Dichroic coherent diffractive imaging

Abstract

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...

Soft X-ray spectromicroscopy using ptychography with randomly phased illumination

“…At X-ray wavelengths, ptychography has been used to characterize the focusing properties of X-ray optics [4][5][6] , to image interconnects within microchips 7 and to image yeast cells 8 . X-ray ptychography has recently been demonstrated using soft X-rays 9,10 , and has been used with polarized illumination to generate dichroic image contrast from magnetic thin films 11 . It can also be combined with tomography to produce three-dimensional reconstructions [12][13][14] .…”

Coherent Resonant Soft X-ray Scattering Study of Magnetic Textures in FeGe

“…Moreover, a topological winding number of the magnetically ordered system can be directly determined from the polarization-dependent (or dichroic) soft X-ray diffraction pattern alone [16]. Dichroic resonant soft X-ray scattering can be successfully combined with coherent diffraction approaches such as iterative phase retrieval [17][18][19], Fourier transform holography-based methods [20][21][22][23], and ptychography [24,25] for the lensless real-space imaging of local magnetic moment at the scale from a few tens of nanometers to a few microns. Lensless approaches allow the use of various sample environments, which confers a significant advantage compared to zone-plate-based magnetic transmission X-ray microscopy.…”

Full field tabletop EUV coherent diffractive imaging in a transmission geometry

“…This is in contrast to conventional EUV/X-ray microscopy using Fresnel zone plates (FZP), in which the resolution is limited by the width of the outermost zone. To date, CDI has been used to extract the structure and dynamics of a variety of objects, including biological samples [5,23], magnetic materials [24,25], strain fields inside a nanocrystal [26] and integrated circuits [27]. The first X-ray demonstration of CDI was at a synchrotron source in 1999 [2].…”