[en] Diffraction tomography allows us to obtain high-resolution 3-D phase and amplitude reconstructions of thick specimens. Here we report on some difficulties arising in the experimental realization of diffraction tomography. These initial experiments together with computer simulations are presented and first results obtained by incorporating the suggested modifications are shown for a collection of 1 μm diameter latex spheres and a 3 μm diameter gold dot. (authors)

[en] Driven by the requirements of new x-ray microscopy instrumentation the Stony Brook microscopy beamline X-1A has undergone considerable evolution. The room temperature scanning transmission X-ray microscope (STXM) has been completely redesigned improving performance, case of use and compatibility with other experiments. We present the highlights of the new design, the available detectors and the result of early tests of this new microscope

[en] Coherent X-ray diffraction microscopy is a method of imaging non-periodic isolated objects at resolutions only limited, in principle, by the largest scattering angles recorded. We demonstrate X-ray diffraction imaging with high resolution in all three dimensions, as determined by a quantitative analysis of the reconstructed volume images. These images are retrieved from the 3D diffraction data using no a priori knowledge about the shape or composition of the object, which has never before been demonstrated on a non-periodic object. We also construct 2D images of thick objects with infinite depth of focus (without loss of transverse spatial resolution). These methods can be used to image biological and materials science samples at high resolution using X-ray undulator radiation, and establishes the techniques to be used in atomic-resolution ultrafast imaging at X-ray free-electron laser sources

[en] We report the development of a novel experimental chamber for experiments in soft x-ray diffraction tomography, diffraction imaging of single biological objects, and magnetic speckle imaging. The chamber will allow for acquisition of nearly full three-dimensional diffraction data sets as well as high magnification zone plate images of holograms for the diffraction tomography experiment. (authors)

[en] Pr_1-xCa_xMnO₃ in the doping range between 0.3≤x≤0.5 represent an extremely interesting manganite system for the study of the interplay of different kinds of ordering (charge, orbital, lattice and spin) and the related drastic changes of the transport properties. TEM reveals the presence of electronic and structural phase separation in the chemically homogeneous material between a Zener polaron orbital and charge ordered and disordered phase in a broad temperature and doping regime. The Zener polaron (ZP) type ordering is additionally confirmed by atomic resolution EELS measurements. The ratio of the ZP ordered and disordered phases strongly depend on temperature. The ZP-ordered phase is multiferroic, showing antiferromagnetic order and weak ferroelectric polarisation due to a non-centrosymmetric distortion of the MnO6 octahedra involved in the ZP. In-situ TEM imaging with applied electric currents, we show that local ZP- and charge-ordered domains can be set into motion, be dissolved and reformed by an electric current. This represents a common mechanism for the resistance change at low and room temperatures. In addition, the CMR effect will be analyzed in the background of the determined ordered structure

[en] The Fourier inversion of phased coherent diffraction patterns offers images without the resolution and depth-of-focus limitations of lens-based tomographic systems. We report on our recent experimental images inverted using recent developments in phase retrieval algorithms, and summarize efforts that led to these accomplishments. These include ab-initio reconstruction of a two-dimensional test pattern, infinite depth of focus image of a thick object, and its high-resolution (∼10 nm resolution) three-dimensional image. Developments on the structural imaging of low density aerogel samples are discussed

[en] Recent activities in scanning transmission x-ray microscopy at Stony Brook are outlined

[en] X-ray tomography at sub-50 nm resolution of small areas (∼15 μmx15 μm) are routinely performed with both laboratory and synchrotron sources. Optics and detectors for laboratory systems have been optimized to approach the theoretical efficiency limit. Limited by the availability of relatively low-brightness laboratory X-ray sources, exposure times for 3-D data sets at 50 nm resolution are still many hours up to a full day. However, for bright synchrotron sources, the use of these optimized imaging systems results in extremely short exposure times, approaching live-camera speeds at the Advanced Photon Source at Argonne National Laboratory near Chicago in the US These speeds make it possible to acquire a full tomographic dataset at 50 nm resolution in less than a minute of true X-ray exposure time. However, limits in the control and positioning system lead to large overhead that results in typical exposure times of ∼15 min currently.We present our work on the reduction and elimination of system overhead and toward complete automation of the data acquisition process. The enhancements underway are primarily to boost the scanning rate, sample positioning speed, and illumination homogeneity to performance levels necessary for unattended tomography of large areas (many mm² in size). We present first results on this ongoing project.

[en] Clay-rich low-organic carbon formations (e.g., Callovo-Oxfordian argillite in France and Opalinus Clay in Switzerland) are considered as host rocks for radioactive waste disposal. The clay-organic carbon has a strong impact on the chemical stability of the clays. For this reason, the nature of the clay-organic carbon, the release of hydrophilic organic compounds, namely, humic (HA) and fulvic acids (FA) and the radiation sensitivity of the undisturbed host rock organics was investigated. The clay sample originates from Oxfordian argillite (447 m depth, borehole EST 104). HA and FA were extracted following the standard International Humic Substance Society (IHSS) isolation procedure. Synchrotron based (C-, K-, Ca-, O- and Fe-edge XANES) scanning transmission X-ray microscopy (STXM) and FT-IR microspectroscopy was used to identify under high spatial resolution the distribution of clay-organic matter with different functionality using principal component and cluster analysis. The results show that in this old (Jurassic) geological formation, small parts of the organic inventory (1-5%) keeps the structure/functionality and can be mobilized as hydrophilic humic substance type material (HA and FA). Target spectra analysis shows best correlation for isolated humic acids with organics found in smectite-rich regions, whereas the extractable FA has better spectral similarities with the illite mixed layer minerals (MLM) regions. After radiation of 1.7 GGy under helium atmosphere the same rock sample area was investigated for radiation damage. Radiation damage in the smectite and illite-MLM associated organic matter is comparably low with 20-30% total oxygen mass loss and 13-18% total carbon mass loss. A critical dose d_c of 2.5 GGy and a optical density after infinite radiation (OD_∝) of 54% was calculated under room temperature conditions. C(1s) XANES show a clear increase in C=C bonds especially in the illite-MLM associated organics. This results suggests a combination of the formation of C=C bond due to crosslinking via polymerization and mass loss due to bond breaking (scissioning) in the main chain or in side groups of the organic macromolecules upon irradiation.

[en] A dedicated in-vacuum coherent x-ray diffraction microscope was installed at the 2-ID-B beamline of the Advanced Photon Source for use with 0.7-2.9 keV x-rays. The instrument can accommodate three common implementations of diffractive imaging; plane wave illumination; defocused-probe (Fresnel diffractive imaging) and scanning (ptychography) using either a pinhole, focused or defocused probe. The microscope design includes active feedback to limit motion of the optics with respect to the sample. Upper bounds on the relative optics-to-sample displacement have been measured to be 5.8 nm(v) and 4.4 nm(h) rms/h using capacitance micrometry and 27 nm/h using x-ray point projection imaging. The stability of the measurement platform and in-vacuum operation allows for long exposure times, high signal-to-noise and large dynamic range two-dimensional intensity measurements to be acquired. Finally, we illustrate the microscope's stability with a recent experimental result.