A high density of oxygen vacancies has been found in an experiment to determine the path of electrical conduction in Cr-doped SrTiO3 memory cells. The Cr acts as a seed for the localization of oxygen vacancies, leading to a statistically homogeneous distribution of charge carriers within the path. This warrants a controllable doping profile and improved device scaling down to the nanometer scale. The combination of laterally resolved micro-X-ray absorption spectroscopy and thermal imaging concludes that the resistance switching in Cr-doped SrTiO3 originates from an oxygen-vacancy drift to/from the electrode that was used as anode during the conditioning process. The experiments shows that this oxygen vacancy concept is crucial for the entire class of transition-metal-oxide-based bipolar resistance-change memory.

Role of Oxygen Vacancies in Cr‐Doped SrTiO3 for Resistance‐Change Memory

TiO2 particles are commonly used as dietary supplements and may contain up to 36% of nano-sized particles (TiO2-NPs). Still impact and translocation of NPs through the gut epithelium is poorly documented. We show that, in vivo and ex vivo, agglomerates of TiO2-NPs cross both the regular ileum epithelium and the follicle-associated epithelium (FAE) and alter the paracellular permeability of the ileum and colon epithelia. In vitro, they accumulate in M-cells and mucus-secreting cells, much less in enterocytes. They do not cause overt cytotoxicity or apoptosis. They translocate through a model of FAE only, but induce tight junctions remodeling in the regular ileum epithelium, which is a sign of integrity alteration and suggests paracellular passage of NPs. Finally we prove that TiO2-NPs do not dissolve when sequestered up to 24 h in gut cells. Taken together these data prove that TiO2-NPs would possibly translocate through both the regular epithelium lining the ileum and through Peyer’s patches, would induce epithelium impairment, and would persist in gut cells where they would possibly induce chronic damage.

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Titanium dioxide nanoparticle impact and translocation through ex vivo, in vivo and in vitro gut epithelia.

Spectroscopic approaches to plant and soil sciences have provided important information for several decades. However, many of these approaches suffered from a number of limitations and drawbacks especially in terms of spatial resolution and requirements for sample preparation. The advent of dedicated synchrotron facilities, that allow the exploitation of the particular qualities of synchrotron radiation as a research tool, has revolutionised the way we approach the investigation of nutrients and contaminants in environmental samples. Various synchrotron-based techniques are currently available that permit such investigations in situ and at the molecular level. The continuous development of these techniques is delivering substantial gains in terms of sensitivity and spatial resolution which allows analyses of diluted samples at the sub-micron scale. This paper aims at providing an introduction to synchrotron radiation and to the fundamentals of some widely used synchrotron-based techniques, in particular X-ray absorption, fluorescence and tomography. Furthermore, examples are provided regarding the applications of synchrotron-based techniques in the field of plant, soil and rhizosphere research. Finally, current limitations and future perspectives of synchrotron techniques are discussed.

Synchrotron-based techniques for plant and soil science: opportunities, challenges and future perspectives

Effect of phosphate, silicate, and Ca on Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water studied by X-ray absorption spectroscopy.

The degree of substitution of Si4+ by Al3+ in the oxygen-terminated tetrahedra (Al T-sites) of zeolites determines the concentration of ion-exchange and Bronsted acid sites. Because the location of the tetrahedra and the associated subtle variations in bond angles influence the acid strength, quantitative information about Al T-sites in the framework is critical to rationalize catalytic properties and to design new catalysts. A quantitative analysis is reported that uses a combination of extended X-ray absorption fine structure (EXAFS) analysis and 27Al MAS NMR spectroscopy supported by DFT-based molecular dynamics simulations. To discriminate individual Al atoms, sets of ab initio EXAFS spectra for various T-sites are generated from DFT-based molecular dynamics simulations, allowing quantitative treatment of the EXAFS single- and multiple-photoelectron scattering processes out to 3–4 atom shells surrounding the Al absorption center. It is observed that identical zeolite types show dramatically different ...

Quantitatively Probing the Al Distribution in Zeolites

The beamline “LUCIA” (line for ultimate characterization by imaging and absorption) is a “tender” (0.8–8 keV) X-ray microprobe with capabilities for chemical speciation by micro-X-ray absorption spectroscopy (μ-XAS) and for elemental mapping by X-ray micro-fluorescence (μ-XRF). It allows the possibility to study heterogeneous samples at a micrometer scale and to combine these two element-specific and non-destructive techniques. A monochromatic beam of a few micrometer in size is incident on a sample which is mounted on a scanning x–y–z stage. μ-XRF shows the location of the elements, their relative abundances, and their association with other elements. One can take advantage of the monochromatic beam which allows separating out different elements by their absorption edges. After mapping the fluorescence, spots of interest can be analysed by XAS to determine the speciation (local chemistry, quantitative determination of the local geometric structure around the absorbing atom) of the elements and how they depend on the different components. Installed at first at the SLS of the Paul Scherrer Institute (Switzerland), the LUCIA beamline will be transferred to SOLEIL by the beginning of 2008. The energy range offered by the beamline corresponds to the best performances of SLS and SOLEIL in terms of brightness. It allows XAS experiments at the K edge of elements ranging from Na to Fe, L edges from Ni to Gd, and M edges of rare earths and actinides.

LUCIA, a microfocus soft XAS beamline

ANATOMIX is a 200-m-long undulator beamline for full-field tomography techniques at photon energies from 5 to 25 keV. It is currently under construction at Synchrotron SOLEIL, the French national light source near Paris. ANATOMIX will feature experimental stations both for parallel-beam microtomography (with a beam of up to 40 mm width) and for zone-plate transmission X-ray microscopy (down to pixel sizes of 30 nm) in absorption and phase contrast. The location of ANATOMIX on a canted straight section of the SOLEIL storage ring implies specific challenges for the design and operation conditions of the beamline. In this paper we present general design aspects and the status of construction.

https://robots.iopscience.iop.org/article/10.1088/1742-6596/849/1/012037/pdf

The tomography beamline ANATOMIX at Synchrotron SOLEIL

We present what we believe to be the first automatic alignment of a synchrotron beamline by the Hartmann technique. Experiments were performed, in the soft-x-ray range (E=3 keV, lambda=0.414 nm), by using a four-actuator Kirkpatrick-Baez (KB) active optic. A system imaging the KB focal spot and a soft-x-ray Hartmann wavefront sensor were used alternatively to control the KB optic. The beam corrected with the help of the imaging system was used to calibrate the wavefront sensor. With both closed loops, we focused the beam into a 6.8 µm×9 µm FWHM focal spot.

Automatic alignment of a Kirkpatrick-Baez active optic by use of a soft-x-ray Hartmann wavefront sensor.

X-ray imaging of plasmas with a resolution on the order of 1 μm could not be achieved with pinholes because the light flux on the detector would be too low. We tested two different types of diffractive lenses derived from the circular grating based on the Fresnel zones. Compared to pinholes, they can have an equivalent diameter of about 100 μm with a resolution of about 1 μm. The two kinds of devices tested were: (1) a transmission phase Fresnel zone lens (PFZL) associated with a multilayer mirror; (2) a reflective Bragg–Fresnel lens (BFL) which combines a multilayer mirror and the grating. The PFZL works at normal incidence by transmission; an additional mirror is used to reflect only a small bandwidth within the spectrum; the angle of reflection of the multilayer of the imaging beam on the mirror is set as to adjust the center of the useful bandwidth. The BFL works at fixed grazing incidence and we only use an off-axis part of the BFL in order to avoid the illumination of the detector by zeroth order di...

Imaging of laser produced plasma at 1.43 keV using Fresnel zone plate and Bragg–Fresnel lens

In 2002, first experiments at the Advanced Light Source (ALS) at Berkeley, allowed us to test a first prototype of EUV Hartmann wave-front sensor. Wave-front measurements were performed over a wide wavelength range from 7 to 25 nm. Accuracy of the sensor was proved to be better than λEUV/120 rms (λEUV = 13.4 nm, about 0.1 nm accuracy) with sensitivity exceeding λEUV/600 rms, demonstrating the high metrological performances of this system.
At the Swiss Light Source (SLS), we succeeded recently in the automatic alignment of a synchrotron beamline by Hartmann technique. Experiments were performed, in the hard X-ray range (E = 3 keV, λ = 0.414 nm), using a 4-actuators Kirkpatrick-Baez (KB) active optic. An imaging system of the KB focal spot and a hard X-ray Hartmann wave-front sensor were used alternatively to control the KB. The imaging system used a genetic algorithm to achieve the highest energy in the smallest spot size, while the wave-front sensor used the KB influence functions to achieve the smallest phase distortions in the incoming beam. The corrected beam achieved with help of the imaging system was used to calibrate the wave-front sensor. With both closed loops, we focused the beam into a 6.8x9 μm2 FWHM focal spot. These results are limited by the optical quality of the imaging system.

Gilles Cauchon

Papers

LUCIA, a microfocus soft XAS beamline

The tomography beamline ANATOMIX at Synchrotron SOLEIL

Automatic alignment of a Kirkpatrick-Baez active optic by use of a soft-x-ray Hartmann wavefront sensor.

Imaging of laser produced plasma at 1.43 keV using Fresnel zone plate and Bragg–Fresnel lens

X-ray beam metrology and x-ray optic alignment by Hartmann wavefront sensing