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

LURE‐SOLEIL (France) and the Swiss Light Source (SLS) are building together a new micro focused beamline for micro x‐ray absorption spectroscopy and micro imaging. This line is designed to deliver a photon flux of the order of 1012 ph/sec on a 1 × 1 μm spot within the energy domain of 0.8 to 7 keV. This beam line is being installed on the X07M straight section of SLS. The source is an APPLE II undulator with a period of 54 mm. The main advantage of this device lies in the delivery of any degree of polarization, linear or circular, over the whole energy range, without the need of a sample‐position change. The monochromator will be a fixed exit double crystal equipped with 5 sets of crystals, thanks to the very narrow photon beam from the undulator ( Beryl, KTP, YB66, InSb(111), Si(111) ). The optics includes a first horizontal focusing mirror (spherical), which produces an intermediate source for the horizontal mirror of a Kirkpatrick‐Baez (KB) system. The vertical mirror of the KB directly images the source. Finally, a low‐pass double mirror filter insures a proper harmonic rejection.

LUCIA — a new 1-7 keV μ-XAS Beamline

The DiffAbs beamline, the Detectors and the Design and Engineering groups at Synchrotron SOLEIL, in collaboration with ImXPAD and Cegitek companies, have developed an original and unique detector with a circular shape. This detector is based on the hybrid pixel photon-counting technology and consists of the specific assembly of 20 hybrid pixel array detector (XPAD) modules.

https://journals.iucr.org/s/issues/2022/01/00/gy5028/gy5028.pdf

J. M. Dubuisson

Papers

LUCIA, a microfocus soft XAS beamline

LUCIA — a new 1-7 keV μ-XAS Beamline

The CirPAD, a circular 1.4 M hybrid pixel detector dedicated to X-ray diffraction measurements at Synchrotron SOLEIL