Electron diffraction in structural chemistry.

These past few years, many new structures have been solved using electron diffraction methods: zone axis precession electron diffraction (PED) and tomography in reciprocal space. Both methods enable to reduce importantly the multiple scattering, so that the reflection intensities can be used for structure determination by direct methods. The ferrite Sr25Fe30O77 belongs to a family of phases whose structures consist of an intergrowth of m perovskite layers with complex rocksalt type layers [1,2]. The compound of interest is the member m = 4 of this family and its structure has been solved by combining both electron diffraction methods cited above. This oxide crystallizes in an orthorhombic system with the sub-cell parameters a ≍ b ≍ 5.4 Å and c ≍ 42 Å in a F type lattice. The structure exhibits modulation along a axis with a modulation vector q = 2/5 a. The commensurate nature of the modulation enables to describe the structure in a supercell with the cell parameters a ≍ 27 Å, b ≍ 5.4 Å and c ≍ 42 Å. PED patterns were recorded in zone axis with a Spinning Star unit using a precession angle of 20. The intensities were extracted with CRISP software and the resulting dataset was then implemented in SIR2008 for structure solution. The tomography data collection, recorded by tilting manually every 0.5 degree from -30 to +30 degrees, was inserted in a "3D Electron Diffraction Tomography" software, which reconstructs the 3D reciprocal space and extracts automatically the reflection intensities. The intensity file was then used on SIR2008 for structure determination. In order to confirm and refine the structural model, a powder X-ray diffraction pattern was performed on a laboratory diffractometer with Cu Ka1 radiation. Cell parameters were refined with the WinPlotr and FullProf Softwares using both LeBail and Rietveld methods [3]. The structural model obtained with electron diffraction data was tried and confirmed as the correct structure by the Rietveld refinements.

Convergent beam electron diffraction (CBED) at vertical grain boundaries (parallel to the electron beam) can be applied to determine the symmetry of bicrystals. It can also be used to investigate the structure of the boundary region itself when subnanometre probe sizes are employed. In this paper it is shown that (sub)nanometre-probe CBED patterns are largely influenced by the electron-beam geometry. In particular, simulations of coherent CBED patterns based on the multislice algorithm show that the CBED pattern of an edge-on interface depends on the defocus distance between the probe position and the specimen midplane, the probe size and the beam-convergence angle. The pattern symmetry may be lower than the theoretically predicted symmetry in case of large spherical aberration. This effect increases with smaller accelerating voltages. An increase in the beam-convergence angle also increases the possibility of a non-optimum symmetry due to spherical aberration of a coherent probe. Thus, for the determination of an interface structure using subnanometre (coherent) probes, the imaging conditions play an important role.

Epoxy nano-magnetic composites exhibit remarkable and promising properties by synergistically combining the properties of epoxy resin and magnetic nanofillers. The current study deals with the synthesis of Fe3O4, NiFe2O4, and CoFe2O4 nanoparticles and their respective nanoparticles-doped epoxy composites, as well as the structural, optical, and dielectric characterization of the resultant nano-composites. To investigate the surface morphology of the synthesized nanoparticles, field emission electron microscopy (FESEM) analysis was employed. By measuring electron diffraction spectroscopy (EDS), the presence of various chemicals was verified. X-ray diffraction (XRD) was used to determine the structural details of the synthesized nanoparticles and nanoparticles-doped epoxy composites. The structural chemistry and surface functionality of the nano-epoxy composites were investigated using Fourier transform infrared spectroscopy (FTIR). The magnetic properties of the synthesized nanoparticles and nanoparticles loaded epoxy composites were also studied using a vibrating sample magnetometer (VSM). UV–visible reflection spectroscopy was also carried out to find the optical properties of the synthesized nanoparticles, neat (undoped) epoxy, and nanoparticles-doped epoxy composites. Dielectric spectroscopy measurements of nanoparticles-doped epoxy composites were performed using an Agilent E4980A precision LCR (Inductance Capacitance Resistance) meter with an Agilent 16451B-test fixture LCR and vector network analyzer (VNA) in the frequency span of 10 kHz to 2 MHz and 200 MHz to 20 GHz, respectively. The influence of the synthesized nanoparticles on the neat (undoped) epoxy composites and the results in view of future applications are fully discussed.

The emerging field of 3D electron diffraction (3D ED) opens new opportunities for structure determination from sub-micrometre-sized crystals. Although the foundations of this technology emerged earlier, the past decade has seen developments in cryo-electron microscopy and (X-ray) crystallography that particularly enable the widespread use of 3D ED. This Perspective describes to chemists and chemical crystallographers just how similar electron and X-ray diffraction are and discusses their complementary aspects. We wish to establish 3D ED in the broader chemistry community, such that electron crystallography becomes a common part of the analytical chemistry toolkit. With a suitable instrument at their disposal, every skilled crystallographer can quickly learn to perform structure determinations using 3D ED.

This paper presents a review of the developments in Convergent Beam Electron Diffraction (CBED), a technique widely used for determination of structure, symmetry details and atom positions in a crystal as small as 20A in size. The understanding of this technique is related to the rapid advancements in the field of transmission electron microscopy with respect to development of coherent, finer probes and electron optics for higher spatial resolution. Energy filtering devices enable imaging of several finer features in the CBED pattern from which useful information about a crystal can be obtained. These include (i) three-dimensional information about the reciprocal lattice, (ii) point and space group symmetry details, (iii) lattice parameter from regions as fine as 2 nm, (iv) atom positions within a unit cell and (v) defects in crystals and (vi) thickness. Due to abundant data obtained from microscopic regions, this technique is unique and finds wide application in materials characterization. It has been used for studying problems like identification of the presence of lattice strain, identification of point defects etc. in a material used often in the nuclear industry, namely 9Cr-1Mo steel. The present paper provides the current status of CBED starting from its historical development, the information that can be obtained and its use in a variety of applications.

The structures of two laser processed ternary intermetallic phases, Al16Ti6(Fe or Ni)7, have been studied by using electron diffraction and microscopy. A convergent beam electron diffraction (CBED) technique for structure determination is described based upon the principle of kinematic interpretation of large angle systematic reflections in CBED disks. The structure type of phases Al16Ti6(Fe or Ni)7 is characterized as the Mn23Th6(cF116)-type, the same as those of relevant phases Cu16Mg6Si7 and Al50Ti25Fe25 etc., by using the CBED technique. Various errors involved in the analyses are also discussed.

In recent years, significant progress has been made towards a solution for the general problem of crystal structure determination by convergent beam electron diffraction (CBED). Even if we consider only perfectly ordered, periodic crystals defined by one of the conventional space groups, diffraction methods based on a focussed sub-micron beam of electrons are applicable to several related sets of structural problems that are not accessible to conventional X-ray or neutron diffraction techniques. We assume here that the space group either is known or has been determined from CBED patterns and that phases and amplitudes for some subset of the structure factors are required. Two limiting cases have been explored in some detail. For crystals where the atomic parameters and Debye-Waller factors are known accurately from high quality X-ray data, information on the charge redistribution for bonding electrons is available from precise measurements of the low order structure factors. Following the original research of Kambe, some recent work has demonstrated that accurate structure amplitudes and three-beam phase invariants can be extracted from the dynamical intensity distribution in CBED reflections. In principle, this approach is completely general but considerable labour would be required to extract sufficient data to solve the structure of an unknown crystal, whereas a large set of kinematic intensities is acquired from a single X-ray pattern.

Continuous Serial Electron Diffraction (SerialED) is an emerging technique with significant potential across structural biology, chemistry, pharmaceuticals, and materials science, enabling crystal structure determination from beam-sensitive samples.[1] Yet widespread adoption remains limited, in part because data processing is perceived as complex.We introduce a streamlined, Python–based processing suite tailored to continuous SerialED. Fast, robust preprocessing is followed by indexing and integration routines adapted from X-ray free electron laser (XFEL) data processing, and optimised to tackle the specific challenges of electron–diffraction data. The pipeline carries datasets seamlessly from raw diffraction frames to a refinement–ready HKL file, while comprehensive logging ensures full traceability and reproducibility.A lightweight graphical interface ties the workflow together, allowing users to launch jobs, get feedback and adjust parameters without the need for scripting. By removing technical hurdles and shortening the learning curve, the package aims to lower the barrier to routine continuous SerialED across a wide range of research fields.A beta version of the software will be provided under an MIT open-source licence.

Influence of synthesis temperature on oxygen exchange behavior of electrode material PrBaFe2O6−δ

Structural studies are essential for understanding formation, growth stability and physical properties of quasicrystals and related phases. Diffraction is a powerful tool for studying order and disorder in these materials. Electron diffraction has played a key role in the discovery of icosahedral [1, 2], decagonal [3] and dodecagonal [4] quasicrystals and their characterization. In many quasicrystalline alloys, the size of quasicrystalline grains being small (typically 1 um), only electron diffraction and X-ray or neutron powder diffraction methods were feasible. Inconvenient with electron diffraction is the importance of multiple Bragg scattering making intensity calculations generally hard to handle. The disadvantage of powder methods is that the three-dimensional diffraction patterns of all individual small single grains are angularly averaged and reduced to one-dimensional informations. It is one of the reasons to go further in the structure determination of these materials, since the beginning, that efforts were undertaken to prepare large single grains Of course, this rests on the assumption that the quasicrystal is stable at least in some composition and temperature range. With the elaboration of large single grains with triacontahedral shapes, Al6Li3Cu was the first reported stable icosahedral quasicrystal [5]. This opened the way for structure determination by X-ray or neutron diffraction. The use of X-ray synchrotron beam combining high-flux and high-resolution is particularly well-suited for studying very weak diffraction peaks that allow to distinguish between quasiperiodic order and complex domain arrangements of approximant phases.

A new approach to the problem of crystal structure determination by electron diffraction is described based upon the intensities of higher-order Laue-zone (HOLZ) reflections in convergent-beam electron diffraction (CBED) patterns. Along a major zone axis, a subset of symmetry-related atoms may project into separate string potentials associated with localized Bloch states. In a quasi-kinematic limit, the amplitudes of HOLZ excess lines diffracted from the Bloch states are proportional to the partial structure factors for these atoms. If a structure is unknown, the Bloch states cannot be calculated but it is shown that the conditional Patterson transform of the HOLZ intensities around suitable axes may include narrow correlation peaks that identify interatomic vectors. This approach was tested by analysis of a metastable Al–Ge phase with space group R{\bar 3}c. A transform of HOLZ intensities measured around the c axis showed peaks displaced by only 0.21 Å from the screw axes, consistent with Ge atoms in the 18(e) positions. Although Al atoms were not visible in the Patterson maps, the crystal structure with nominal composition Al6Ge5 was identified as isostructural with the Zn4Sb3 phase by comparison of observed and calculated X-ray powder intensities.

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.

Picosecond electron diffraction from molecules aligned by dissociation

Serial electron diffraction (SerialED), which applies a snapshot data acquisition strategy for each crystal, was introduced to tackle the problem of radiation damage in the structure determination of beam-sensitive materials by three-dimensional electron diffraction (3DED). The snapshot data acquisition in SerialED can be realized using both transmission and scanning transmission electron microscopes (TEM/STEM). However, the current SerialED workflow based on STEM setups requires special external devices and software, which limits broader adoption. Here, we present a simplified experimental implementation of STEM-based SerialED on Thermo Fisher Scientific STEMs using common proprietary software interfaced through Python scripts to automate data collection. Specifically, we utilize TEM Imaging and Analysis (TIA) scripting and TEM scripting to access the STEM functionalities of the microscope, and DigitalMicrograph scripting to control the camera for snapshot data acquisition. Data analysis adapts the existing workflow using the software CrystFEL, which was developed for serial X-ray crystallography. Our workflow for STEM SerialED can be used on any Gatan or Thermo Fisher Scientific camera. We apply this workflow to collect high-resolution STEM SerialED data from two aluminosilicate zeolites, zeolite Y and ZSM-25. We demonstrate, for the first time, ab initio structure determination through direct methods using STEM SerialED data. Zeolite Y is relatively stable under the electron beam, and STEM SerialED data extend to 0.60 Å. We show that the structural model obtained using STEM SerialED data merged from 358 crystals is nearly identical to that using continuous rotation electron diffraction data from one crystal. This demonstrates that accurate structures can be obtained from STEM SerialED. Zeolite ZSM-25 is very beam-sensitive and has a complex structure. We show that STEM SerialED greatly improves the data resolution of ZSM-25, compared with serial rotation electron diffraction (SerialRED), from 1.50 to 0.90 Å. This allows, for the first time, the use of standard phasing methods, such as direct methods, for the ab initio structure determination of ZSM-25.

Determining the atomic structure of materials and molecules is essential for understanding their properties and functions in both materials and life sciences.X-ray crystallography has long been the standard technique, but its reliance on large, well-ordered crystals presents challenges for certain materials, such as membrane proteins [1].Microcrystal electron diffraction (MicroED) has proven effective for solving the structures of biomaterials and small molecules [2].However, its reliance on continuous crystal rotation and high-energy electron exposure limits its applicability to beam-sensitive materials.Recently, serial nano-electron diffraction (SerialNED) has been developed for structure determination of small molecules [3] and proteins [4].Adapted from the snapshot data-collection approach used in serial X-ray crystallography, SerialNED offers key advantages over traditional X-ray diffraction, including lower sample requirements, reduced radiation damage, and comparable resolution [5].A major challenge in SerialNED is the preparation of nanocrystals.Here, we present a novel approach that employs a femtosecond (fs) laser to precisely control the crystallization process [6], enabling the rapid formation of nanocrystals for electron diffraction analysis.This method enhances nucleation efficiency, producing single crystals of organic molecules and proteins with minimal material consumption.By streamlining nanocrystal production, it significantly accelerates the structure determination process compared to conventional batch crystallization techniques.One of our target materials is cytosine, a fundamental DNA base.When cytosine dissolves in water, it forms cytosine monohydrate crystals, which are typically challenging to prepare as nanocrystals suitable for transmission electron microscopy (TEM) analysis due to difficulties in microtoming.Cytosine serves as an excellent testing material not only because it is a DNA base but also because it readily crystallizes [7].After preparing the sample solution, a femtosecond laser (Ti:Sapphire, 800 nm, 35 fs, 1kHz) irradiates it on electron microscopy grids, promoting crystal nucleation.The grids are then dried using a suction unit and prepared for TEM analysis.Using laser-induced crystallization, we successfully generated a relatively large quantity of nanometer-thin cytosine monohydrate crystals.The unit cell parameters and morphology of cytosine monohydrate crystals grown using the femtosecond laser match those grown via conventional methods.These crystals exhibited high-quality diffraction patterns, as illustrated in Fig. 1C.We then applied serial nano-electron diffraction (SerialNED) to these samples, determining the structure with sub-angstrom resolution using a 90 kV electron microscope at room temperature.The experiments were carried out using a Hitachi HT7800 transmission and scanning transmission electron microscope (TEM/STEM), coupled with an X-Spectrum Amber 750K detector, to determine the structure of cytosine monohydrate.Electron diffraction patterns were collected sequentially using the Azorus software package (Hitachi High-Tech Canada Inc.) to map the crystal coordinates.Over 10,000 diffraction patterns were obtained from the sample, enabling the structure to be determined with high resolution (Fig. 2).In summary, femtosecond laser-induced crystallization provides a powerful approach to accelerate and control crystallization processes.This technique enables the production of high-quality single crystals suitable for electron diffraction.By combining this method with SerialNED, it represents a high-throughput solution for structural determination across a wide range of materials [9].