Understanding electronic structure at the nanoscale is crucial to untangling fundamental physics puzzles such as phase separation and emergent behavior in complex magnetic oxides. Probes with the ability to see beyond surfaces on nanometer length and subpicosecond time scales can greatly enhance our understanding of these systems and will undoubtedly impact development of future information technologies. Polarized X-rays are an appealing choice of probe due to their penetrating power, elemental and magnetic specificity, and high spatial resolution. The resolution of traditional X-ray microscopes is limited by the nanometer precision required to fabricate X-ray optics. Here we present a novel approach to lensless imaging of an extended magnetic nanostructure, in which a scanned series of dichroic coherent diffraction patterns is recorded and numerically inverted to map its magnetic domain configuration. Unlike holographic methods, it does not require a reference wave or precision optics. In addition, it enables the imaging of samples with arbitrarily large spatial dimensions, at a spatial resolution limited solely by the coherent X-ray flux, wavelength, and stability of the sample with respect to the beam. It can readily be extended to nonmagnetic systems that exhibit circular or linear dichroism. We demonstrate this approach by imaging ferrimagnetic labyrinthine domains in a Gd/Fe multilayer with perpendicular anisotropy and follow the evolution of the domain structure through part of its magnetization hysteresis loop. This approach is scalable to imaging with diffraction-limited resolution, a prospect rapidly becoming a reality in view of the new generation of phenomenally brilliant X-ray sources.magnetism | phase retrieval | lensless imaging | ptychography | X-ray microscopy M aterials such as magnetic multilayers and alloys, polymers, liquid crystals, biofibers, and biominerals all exhibit self-organizing, reaction-diffusion, and pattern-forming behavior not fully understood. New schemes for directed domain formation in magnetic multilayers and alloys are integral parts of next-generation magnetic data storage and spintronic technologies (1, 2). Controlled phase transitions and ordering dynamics in polymers and liquid crystals under applied electric fields, with consequent photonic bandgap shifts, play a major role in organic laser technology (3). In the biological sciences, certain biofibers display tensile properties similar to that of steel yet are far more lightweight, properties thought to be the result of self-organized phase separation of molecular crystalline and amorphous regions within the fibers (4, 5). Deeper understanding of biomineral growth and the interaction between inorganic material and organic macromolecule phases could enable use of similar techniques to fabricate novel synthetic materials.Microscopy using dichroism as a contrast mechanism can reveal much about phase ordering, separation, and coexistence in these kinds of systems. All of these materials have an order parameter that scatte...

In situ study of annealing-induced strain relaxation in diamond nanoparticles using Bragg coherent diffraction imaging APL Materials 5, 026105 (2017);

Coherent X-rays reveal defects in photonic crystals of butterfly wings.

We report on the dynamics of the structural order parameter in a chromium film using synchrotron radiation in response to photo-induced ultrafast excitations. Following transient optical excitations the effective lattice temperature of the film rises close to the Néel temperature and the charge density wave (CDW) amplitude is reduced but does not appear to ever be fully destroyed.The persistence of the CDWs diffraction signal demonstrates that the CDW, if destroyed by the laser pulse, must be reestablished within the 100-ps time resolution of the synchrotron x-ray pulses.Furthermore, at all times after photoexcitation, the CDW retains its low-temperature periodicity, rather than regenerating with its high-temperature period shortly after photoexcitation. The longterm evolution shows that the CDW reverts to its ground state on a timescale of 370±40 ps. We attribute the apparent persistence of the CDW to the long-lived periodic lattice displacement in chromium. This study highlights the fundamental role of the lattice distortion in charge ordered systems and its impact on the recondensation dynamics of the charge ordered state in strongly correlated materials.

We use coherent x-ray diffractive imaging to map the local distribution of strain in gold (Au) polyhedral nanocrystals grown on a silicon (Si) substrate by a single-step thermal chemical vapor deposition process. The lattice strain at the surface of the octahedral nanocrystal agrees well with the predictions of the Young-Laplace equation quantitatively, but exhibits a discrepancy near the nanocrystal-substrate interface. We attribute this discrepancy to the dissimilar interfacial energies between Au/Air and Au/Si and to the difference in thermal expansion between the nanocrystal and the substrate during the cooling process.