Nanoscale phase separation in the iron chalcogenide superconductor K0.8Fe1.6Se2 as seen via scanning nanofocused x-ray diffraction

Advanced synchrotron radiation focusing down to a size of 300 nm has been used to visualize nanoscale phase separation in the K0.8Fe1.6Se2 superconducting system using scanning nanofocus single-crystal X-ray diffraction. The results show an intrinsic phase separation in K0.8Fe1.6Se2 single crystals at T< 520 K, revealing coexistence of i) a magnetic phase characterized by an expanded lattice with superstructures due to Fe vacancy ordering and ii) a non-magnetic phase with an in-plane compressed lattice. The spatial distribution of the two phases at 300 K shows a frustrated or arrested nature of the phase separation. The space-resolved imaging of the phase separation permitted us to provide a direct evidence of nanophase domains smaller than 300 nm and different micrometer-sized regions with percolating magnetic or nonmagnetic domains forming a multiscale complex network of the two phases.Comment: 5 pages, 4 figure

Strain in a silicon-on-insulator nanostructure revealed by 3D x-ray Bragg ptychography

International audienceProgresses in the design of well-defined electronic band structure and dedicated functionalities rely on the high control of complex architectural device nano-scaled structures. This includes the challenging accurate description of strain fields in crystalline structures, which requires non invasive and three-dimensional (3D) imaging methods. Here, we demonstrate in details how x-ray Bragg ptychography can be used to quantify in 3D a displacement field in a lithographically patterned silicon-on-insulator structure. The image of the crystalline properties, which results from the phase retrieval of a coherent intensity data set, is obtained from a well-controlled optimized process, for which all steps are detailed. These results confirm the promising perspectives of 3D Bragg ptychography for the investigation of complex nano-structured crystals in material science

Effects on collagen orientation in the cornea after trephine injury

Purpose: Structural changes are well known to occur in the cornea after injury. The aim of this study was to investigate collagen orientation changes in the cornea during a short-term wound healing process. Methods: Seven bovine corneas were injured using a penetrating 5 mm biopsy punch and were subsequently organ cultured for up to two weeks. Six uninjured corneas acted as controls. The trephine wounded samples were snap frozen in liquid nitrogen either immediately after injury (0 h) or after 1 or 2 weeks in culture. Control/uninjured samples were snap frozen on arrival (0 h) or after 1 or 2 weeks in culture. Wide angle X-ray diffraction data were collected from each cornea at the UK Synchrotron Radiation Source or at the European Synchrotron Radiation Facility. Data analysis revealed information about collagen orientation and distribution in the corneal stroma during wound healing. For histology, two trephine wounded corneas at 0 h and 1 week and one control/uninjured cornea at 0 h were fixed in 10% neutral buffered formalin and processed for wax embedding. Wax sections were subsequently counterstained with haematoxylin and eosin to observe tissue morphology and the time course of complete re-epithelialization. Results: Immediately after injury, collagen organization was altered in a small area inside the wound but remained similar to the control/uninjured sample in the remainder of the tissue. After one week, the trephine wounded corneas showed complete re-epithelialization and evidence of swelling while collagen adopted a radial arrangement inside and outside the wound. Conclusions: Remarkable changes in collagen fibril orientation were observed in trephine wounded corneas. Orientation changes immediately after wounding are likely to be due to the mechanical deformation of the tissue during the wounding process. However, tissue swelling and changes in collagen orientation at later stages probably reflect the processes of tissue repair. These differences will determine corneal stability and strength following trauma and possibly refractive surgery

Application of Synchrotron Radiation-Based Micro-Analysis on Cadmium Yellows in Pablo Picasso's Femme

The cultural heritage community is increasingly exploring synchrotron radiation (SR) based techniques for the study of art and archaeological objects. When considering heterogeneous and complex micro-samples, such as those from paintings, the combination of different SR X-ray techniques is often exploited to overcome the intrinsic limitations and sensitivity of the single technique. Less frequently, SR X-ray analyses are combined with SR micro-photoluminescence or micro-Fourier Transform Infrared spectroscopy, which provide complementary information on the molecular composition, offering a unique integrated analysis approach. Although the spatial correlation between the maps obtained with different techniques is not straightforward due to the different volumes probed by each method, the combination of the information provides a greater understanding and insight into the paint chemistry. In this work, we discuss the advantages and disadvantages of the combination of X-ray techniques and SR-based photoluminescence through the study of two paint micro-samples taken from Pablo Picasso's Femme (1907). The painting contains two cadmium yellow paints (based on CdS): one relatively intact and one visibly degraded. SR micro-analyses demonstrated that the two Cd-yellow paints differ in terms of structure, chemical composition, and photoluminescence properties. In particular, on the basis of the combination of different SR measurements, we hypothesize that the degraded yellow is based on nanocrystalline CdS with high presence of Cd(OH)Cl. These two characteristics have enhanced the reactivity of the paint and strongly influenced its stability

Characterization of activated carbon fiber/polyaniline materials by position-resolved microbeam small-angle X-ray scattering

Activated carbon fiber (ACF)/polyaniline (PANI) materials have been prepared using two different methods, viz. chemical and electrochemical polymerization. Electrochemical characterization of both materials shows that the electrodes with polyaniline have a higher capacitance than does a pristine porous carbon electrode. To analyze the distribution of PANI within the ACF, characterization by position-resolved microbeam small-angle X-ray scattering (μSAXS) has been carried out. μSAXS results obtained with a single ACF indicate that, for the experimental conditions used, a PANI coating is formed inside the micropores and that it is higher in the external regions of the ACF than in the core. Additionally, it seems that the penetration of PANI inside the fibers occurs in a larger extent for the chemical polymerization or, in other words, for the electrochemically polymerized sample there is a slightly larger accumulation of PANI in the external regions of the ACF.Fil: Salinas-Torres, D.. Universida de Alicante; EspañaFil: Sieben, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Lozano-Castelló, D.. Universida de Alicante; EspañaFil: Morallón, E.. Universida de Alicante; EspañaFil: Burghammer, M.. EuropeanSynchrotronRadiationFacility; FranciaFil: Riekel, C.. EuropeanSynchrotronRadiationFacility; FranciaFil: Cazorla Amorós, Diego. Universida de Alicante; Españ

<i>In vivo</i> X-ray elemental imaging of single cell model organisms manipulated by laser-based optical tweezers

We report on a radically new elemental imaging approach for the analysis of biological model organisms and single cells in their natural, in vivo state. The methodology combines optical tweezers (OT) technology for non-contact, laser-based sample manipulation with synchrotron radiation confocal X-ray fluorescence (XRF) microimaging for the first time. The main objective of this work is to establish a new method for in vivo elemental imaging in a two-dimensional (2D) projection mode in free-standing biological microorganisms or single cells, present in their aqueous environment. Using the model organism Scrippsiella trochoidea, a first proof of principle experiment at beamline ID13 of the European Synchrotron Radiation Facility (ESRF) demonstrates the feasibility of the OT XRF methodology, which is applied to study mixture toxicity of Cu-Ni and Cu-Zn as a result of elevated exposure. We expect that the new OT XRF methodology will significantly contribute to the new trend of investigating microorganisms at the cellular level with added in vivo capability

SiO2 glass density to lower-mantle pressures

The convection or settling of matter in the deep Earth’s interior is mostly constrained by density variations between the different reservoirs. Knowledge of the density contrast between solid and molten silicates is thus of prime importance to understand and model the dynamic behavior of the past and present Earth. SiO2 is the main constituent of Earth’s mantle and is the reference model system for the behavior of silicate melts at high pressure. Here, we apply our recently developed x-ray absorption technique to the density of SiO2 glass up to 110 GPa, doubling the pressure range for such measurements. Our density data validate recent molecular dynamics simulations and are in good agreement with previous experimental studies conducted at lower pressure. Silica glass rapidly densifies up to 40 GPa, but the density trend then flattens to become asymptotic to the density of SiO2 minerals above 60 GPa. The density data present two discontinuities at ∼17 and ∼60  GPa that can be related to a silicon coordination increase from 4 to a mixed 5/6 coordination and from 5/6 to sixfold, respectively. SiO2 glass becomes denser than MgSiO3 glass at ∼40  GPa, and its density becomes identical to that of MgSiO3 glass above 80 GPa. Our results on SiO2 glass may suggest that a variation of SiO2 content in a basaltic or pyrolitic melt with pressure has at most a minor effect on the final melt density, and iron partitioning between the melts and residual solids is the predominant factor that controls melt buoyancy in the lowermost mantle