-the so-called echoes. This ultrafast diffraction effect is used at X-Ray Free Electron Lasers in self-seeding schemes to improve beam monochromaticity. Here, we present a coherent x-ray imaging measurement of echoes from Si crystals and demonstrate that a small surface strain can be used to tune their temporal delay. These results represent a first step toward the ambitious goal of strain tailoring new x-ray optics and, conversely, open up the possibility of using ultrafast dynamical diffraction effects to study strain in materials.

Calculated performance of multilayer Laue lens based on actual layer thickness and coupled wave theory

The multilayer Laue lens (MLL) is a promising optical element with large numerical aperture and aspect ratio in synchrotron radiation facility to focus hard x-ray to 1 nm with ideal structure. We use a new method of combining actual film thickness and the coupled wave theory to calculate focusing performance. Here, a 17.2-μm-MLL with a focal spot size of 17 nm at 10 keV is designed and fabricated by dynamical diffraction theory and direct current magnetron sputtering technology. Based on a new rate calibration and symbol layer insertion method, we calculate d-spacing of multilayer instead of individual layer thickness and change the order of two layers as a symbol so as not to damage zone plate law. The scanning electron microscope image is smoothed and binary transformed to measure the actual thickness of each layer. The full-width at half-maximum of focus spot is 18 nm, which is close to the theoretical result of 17 nm.

New developments including X-ray standing waves in the dynamical Bragg diffraction program of X-ray Server.

X-ray Server (https://x-server.gmca.aps.anl.gov) is a collection of programs for online modelling of X-ray diffraction and scattering. The dynamical diffraction program is the second most popular Server program, contributing 34% of total Server usage. It models dynamical X-ray diffraction from strained crystals and multilayers for any Bragg-case geometry including grazing incidence and exit. This paper reports on a revision of equations used by the program, which yields ten times faster calculations in most use cases, on implementing calculations of X-ray standing waves and on adding new options for modelling diffraction from monolayers.