The generation of defects during dynamic compression is well established; however, directly imaging their formation has not been spatially resolved routinely. To address this, we developed an x-ray topography diagnostic to work toward the observation of spatially resolved strain gradients associated with deformation in ambient and shocked materials at the Matter at Extreme Conditions beamline of the Linac Coherent Light Source (LCLS). X-ray topography is a near field technique that reveals defects in single-crystal samples as spatially varying intensity contrast within the diffracted x-ray beam. Owing to its high-quality single-crystal structure and exceptional strength, diamond is an outstanding material for investigating defect generation at both ambient and extreme conditions. Using single x-ray pulses from LCLS, we obtained high-quality topographic images from 〈100〉, 〈110〉, and 〈111〉 oriented diamond crystals under ambient conditions. We then drove laser-generated shocks over a range of stresses to explore whether x-ray topography can visualize the real-time creation of defects governing the onset of plasticity.

Dark field x-ray microscopy (DXFM) can visualize microstructural distortions in bulk crystals. Using the femtosecond x-ray pulses generated by x-ray free-electron lasers (XFELs), DFXM can achieve sub-μm spatial resolution and <100 fs time resolution simultaneously. In this paper, we demonstrate ultrafast DFXM measurements at the European XFEL to visualize an optically driven longitudinal strain wave propagating through a diamond single crystal. We also present two DFXM scanning modalities that are new to the XFEL sources: spatial 3D and 2D axial-strain scans with sub-μm spatial resolution. With this progress in XFEL-based DFXM, we discuss new opportunities to study multi-timescale spatiotemporal dynamics of microstructures.

Dark-field X-ray microscopy (DFXM) is a full-field imaging technique that non-destructively maps the structure and local strain inside deeply embedded crystalline elements in three dimensions. In DFXM, an objective lens is placed along the diffracted beam to generate a magnified projection image of the local diffracted volume. This work explores contrast methods and optimizes the DFXM setup specifically for the case of mapping dislocations. Forward projections of detector images are generated using two complementary simulation tools based on geometrical optics and wavefront propagation, respectively. Weak and strong beam contrast and the mapping of strain components are studied. The feasibility of observing dislocations in a wall is elucidated as a function of the distance between neighbouring dislocations and the spatial resolution. Dislocation studies should be feasible with energy band widths of 10 −2 , of relevance for fourth-generation synchrotron and X-ray free-electron laser sources.

The structures, strain fields, and defect distributions in solid materials underlie the mechanical and physical properties across numerous applications. Many modern microstructural microscopy tools characterize crystal grains, domains and defects required to map lattice distortions or deformation, but are limited to studies of the (near) surface. Generally speaking, such tools cannot probe the structural dynamics in a way that is representative of bulk behavior. Synchrotron X-ray diffraction based imaging has long mapped the deeply embedded structural elements, and with enhanced resolution, Dark Field X-ray Microscopy (DFXM) can now map those features with the requisite nm-resolution. However, these techniques still suffer from the required integration times due to limitations from the source and optics. This work extends DFXM to X-ray free electron lasers, showing how the 10^12 photons per pulse available at these sources offer structural characterization down to 100 fs resolution (orders of magnitude faster than current synchrotron images). We introduce the XFEL DFXM setup with simultaneous bright field microscopy to probe density changes within the same volume. This work presents a comprehensive guide to the multi-modal ultrafast high-resolution X-ray microscope that we constructed and tested at two XFELs, and shows initial data demonstrating two timing strategies to study associated reversible or irreversible lattice dynamics.

The dynamics of lattice vibrations govern many material processes, such as acoustic wave propagation, displacive phase transitions, and ballistic thermal transport. The maximum velocity of these processes and their effects is determined by the speed of sound, which therefore defines the temporal resolution (picoseconds) needed to resolve these phenomena on their characteristic length scales (nanometers). Here, we present an X-ray microscope capable of imaging acoustic waves with subpicosecond resolution within mm-sized crystals. We directly visualize the generation, propagation, branching, and energy dissipation of longitudinal and transverse acoustic waves in diamond, demonstrating how mechanical energy thermalizes from picosecond to microsecond timescales. Bulk characterization techniques capable of resolving this level of structural detail have previously been available on millisecond time scales-orders of magnitude too slow to capture these fundamental phenomena in solid-state physics and geoscience. As such, the reported results provide broad insights into the interaction of acoustic waves with the structure of materials, and the availability of ultrafast time-resolved dark-field X-ray microscopy opens a vista of new opportunities for 3D imaging of materials dynamics on their intrinsic submicrosecond time scales.

The properties of semiconductors and functional dielectrics are defined by their response in electric fields, which may be perturbed by defects and the strain they generate. In this work, we demonstrate how diffraction-based X-ray microscopy techniques may be utilized to image the electric field in insulating crystalline materials. By analysing a prototypical ferro- and piezoelectric material, BaTiO$_{3}$, we identify trends that can guide experimental design towards imaging the electric field using any diffraction-based X-ray microscopy technique. We explain these trends in the context of dark-field X-ray microscopy, but the framework is also valid for Bragg scanning probe X-ray microscopy, Bragg coherent diffraction imaging and Bragg X-ray ptychography. The ability to quantify electric field distributions alongside the defects and strain already accessible via these techniques offers a more comprehensive picture of the often complex structure-property relationships that exist in many insulating and semiconducting materials.

DF-XRM_vis is a visualization tool to aid in planning, execution, and data analysis of dark-field X-ray microscopy experiments.The toolkit is built in python and has a streamlit interface, as well as a jupyterlab example.The highlight of the toolkit is generating 3D models of experimental geometry, that are rendered together with the unit cell of the material.As the streamlit application is hosted on a publicly available address, the toolkit is available also to researchers without programming experience.

Dark-field X-ray microscopy is a diffraction-based synchrotron imaging technique capable of imaging defects in the bulk of extended crystalline samples. Numerical simulations are presented of image formation in such a microscope using numerical integration of the dynamical Takagi-Taupin equations and wavefront propagation. The approach is validated by comparing simulated images with experimental data from a near-perfect single crystal of diamond containing a single stacking-fault defect in the illuminated volume.

Dark-field x-ray microscopy (DFXM) is an x-ray imaging technique for mapping three-dimensional (3D) lattice strain and rotation in bulk crystalline materials. At present, these maps of local structural distortions are derived from the raw intensity images using an incoherent analysis framework. In this work, we describe a coherent, Fourier ptychographic approach that requires little change in terms of instrumentation and acquisition strategy, and may be implemented on existing DFXM instruments. We demonstrate the method experimentally and are able to achieve quantitative phase reconstructions of thin film samples and maps of the aberrations in the objective lens. The method holds particular promise for the characterization of crystalline materials containing weak structural contrast.

Ferroelectrics are being increasingly called upon for electronic devices in extreme environments. Device performance and energy efficiency is highly correlated to clock frequency, operational voltage, and resistive loss. To increase performance it is common to engineer ferroelectric domain structure with highly-correlated electrical and elastic coupling that elicit fast and efficient collective switching. Designing domain structures with advantageous properties is difficult because the mechanisms involved in collective switching are poorly understood and difficult to investigate. Collective switching is a hierarchical process where the nano- and mesoscale responses control the macroscopic properties. Using chemical solution synthesis, epitaxially nearly-relaxed (100) BaTiO3 films are synthesized. Thermal strain induces a strongly-correlated domain structure with alternating domains of polarization along the [010] and [001] in-plane axes and 90° domain walls along the [011] or [01 1 ¯ $\bar{1}$ ] directions. Simultaneous capacitance-voltage measurements and band-excitation piezoresponse force microscopy revealed strong collective switching behavior. Using a deep convolutional autoencoder, hierarchical switching is automatically tracked and the switching pathway is identified. The collective switching velocities are calculated to be ≈500 cm s-1 at 5 V (7 kV cm-1 ), orders-of-magnitude faster than expected. These combinations of properties are promising for high-speed tunable dielectrics and low-voltage ferroelectric memories and logic.

Dark-field X-ray microscopy (DFXM) is a nondestructive full-field imaging technique providing three dimensional mapping of microstructure and local strain fields in deeply embedded crystalline elements. This is achieved by placing an objective lens in the diffracted beam, giving a magnified projection image. So far, the method has been applied with a time resolution of milliseconds to hours. In this work, we consider the feasibility of DFXM at the picosecond time scale using an X-ray free electron laser source and a pump-probe scheme. We combine thermomechanical strain wave simulations with geometrical optics and wavefront propagation optics to simulate DFXM images of phonon dynamics in a diamond single crystal. Using the specifications of the XCS instrument at the Linac Coherent Light Source (LCLS) as an example results in simulated DFXM images clearly showing the propagation of a strain wave.

Ferroelectric properties of films can be tailored by strain engineering, but a wider space for property engineering can be opened by including crystal anisotropy. Here, we demonstrate a huge anisotropy in the dielectric and ferroelectric properties of BaTiO3 films. Epitaxial BaTiO3 films deposited on (100), (110), and (111) SrTiO3 substrates were fabricated by chemical solution deposition. The films were tensile-strained due to thermal strain confirmed by the enhanced Curie temperature. A massive anisotropy in the dielectric constant, dielectric tunability, and ferroelectric hysteresis loops was observed depending on the in-plane direction probed and the orientation of the films. The anisotropy was low for (111) BaTiO3, while the anisotropy was particularly strong for (110) BaTiO3, reflecting the low in-plane rotational symmetry. The anisotropy also manifested at the level of the ferroelectric domain patterns in the films, providing a microscopic explanation for the macroscopic response. This study demonstrates that the properties of ferroelectric films can be tailored not only by strain but also by crystal orientation. This is particularly interesting for multilayer stacks where the strain state is defined by the boundary conditions. We propose that other materials can be engineered in a similar manner by utilizing crystal anisotropy.

Chemical solution deposition (CSD) is a versatile method to fabricate oxide films. Here, the structure and local variations in the chemical composition of BaTiO3 (BTO) films prepared by CSD on (100), (110), and (111) SrTiO3 (STO) substrates were examined by transmission electron microscopy. The films were shown to be epitaxial and the relaxation of the films occurred by the formation of edge dislocations at the substrate–film interfaces. The Burgers vectors of the dislocations were determined to be a⟨010⟩, a[11¯0] and a[001], and a⟨110⟩ for the (100), (110), and (111) films, respectively. Due to the difference in thermal expansion between STO and BTO, the films are demonstrated to be under tensile strain. Furthermore, the boundaries between each deposited layer in the BTO films were found to be Ba-deficient in all cases. In the case of the (111) oriented film, defects like an anti-phase boundary or a thin layer with a twinned crystal structure were identified at the boundary between each deposited layer. Moreover, a larger grain was observed at the film surface with a twinned crystal structure. The interdiffusion length of A-cations at the STO–BTO interface, studied by electron energy-loss spectroscopy, was found to be 3.4, 5.3, and 5.3 nm for the (100), (110), and (111) oriented films, respectively. Interdiffusion of cations across the STO–BTO interface was discussed in relation to cation diffusion in bulk BTO and STO. Despite the presence of imperfections demonstrated in this work, the films possess excellent ferroelectric properties, meaning that none of the imperfections are detrimental to the ferroelectric properties.

Ferroelectric domain walls are promising quasi-2D structures that can be leveraged for miniaturization of electronics components and new mechanisms to control electronic signals at the nanoscale. Despite the significant progress in experiment and theory, however, most investigations on ferroelectric domain walls are still on a fundamental level, and reliable characterization of emergent transport phenomena remains a challenging task. Here, we apply a neural-network-based approach to regularize local I ( V )-spectroscopy measurements and improve the information extraction, using data recorded at charged domain walls in hexagonal (Er 0.99 ,Zr 0.01 )MnO 3 as an instructive example. Using a sparse long short-term memory autoencoder, we disentangle competing conductivity signals both spatially and as a function of voltage, facilitating a less biased, unconstrained and more accurate analysis compared to a standard evaluation of conductance maps. The neural-network-based analysis allows us to isolate extrinsic signals that relate to the tip-sample contact and separating them from the intrinsic transport behavior associated with the ferroelectric domain walls in (Er 0.99 ,Zr 0.01 )MnO 3 . Our work expands machine-learning-assisted scanning probe microscopy studies into the realm of local conductance measurements, improving the extraction of physical conduction mechanisms and separation of interfering current signals.

Aqueous chemical solution deposition (CSD) of lead-free ferroelectric K0.5Na0.5NbO3 (KNN) thin films has a great potential for cost-effective and environmentally friendly components in microelectronics. Phase purity of KNN is, however, a persistent challenge due to the volatility of alkali metal oxides, usually countered by using excess alkali metals in the precursor solutions. Here, we report on the development of two different aqueous precursor solutions for CSD of KNN films, and we demonstrate that the decomposition process during thermal processing of the films is of detrimental importance for promoting nucleation of KNN and suppressing the formation of secondary phases. Based on thermal analysis, X-ray diffraction and IR spectroscopy of films as well as powders prepared from the solutions, it was revealed that the decomposition temperature can be controlled by chemistry resulting in phase pure KNN films. A columnar microstructure with out-of-plane texturing was observed in the phase pure KNN films, demonstrating that the microstructure is directly coupled to the thermal processing of the films.

Relaxor ferroelectrics exhibit superior properties for converting mechanical energy into electrical, and vice versa, but the structural disorder hampers an understanding of structureproperty relationships, and impedes rational design of new, lead-free materials. Bi0.5K0.5TiO3 (BKT) is a prototypical lead-free relaxor ferroelectric, but the microscopic origins of polarization, nature of the ferroelectric transition (TC) and structural changes across the tetragonal to pseudo-cubic transition (T2) are poorly understood. Here the local and intermediate structure of BKT is studied from room temperature to above TC by pair distribution functions (PDF) from synchrotron X-ray total scattering experiments and complemented by ab initio molecular dynamics (AIMD) simulations. The local structure varies smoothly across T2 as well as TC, in contrast to the abrupt changes at TC inferred from conventional diffraction. Ferroelectric distortions are larger on the local scale than in the average structure, with polar Ti4+ displacements prevailing above TC. We find that local polar regions partly cancel each other below TC, while completely averaging out above, implying that BKT goes through a transition from partial to complete disorder across TC.

In this paper, a new method to characterize ferroelectric thin films with interdigitated electrodes is presented. To obtain accurate properties, all parasitic contributions should be subtracted from the measurement results and accurate models for the ferroelectric film are required. Hence, we introduce a phenomenological model for the parasitic capacitance. Moreover, two common analytical models based on conformal transformations are compared and used to calculate the capacitance and the electric field. With a thin film approximation, new simplified electric field and capacitance formulas are derived. By using these formulas, more consistent CV, PV and stress-field loops for samples with different geometries are obtained. In addition, an inhomogeneous distribution of the permittivity due to the nonuniform electric field is modelled by finite element simulation in an iterative way. We observed that this inhomogeneous distribution can be treated as a homogeneous one with an effective value of the permittivity.

Relaxor ferroelectrics exhibit superior properties for converting mechanical energy into electrical energy, and vice versa, but the structural disorder hampers an understanding of structure-property relationships and impedes rational design of new, lead-free materials. Bi0.5K0.5TiO3 (BKT) is a prototypical lead-free relaxor ferroelectric, but the microscopic origins of polarization, nature of the ferroelectric transition (T-C), and structural changes across the tetragonal to pseudocubic transition (T-2) are poorly understood. Here the local and intermediate structure of BKT is studied from room temperature to above T-C by pair distribution functions (PDFs) from synchrotron X-ray total scattering experiments and complemented by ab initio molecular dynamics (AIMD) simulations. The local structure varies smoothly across T-2 as well as T-C, in contrast to the abrupt changes at T-C inferred from conventional diffraction. Ferroelectric distortions are larger on the local scale than in the average structure, with polar Ti4+ displacements prevailing above T-C. We find that local polar regions partly cancel each other below T-C, while completely averaging out above, implying that BKT goes through a transition from partial to complete disorder across T-C.

Ferroelectric BaTiO3 is widely used in capacitors, but the low Curie temperature limits a further use of BaTiO3. In this work we present an aqueous chemical solution deposition (CSD) route for BaTiO3 thin films, demonstrating that organic solvents are not required for CSD. Textured BaTiO3 thin films were deposited on SrTiO3 substrates. The in-plane dielectric properties were investigated using interdigitated electrodes and ferroelectric switching was observed up to 160±5 °C. The increased Curie temperature is proposed to result from thermal strain due to a mismatch in thermal expansion coefficient between the film and the substrate, and is in good agreement with the theory of strain engineering in BaTiO3. Finally, the decomposition and crystallization of BaTiO3 during thermal treatment were determined by the combination of thermal analysis, IR spectroscopy and X-ray diffraction of powder prepared from the solution.

The accurate evaluation of ferroelectric thin films operated with interdigitated electrodes is quite a complex task. In this article, we show how to correct the electric field and the capacitance in order to obtain identical polarization and CV loops for all geometrical variants. The simplest model is compared with corrections derived from Schwartz-Christoffel transformations, and with finite element simulations. The correction procedure is experimentally verified, giving almost identical curves for a variety of gaps and electrode widths. It is shown that the measured polarization change corresponds to the average polarization change in the center plane between the electrode fingers, thus at the position where the electric field is most homogeneous with respect to the direction and size. The question of maximal achievable polarization in the various possible textures, and compositional types of polycrystalline lead zirconate titanate thin films is revisited. In the best case, a soft (110) textured thin film with the morphotropic phase boundary composition should yield a value of 0.95Ps, and in the worst case, a rhombohedral (100) textured thin film should deliver a polarization of 0.74Ps.