72 research outputs found
Water Window Ptychographic Imaging with Characterized Coherent X-rays
We report on a ptychographical coherent diffractive imaging experiment in the
water window with focused soft X-rays at . An X-ray beam with
high degree of coherence was selected for ptychography at the P04 beamline of
the PETRA III synchrotron radiation source. We measured the beam coherence with
the newly developed non-redundant array method. A pinhole
in size selected the coherent part of the beam and was used for ptychographic
measurements of a lithographically manufactured test sample and fossil diatom.
The achieved resolution was for the test sample and only
limited by the size of the detector. The diatom was imaged at a resolution
better than .Comment: 22 pages. 7 figure
Local structure of semicrystalline P3HT films probed by nanofocused coherent x-rays
We present results of an x-ray study of structural properties of
semicrystalline polymer films using nanofocused x-ray beam. We applied the
x-ray cross-correlation analysis (XCCA) to scattering data from blends of
poly(3-hexylthiophene) (P3HT) embedded with gold nanoparticles (AuNPs).
Spatially resolved maps of orientational distribution of crystalline domains
allow us to distinguish sample regions of predominant face-on morphology,with a
continuous transition to edge-on morphology. The average size of crystalline
domains was determined to be of the order of 10 nm. As compared to pristine
P3HT film, the P3HT/AuNPs blend is characterized by substantial ordering of
crystalline domains, which can be induced by Au nanoparticles. The
inhomogeneous structure of the polymer film is clearly visualized on the
spatially resolved nanoscale 2D maps obtained using XCCA. Our results suggest
that the observed changes of the polymer matrix within crystalline regions can
be attributed to nanoconfinement in the presence of gold nanoparticles.Comment: 10 pages, 6 figures, 53 reference
Disorder Dynamics in Battery Nanoparticles During Phase Transitions Revealed by Operando Single-Particle Diffraction
Structural and ion-ordering phase transitions limit the viability of
sodium-ion intercalation materials in grid scale battery storage by reducing
their lifetime. However, the combination of phenomena in nanoparticulate
electrodes creates complex behavior that is difficult to investigate,
especially on the single nanoparticle scale under operating conditions. In this
work, operando single-particle x-ray diffraction (oSP-XRD) is used to observe
single-particle rotation, interlayer spacing, and layer misorientation in a
functional sodium-ion battery. oSP-XRD is applied to
Na[NiMn]O, an archetypal P2-type sodium-ion
positive electrode material with the notorious P2-O2 phase transition induced
by sodium (de)intercalation. It is found that during sodium extraction, the
misorientation of crystalline layers inside individual particles increases
before the layers suddenly align just prior to the P2-O2 transition. The
increase in the long-range order coincides with an additional voltage plateau
signifying a phase transition prior to the P2-O2 transition. To explain the
layer alignment, a model for the phase evolution is proposed that includes a
transition from localized to correlated Jahn-Teller distortions. The model is
anticipated to guide further characterization and engineering of sodium-ion
intercalation materials with P2-O2 type transitions. oSP-XRD therefore opens a
powerful avenue for revealing complex phase behavior in heterogeneous
nanoparticulate systems.Comment: 23 pages, 4 main figures, 9 supplemental figure
Quantum Imaging with Incoherently Scattered Light from a Free-Electron Laser
The advent of accelerator-driven free-electron lasers (FEL) has opened new
avenues for high-resolution structure determination via diffraction methods
that go far beyond conventional x-ray crystallography methods. These techniques
rely on coherent scattering processes that require the maintenance of
first-order coherence of the radiation field throughout the imaging procedure.
Here we show that higher-order degrees of coherence, displayed in the intensity
correlations of incoherently scattered x-rays from an FEL, can be used to image
two-dimensional objects with a spatial resolution close to or even below the
Abbe limit. This constitutes a new approach towards structure determination
based on incoherent processes, including Compton scattering, fluorescence
emission or wavefront distortions, generally considered detrimental for imaging
applications. Our method is an extension of the landmark intensity correlation
measurements of Hanbury Brown and Twiss to higher than second-order paving the
way towards determination of structure and dynamics of matter in regimes where
coherent imaging methods have intrinsic limitations
Real-space imaging of polar and elastic nano-textures in thin films via inversion of diffraction data
Exploiting the emerging nanoscale periodicities in epitaxial, single-crystal
thin films is an exciting direction in quantum materials science: confinement
and periodic distortions induce novel properties. The structural motifs of
interest are ferroelastic, ferroelectric, multiferroic, and, more recently,
topologically protected magnetization and polarization textures. A critical
step towards heterostructure engineering is understanding their nanoscale
structure, best achieved through real-space imaging. X-ray Bragg coherent
diffractive imaging visualizes sub-picometer crystalline displacements with
tens of nanometers spatial resolution. Yet, it is limited to objects spatially
confined in all three dimensions and requires highly coherent, laser-like
x-rays. Here we lift the confinement restriction by developing real-space
imaging of periodic lattice distortions: we combine an iterative phase
retrieval algorithm with unsupervised machine learning to invert the diffuse
scattering in conventional x-ray reciprocal-space mapping into real-space
images of polar and elastic textures in thin epitaxial films. We first
demonstrate our imaging in PbTiO3/SrTiO3 superlattices to be consistent with
published phase-field model calculations. We then visualize strain-induced
ferroelastic domains emerging during the metal-insulator transition in Ca2RuO4
thin films. Instead of homogeneously transforming into a low-temperature
structure (like in bulk), the strained Mott insulator splits into nanodomains
with alternating lattice constants, as confirmed by cryogenic scanning
transmission electron microscopy. Our study reveals the type, size,
orientation, and crystal displacement field of the nano-textures. The
non-destructive imaging of textures promises to improve models for their
dynamics and enable advances in quantum materials and microelectronics
Coherent Methods in X-Ray Scattering
X-ray radiation has been used to study structural properties of materials for morethan a hundred years. Construction of extremely coherent and bright X-ray radiationsources such as free electron lasers (FELs) and latest generation storage rings led torapid development of experimental methods relying on high radiation coherence.These methods allow to perform revolutionary studies in a wide range of fields fromsolid state physics to biology. In this thesis I focus on several important problemsconnected with the coherent methods.The first part considers applications of dynamical diffraction theory on crystals tostudies with coherent X-ray radiation. It presents the design of a high-resolution spectrometerfor free electron lasers that should allow to resolve spectral structure of individualFEL pulses. The spectrometer is based on the principle of dynamical diffractionfocusing. The knowledge of individual FEL pulse spectra is necessary for understandingFEL longitudinal coherence. In the same part I present quasi-kinematicalapproximation to dynamical theory which allows to treat analytically phase effectsobserved in X-ray coherent imaging on nanocrystals. These effects may play a bigrole when methods such as ptychography are used to study crystalline samples.The second part deals with measurements of FEL coherence properties using intensity- intensity interferometry. Results of several experiments performed at FELsFLASH and LCLS are revealed in this section. I have developed models and theoriesto explain the behavior observed in experiments on FLASH. These models allowedto extract information about external positional jitter of FEL pulses and secondarybeams present in FEL radiation. In the LCLS experiment the Hanbury Brown andTwiss type interferometry was performed on Bragg peaks from colloidal crystal. Thisdid not require additional measurements without the sample and information wasextracted directly from diffraction patterns. Therefore intensity-intensity interferometrycan in principle be used directly on sample diffraction patterns to understandstatistical behavior of the FEL during the measurements.Another problem that is considered in this thesis is the problem of electronic damagefrom bright FEL pulses. I have considered the effect of many ionization processeson single-particle imaging experiments on biological objects. Simulations were performedto understand the effect of shortening pulse durations and increasing intensitieson the diffraction pattern, its fluctuations from pulse to pulse and Comptonbackground. As a result of these simulations, bounds on the feasible intensities andpulse durations are suggested
- …