Simultaneous Bright- and Dark-Field X-ray Microscopy at X-ray Free Electron Lasers

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

Facile Biosynthesis and Antioxidant Property of Nanogold-Cellulose Fiber Composite

Direct synthesis of gold nanoparticles (AuNPs) on cellulose fiber has been successfully performed via facile green approach using lignin-containing unbleached kraft softwood pulp. The resulting AuNPs composited fibers showed apparent color change from pale yellow to purplish-dark brown by varying the amount of gold ions (Au3+) due to the surface plasmon resonance of nanogold. Further confirmation of AuNP formation on the fiber surface was conducted by UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). X-ray photoelectron spectroscopy (XPS) analysis revealed that gold nanoparticles formed on the fiber are well-defined pure metallic gold, indicating that Au3+ ions are efficiently bioreduced into Au0 and bind to the fiber surface. Antioxidant activity was evaluated by decomposition of 2,2-diphenyl-1-picryl-hydrazyl (DPPH) in dark and light condition. As-prepared unbleached kraft fiber-AuNP composite showed significantly enhanced antioxidant activity and its DPPH scavenging rate reached about 86.05%