Scanning X-ray Nanodiffraction Research Articles

Optical Control of Adaptive Nanoscale Domain Networks.

Adaptive networks can sense and adjust to dynamic environments to optimize their performance. Understanding their nanoscale responses to external stimuli is essential for applications in nanodevices and neuromorphic computing. However, it is challenging to image such responses on the nanoscale with crystallographic sensitivity. Here, the evolution of nanodomain networks in (PbTiO3)n/(SrTiO3)n superlattices (SLs) is directly visualized in real space as the system adapts to ultrafast repetitive optical excitations that emulate controlled neural inputs. The adaptive response allows the system to explore a wealth of metastable states that are previously inaccessible. Their reconfiguration and competition are quantitatively measured by scanning x-ray nanodiffraction as a function of the number of applied pulses, in which crystallographic characteristics are quantitatively assessed by assorted diffraction patterns using unsupervised machine-learning methods. The corresponding domain boundaries and their connectivity are drastically altered by light, holding promise for light-programable nanocircuits in analogy to neuroplasticity. Phase-field simulations elucidate that the reconfiguration of the domain networks is a result of the interplay between photocarriers and transient lattice temperature. The demonstrated optical control scheme and the uncovered nanoscopic insights open opportunities for the remote control of adaptive nanoscale domain networks.

X-ray nano-imaging of defects in thin film catalysts via cluster analysis

Functional properties of transition-metal oxides strongly depend on crystallographic defects; crystallographic lattice deviations can affect ionic diffusion and adsorbate binding energies. Scanning x-ray nanodiffraction enables imaging of local structural distortions across an extended spatial region of thin samples. Yet, localized lattice distortions remain challenging to detect and localize using nanodiffraction, due to their weak diffuse scattering. Here, we apply an unsupervised machine learning clustering algorithm to isolate the low-intensity diffuse scattering in as-grown and alkaline-treated thin epitaxially strained SrIrO3 films. We pinpoint the defect locations, find additional strain variation in the morphology of electrochemically cycled SrIrO3, and interpret the defect type by analyzing the diffraction profile through clustering. Our findings demonstrate the use of a machine learning clustering algorithm for identifying and characterizing hard-to-find crystallographic defects in thin films of electrocatalysts and highlight the potential to study electrochemical reactions at defect sites in operando experiments.

Operando X-Ray Diffraction Nanoimaging of Advanced Cathodes

Techniques capable of probing active materials in situ are increasingly needed to link cell performance data with nanostructural evolution inside functional devices. Rapid improvements in spatial and temporal resolution of X-ray nanomicroscopy and high-energy diffraction facilitated by new 4th-gen synchrotrons offer a powerful platform for investigating phase transitions inside advanced cathode materials. We show how the latest methodologies can be used to evaluate the mechanism of phase transitions at the nanoscale, linked to degradation processes inside commercially relevant cells."Single crystal" cathode active materials have garnered incredible academic and industrial interest in the past several years. Despite extensive electrochemical performance validation, there remain very few tools capable of evaluating the quality and consistency of these materials. Scanning X-ray nanodiffraction microscopy reveals the hidden microstructure and defects inside nominally single crystal cathode particles established during their fabrication. In situ nanodiffraction imaging provides further insight towards the link between this microstructure and functional properties such as high voltage stability inside individual crystallites during cycling.

Mesoscale Ordering of Phycocyanin Molecules in Langmuir-Blodgett Multilayers.

Phycocyanin molecules, which are part of light-harvesting complexes in cyanobacteria, can be assembled into mesoscale multilayer nanofilms by the Langmuir-Blodgett technique. Results obtained by quartz crystal microbalance and atomic force microscopy confirm the homogeneity and reproducibility of phycocyanin Langmuir-Blodgett multilayer deposition. We show by cryo-electron microdiffraction that amorphous phycocyanin Langmuir-Blodgett multilayers form, after annealing at 150 °C and cooling to room temperature, a layered nanofibrillar lattice with rotational disorder. Scanning X-ray nanodiffraction suggests that structural transformation is not homogeneous through the film but limited to patches of up to about 10 μm diameter.

Emergence of amyloidic fibrillation in 2D-ordered Langmuir–Blodgett protein multilayers upon heating

Langmuir–Blodgett protein nanofilms can serve as templates for nucleation and growth of protein crystals. This functionality can be enhanced by thermal annealing. While surface ordering of the multilayered nanofilms and an improvement of the correlation between the layers during thermal annealing have been revealed by atomic force microscopy and grazing-incidence small-angle x-ray scattering, information on the structure developing in the bulk of nanofilms is lacking. In this paper, we report on scanning x-ray nanodiffraction experiments of penicillin-G-acylase multilayers deposited on Si3N4 membranes and annealed at 150 °C. While the annealed multilayer has remained mostly featureless, we observe locally globular aggregates and filamentous spherulites based on nanofibrillar subunits with cross-β amyloidic motifs.

Indentation response of a superlattice thin film revealed by in-situ scanning X-ray nanodiffraction

Nanocrystalline materials such as thin films, and in particular, multilayers with a periodicity in the nanometer range, i.e. superlattice films, possess properties that cannot be found in their coarse-grained bulk counterparts. Mechanical characterization of such structures is therefore of high interest, but also very challenging, due to the small length scales involved and has therefore most often been performed ex-situ using electron microscopy. In this work, however, we report on the first in-situ micromechanical analysis of a CrN-AlN superlattice thin film cross-section. The sample was deposited using reactive magnetron sputtering and sublayer thicknesses were chosen so as to stabilize AlN in its cubic crystal structure. Using a synchrotron X-ray nanoprobe, maps of internal stresses and morphological changes were tracked by means of wide-angle X-ray diffraction and simultaneous small-angle X-ray scattering, while the sample was loaded to various degrees with a wedged diamond tip. The results reveal a high compressive strength of about 13 GPa, while through-thickness cracks form, following tensile stresses >1.4 GPa and thereby provide a relaxation mechanism. Layer rotation up to several degrees and significant layer compression up to 7% were also found, but along with the internal stress response, their nature is mostly elastic, meaning that in the post-loading state only a fraction of the effects observed under load remains.

Strain mapping inside an individual processed vertical nanowire transistor using scanning X-ray nanodiffraction.

Semiconductor nanowires in wrapped, gate-all-around transistor geometry are highly favorable for future electronics. The advanced nanodevice processing results in strain due to the deposited dielectric and metal layers surrounding the nanowires, significantly affecting their performance. Therefore, non-destructive nanoscale characterization of complete devices is of utmost importance due to the small feature sizes and three-dimensional buried structure. Direct strain mapping inside heterostructured GaSb-InAs nanowire tunnel field-effect transistor embedded in dielectric HfO2, W metal gate layers, and an organic spacer is performed using fast scanning X-ray nanodiffraction. The effect of 10 nm W gate on a single embedded nanowire with segment diameters down to 40 nm is retrieved. The tensile strain values reach 0.26% in the p-type GaSb segment of the transistor. Supported by the finite element method simulation, we establish a connection between the Ar pressure used during the W layer deposition and the nanowire strain state. Thus, we can benchmark our models for further improvements in device engineering. Our study indicates, how the significant increase in X-ray brightness at 4th generation synchrotron, makes high-throughput measurements on realistic nanoelectronic devices viable.

Nanoscale X-Ray Diffraction of Silk Fibers

This report focuses on current possibilities and perspectives of scanning X-ray nanodiffraction for probing nanoscale heterogeneities in silk fibers such as nanofibrillar skin-core morphologies, nanocrystalline inclusions and fine fibers down to submicron diameters.

Strain Distribution Induced in SOI Photonic Substrate by Through Silicon via Using Advanced Scanning X-Ray Nano-Diffraction

In 3-D integration, dice are vertically interconnected with through silicon via (TSV), which consist of holes etched in a thinned silicon substrate and filled with copper. This process induces thermal strain in surrounding silicon. New trends in 3-D integration imply the fabrication of Si photonic devices like waveguides in silicon-on-insulator (SOI) substrates containing TSVs. Thus, a quantitative analysis of strain in active areas around TSVs is mandatory. In this paper, the strain induced by the TSVs in both the bulk silicon and the SOI layer was investigated by using advanced scanning X-ray nano-diffraction. The crystallographic orientation offset between the separated silicon areas allows decorrelation of the strain in the Si layer of the SOI and Si substrate. Using synchrotron radiation, 2-D quicK continuous mapping of the strain in a region of 50 $ \mu \text{m}\,\, \times $ 50 $ \mu \text{m}$ with 500 nm spatial resolution was performed around a single TSV at room temperature and during in-situ annealing at 460 °C. The strain field induced by the TSV appears negligible in both silicon areas. The effect of in-situ annealing on the strain distribution is surprisingly weak. In the SOI active layer, the strain map mimics the surface pattern generated by the photonic devices processed at high temperature in this thin layer.

Lattice tilt and strain mapped by X-ray scanning nanodiffraction in compositionally graded SiGe/Si microcrystals

The scanning X-ray nanodiffraction technique is used to reconstruct the three-dimensional distribution of lattice strain and Ge concentration in compositionally graded Si1−x Ge x microcrystals grown epitaxially on Si pillars. The reconstructed crystal shape qualitatively agrees with scanning electron micrographs and the calculated three-dimensional distribution of lattice tilt quantitatively matches finite-element method simulations. The grading of the Ge content obtained from reciprocal-space maps corresponds to the nominal grading of the epitaxial growth recipe. The X-ray measurements confirm strain calculations, according to which the lattice curvature of the microcrystals is dominated by the misfit strain, while the thermal strain contributes negligibly. The nanodiffraction experiments also indicate that the strain in narrow microcrystals on 2 × 2 µm Si pillars is relaxed purely elastically, while in wider microcrystals on 5 × 5 µm Si pillars, plastic relaxation by means of dislocations sets in. This confirms previous work on these structures using transmission electron microscopy and defect etching.

Scanning X-ray nanodiffraction from ferroelectric domains in strained K0.75Na0.25NbO3 epitaxial films grown on (110) TbScO3.

Scanning X-ray nanodiffraction on a highly periodic ferroelectric domain pattern of a strained K0.75Na0.25NbO3 epitaxial layer has been performed by using a focused X-ray beam of about 100 nm probe size. A 90°-rotated domain variant which is aligned along [1[Formula: see text]2]TSO has been found in addition to the predominant domain variant where the domains are aligned along the [[Formula: see text]12]TSO direction of the underlying (110) TbScO3 (TSO) orthorhombic substrate. Owing to the larger elastic strain energy density, the 90°-rotated domains appear with significantly reduced probability. Furthermore, the 90°-rotated variant shows a larger vertical lattice spacing than the 0°-rotated domain variant. Calculations based on linear elasticity theory substantiate that this difference is caused by the elastic anisotropy of the K0.75Na0.25NbO3 epitaxial layer.

Nanoscale Structural Features in Major Ampullate Spider Silk.

Spider major ampullate silk is often schematically represented as a two-phase material composed of crystalline nanodomains in an amorphous matrix. Here we are interested in revealing its more complex nanoscale organization by probing Argiope bruennichi dragline-type fibers using scanning X-ray nanodiffraction. This allows resolving transversal structural features such as an about 1 μm skin layer composed of around 100 nm diameter nanofibrils serving presumably as an elastic sheath. The core consists of a composite of several nm size crystalline nanodomains with poly(l-alanine) microstructure, embedded in a polypeptide network with short-range order. Stacks of nanodomains separated by less ordered nanosegments form nanofibrils with a periodic axial density modulation which is particularly sensitive to radiation damage. The precipitation of larger β-type nanocrystallites in the outer core-shell is attributed to MaSp1 protein molecules.

Following DNA Compaction During the Cell Cycle by X-ray Nanodiffraction.

X-ray imaging of intact biological cells is emerging as a complementary method to visible light or electron microscopy. Owing to the high penetration depth and small wavelength of X-rays, it is possible to resolve subcellular structures at a resolution of a few nanometers. Here, we apply scanning X-ray nanodiffraction in combination with time-lapse bright-field microscopy to nuclei of 3T3 fibroblasts and thus relate the observed structures to specific phases in the cell division cycle. We scan the sample at a step size of 250 nm and analyze the individual diffraction patterns according to a generalized Porod's law. Thus, we obtain information on the aggregation state of the nuclear DNA at a real space resolution on the order of the step size and in parallel structural information on the order of few nanometers. We are able to distinguish nucleoli, heterochromatin, and euchromatin in the nuclei and follow the compaction and decompaction during the cell division cycle.

Lattice bending in three-dimensional Ge microcrystals studied by X-ray nanodiffraction and modelling

Extending the functionality of ubiquitous Si-based microelectronic devices often requires combining materials with different lattice parameters and thermal expansion coefficients. In this paper, scanning X-ray nanodiffraction is used to map the lattice bending produced by thermal strain relaxation in heteroepitaxial Ge microcrystals of various heights grown on high aspect ratio Si pillars. The local crystal lattice tilt and curvature are obtained from experimental three-dimensional reciprocal space maps and compared with diffraction patterns simulated by means of the finite element method. The simulations are in good agreement with the experimental data for various positions of the focused X-ray beam inside a Ge microcrystal. Both experiment and simulations reveal that the crystal lattice bending induced by thermal strain relaxation vanishes with increasing Ge crystal height.

On radiation damage in FIB-prepared softwood samples measured by scanning X-ray diffraction.

The high flux density encountered in scanning X-ray nanodiffraction experiments can lead to severe radiation damage to biological samples. However, this technique is a suitable tool for investigating samples to high spatial resolution. The layered cell wall structure of softwood tracheids is an interesting system which has been extensively studied using this method. The tracheid cell has a complex geometry, which requires the sample to be prepared by cutting it perpendicularly to the cell wall axis. Focused ion beam (FIB) milling in combination with scanning electron microscopy allows precise alignment and cutting without splintering. Here, results of a scanning X-ray diffraction experiment performed on a biological sample prepared with a focused ion beam of gallium atoms are reported for the first time. It is shown that samples prepared and measured in this way suffer from the incorporation of gallium atoms up to a surprisingly large depth of 1 µm.

Cellular Diffraction: Scanning X-Ray Nanodiffraction from Living Cells

Cellular diffraction, or scanning x-ray nanodiffraction applied to cells, is a new technique that promises insight into cellular organization at length scales of 1–200 nm, covering the features of molecules and organelles. Filling a niche between the length scales probed by optical and electron microscopy, cellular diffraction rasters a nanofocused x-ray beam across living cells in an aqueous medium and records a two-dimensional image of, for instance, the small-angle scattering signal at each position. This results in a real-space image of the cell where the contrast is based on the average intensity of the small-angle x-ray scattering (SAXS) signal (dark-field image), or phase contrast, or other modalities such as the x-ray fluorescence intensity, with spatial resolution determined by the step-size of the raster scan ranging from submicron to a few microns. But the individual diffraction patterns can also be analyzed, providing higher-resolution limited by the signal/noise of the scattering pattern, currently ∼6 nm. With the cells bound to a solid support, the SAXS patterns do not result from isotropic averaging of the scatterers, and no staining or labeling is required for the technique. The development of cellular diffraction is spearheaded by two groups from the Institute for X-Ray Physics at the University of Gottingen, led by Sarah Koster and Tim Salditt, who exploit recent advances in x-ray detectors, x-ray optics, and microfluidics in order to apply scanning SAXS imaging (1) to hydrated, living cells and address subcellular dimensions. In a collaborative first effort at beamline ID13 of the European Synchrotron Radiation Facility, they imaged freeze-dried epithelial cells and saw distinctive scattering from the network of keratin fibers in the cell (2). More recent work using a specially developed instrument and beamline P10 of PETRA III imaged both fixed and live cells. The Koster team, together with collaborators from the European Synchrotron Radiation Facility, HASYLAB, and Ghent University, observed that the azimuthally averaged SAXS signal from the cells follows a power-law decay, with different exponents for living and fixed cells (3). Moreover, the scattering decays more rapidly after repeated exposure, so the value of the exponent serves as a diagnostic for beam damage in the sample. This issue of the Biophysical Journal contains a report from the Salditt team and collaborators from the Max Planck Institute for Dynamics and Self-Organization about their studies on living and fixed amoeboid cells (4), one which provides the best realization yet of the full potential of this exciting new technique. Chemotaxis in amoeboids is accomplished by extending pseudopods with controlled polymerization of actin fibers and the retraction of receding edges by depolymerization of actin and contraction of myosin motor proteins, but the details of the actin networks remain unknown. The molecular signature of this mechanism is revealed by cellular diffraction, which shows highly anisotropic scattering streaks resulting from oriented fiber bundles in the periphery of the cell. Using an automated algorithm to convert this anisotropy to a contrast neatly outlines the advancing edges of the cell. Further modeling of the scattering streaks is necessary to characterize quantitatively the nature of the fiber bundles that give rise to the SAXS signal, but the richness of the data should allow the extraction of meaningful parameters such as the number of fibers in the bundle, their spacing, and the density of cross-links. The authors note that their data and instrument are both complementary to and compatible with x-ray coherent diffraction imaging, so that with suitable modifications, users could first apply coherent diffraction imaging to image the whole cell and then scanning nanodiffraction to examine particular regions in greater detail. Indeed, the team has already demonstrated this approach by examining freeze-dried bacterial cells with both ptychography and cellular diffraction at the coherent SAXS beamline of the Swiss Light Source (5). With the synchrotron community preparing for fourth-generation facilities that approach the diffraction limit, which will greatly improve the coherence of the x-ray beam and the ability to focus the beam (6), cellular diffraction will surely grow in application and impact.

Dislocation engineering in SiGe on periodic and aperiodic Si(001) templates studied by fast scanning X-ray nanodiffraction

Fast-scanning X-ray nanodiffraction microscopy is used to directly visualize the misfit dislocation network in a SiGe film deposited on a pit-patterned Si substrate at the beginning of plastic relaxation. X-ray real-space diffracted intensity maps are compared to topographic atomic force microscopy images, in which crosshatch lines can be seen. The change in intensity distribution as a function of the incidence angle shows localized variations in strain within the SiGe film. These variations, which reflect the order imposed by the substrate pattern, are attributed to the presence of both bunches of misfit dislocations and defect-free regions.

Perfect crystals grown from imperfect interfaces

The fabrication of advanced devices increasingly requires materials with different properties to be combined in the form of monolithic heterostructures. In practice this means growing epitaxial semiconductor layers on substrates often greatly differing in lattice parameters and thermal expansion coefficients. With increasing layer thickness the relaxation of misfit and thermal strains may cause dislocations, substrate bowing and even layer cracking. Minimizing these drawbacks is therefore essential for heterostructures based on thick layers to be of any use for device fabrication. Here we prove by scanning X-ray nanodiffraction that mismatched Ge crystals epitaxially grown on deeply patterned Si substrates evolve into perfect structures away from the heavily dislocated interface. We show that relaxing thermal and misfit strains result just in lattice bending and tiny crystal tilts. We may thus expect a new concept in which continuous layers are replaced by quasi-continuous crystal arrays to lead to dramatically improved physical properties.

Scanning X-ray nanodiffraction: from the experimental approach towards spatially resolved scattering simulations

An enhancement on the method of X-ray diffraction simulations for applications using nanofocused hard X-ray beams is presented. We combine finite element method, kinematical scattering calculations, and a spot profile of the X-ray beam to simulate the diffraction of definite parts of semiconductor nanostructures. The spot profile could be acquired experimentally by X-ray ptychography. Simulation results are discussed and compared with corresponding X-ray nanodiffraction experiments on single SiGe dots and dot molecules.

Phase Separation in Electron Doped Iron-Selenide K0.8Fe1.6Se2 Superconductor by Scanning X-ray Nano-Diffraction

A new family of high temperature superconductors, the heavily electron doped iron-selenides, like K0.8Fe1.6Se2, has been attracting high interest since they show both 30 K superconductivity, with missing hole pockets questioning the s± pairing model, and unusually high magnetic moments. The hot debate is between coexistence versus phase separation and on the possible divergence of surface from bulk structure. Here, we provide direct evidence for a nanoscale phase separation in a single crystal of K0.8Fe1.6Se2, where a first magnetic phase, with superlattice modulation $(\sqrt{5}\times\sqrt{5})$ , coexists with a second nonmagnetic phase, with a second superlattice modulation ( $\sqrt{2} \times\sqrt{2}$ ), below 520 K using transmission X-ray diffraction. The mapping of the spatial distribution of the two phases is measured by scanning X-ray nanodiffraction using a 300×300 nm2 X-ray spot. The complex spatial phase separation clarifies the coexistence of superconductivity and magnetism in the same sample.