Some recent developments in the surface-analytical application of X-ray fluorescence spectrometry

Summary Standard depth profiles of an analyte deposited into (diffusion or ion implantation) or on (thin-film deposition) a plane surface can be analyzed for profile type and centroid depth or film thickness by means of a standardless method in which the matrix-attenuated signals of the fiuorescing analyte measured at two different take-off angles are related to the mathematical distribution moments of the profile. For a binary thin film the element ratio can also be established. Results obtained on phosphorus profiles in silicon and on zinc sulphide optical coatings are referred to.The quantity or concentration level can be determined by use of a reference standard which may contain the analyte in an entirely different distribution. This simplifies the calibration of secondary reference standards.A good lateral resolution in the sub-millimeter range can be achieved with synchrotron radiation. A further improvement of lateral resolution is possible by direct excitation with electron microbeams, though at significantly inferior detection limits.

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Neuere Entwicklungen bei der oberflächen-analytischen Anwendung der Röntgenfluorescenz-Spektrometrie

     

≪Monocristaux≫ de copolymères triséquencés styrène/isoprène/styrène présentant la structure cylindrique II. Étude de la déformation par élongation

Résumé On a étudié par diffraction des rayons X aux petits angles des monocristaux de copolymère triséquencé styréne/isopréne/styréne présentant la structure cylindrique. On a porté son attention sur la déformation structurale que subissent ces systèmes lorsqu'ils sont soumis à une contrainte d'élongation dirigée perpendiculairement à l'axe des cylindres. On a montré que le réseau cristallin se déforme réversiblement de manière parfaitement affine.

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Summary This is a low-angle X-ray diffraction study of single-crystals obtained from styrene/isoprene/styrene three-block copolymers presenting the cylindrical structure. The structural deformation has been analyzed as a function of an elongational strain applied to the samples perpendicularly to the axis of the cylinders. It has been shown that the crystal lattice deforms in a reversible and perfectly affine way.

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Zusammenfassung Mit Hilfe der Röntgenkleinwinkelstreuung haben wir die zylindrischen monokristallinen Strukturen der Polystyrol-Polyisopren-Polystyrol-BlockcopolymerenProben untersucht.Wir haben besonders die strukturelle Änderung analysiert, die auftritt, wenn eine Dehnung mit einem Zug senkrecht zur Zylinderachse angewandt wird.Es wird gezeigt, daß das Kristallgitter sich reversibel und streng affin verformt.

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Avec 5 figures et 3 tableaux     

F-to-HF reactions. IX. Nonthermal complications for the CH4/C3F6/C2F6 moderated nuclear recoil system

Results are reported from moderated nuclear recoil ¹⁸F experiments with the CH₄/C₃F₆/C₂F₆ mixture system. At a 99.5% confidence level measurement precision of ±3.4%, non-thermal F-to-HF reactions are phenomenologically suppressed at C₂F₆ moderator concentrations in the range of 95.0–99.95 mol-%. Effectively equilibrium reaction conditions can be established in well-designed experiments of this type.     

Superacids Based on Pentafluoroorthotellurate Derivatives of Aluminum

The new Lewis acid Al(OTeF₅)₃ and its acetonitrile adduct CH₃CN→Al(OTeF₅)₃ were obtained by a simple one-step synthesis in batches of up to 15 g. Al(OTeF₅)₃ and the adduct were characterized by vibrational spectroscopy (IR, Raman) and quantum-chemical calculations. Furthermore, five different salts of the new weakly coordinating anion [Al(OTeF₅)₄]⁻ were prepared in a two-step procedure. [Ph₄P][Al(OTeF₅)₄], Cs[Al(OTeF₅)₄], [Ph₃C][Al(OTeF₅)₄], as well as the protonated benzene derivatives [C₉H₁₃][Al(OTeF₅)₄] and [C₆H₇][Al(OTeF₅)₄] were characterized by low-temperature single-crystal X-ray diffraction and NMR spectroscopy. Arenium salts have rarely been characterized in the solid state and were synthesized in this work in a simplified fashion.     

Bed Bug Aggregation Pheromone Finally Identified

Bed bugs have become a global epidemic and current detection tools are poorly suited for routine surveillance. Despite intense research on bed bug aggregation behavior and the aggregation pheromone, which could be used as a chemical lure, the complete composition of this pheromone has thus far proven elusive. Here, we report that the bed bug aggregation pheromone comprises five volatile components (dimethyl disulfide, dimethyl trisulfide, (E)‐2‐hexenal, (E)‐2‐octenal, 2‐hexanone), which attract bed bugs to safe shelters, and one less‐volatile component (histamine), which causes their arrestment upon contact. In infested premises, a blend of all six components is highly effective at luring bed bugs into traps. The trapping of juvenile and adult bed bugs, with or without recent blood meals, provides strong evidence that this unique pheromone bait could become an effective and inexpensive tool for bed bug detection and potentially their control.     

Nanostructured SnO2-ZnO heterojunction photocatalysts showing enhanced photocatalytic activity for the degradation of organic dyes

Nanoporous SnO(2)-ZnO heterojunction nanocatalyst was prepared by a straightforward two-step procedure involving, first, the synthesis of nanosized SnO(2) particles by homogeneous precipitation combined with a hydrothermal treatment and, second, the reaction of the as-prepared SnO(2) particles with zinc acetate followed by calcination at 500 °C. The resulting nanocatalysts were characterized by X-ray diffraction (XRD), FTIR, Raman, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption analyses, transmission electron microscopy (TEM), and UV-vis diffuse reflectance spectroscopy. The SnO(2)-ZnO photocatalyst was made of a mesoporous network of aggregated wurtzite ZnO and cassiterite SnO(2) nanocrystallites, the size of which was estimated to be 27 and 4.5 nm, respectively, after calcination. According to UV-visible diffuse reflectance spectroscopy, the evident energy band gap value of the SnO(2)-ZnO photocatalyst was estimated to be 3.23 eV to be compared with those of pure SnO(2), that is, 3.7 eV, and ZnO, that is, 3.2 eV, analogues. The energy band diagram of the SnO(2)-ZnO heterostructure was directly determined by combining XPS and the energy band gap values. The valence band and conduction band offsets were calculated to be 0.70 ± 0.05 eV and 0.20 ± 0.05 eV, respectively, which revealed a type-II band alignment. Moreover, the heterostructure SnO(2)-ZnO photocatalyst showed much higher photocatalytic activities for the degradation of methylene blue than those of individual SnO(2) and ZnO nanomaterials. This behavior was rationalized in terms of better charge separation and the suppression of charge recombination in the SnO(2)-ZnO photocatalyst because of the energy difference between the conduction band edges of SnO(2) and ZnO as evidenced by the band alignment determination. Finally, this mesoporous SnO(2)-ZnO heterojunction nanocatalyst was stable and could be easily recycled several times opening new avenues for potential industrial applications.     

From Bad Electrochemical Practices to an Environmental and Waste Reducing Approach for the Generation of Active Hydrogen Evolving Electrodes

The electrodeposition of noble metals using corresponding dissolved metal salts represents an interesting process for the improvement of the electrocatalytic hydrogen evolution reaction (HER) properties of less active substrate materials. The fact that only a small fraction of the dissolved noble metals reaches the substrate represents a serious obstacle to this common procedure. We therefore chose a different path. It was found that the HER activity of Ni42 alloy drastically increased (η=140 mV at j=10 mA cm^?2; pH 1) when a platinum counter electrode was used during polarization experiments in acid. This improvement was caused by a platinum transfer from the platinum anode to the steel cathode, a process which occurred simultaneously to the hydrogen evolution. The negligible accumulation of Pt (26 μg) in the electrolyte turns this straight‐forward transfer procedure into a highly cost‐effective, environmentally friendly, and waste reducing approach for the generation of cheap, stable and effective HER electrodes.     

Synthetic signal injection using inductive coupling

The limited bandwidths of volume selective RF pulses in localized in vivo MRS experiments introduce spatial artifacts that complicate spectral quantification of J-coupled metabolites. These effects are commonly referred to as a spatial interference or "four compartment" artifacts and are more pronounced at higher field strengths. The main focus of this study is to develop a generalized approach to numerical simulations that combines full density matrix calculations with 3D localization to investigate the spatial artifacts and to provide accurate prior knowledge for spectral fitting. Full density matrix calculations with 3D localization using experimental pulses were carried out for PRESS (TE=20, 70 ms), STEAM (TE=20, 70 ms) and LASER (TE=70 ms) pulse sequences and compared to non-localized simulations and to phantom solution data at 4 T. Additional simulations at 1.5 and 7 T were carried out for STEAM and PRESS (TE=20 ms). Four brain metabolites that represented a range from weak to strong J-coupling networks were included in the simulations (lactate, N-acetylaspartate, glutamate and myo-inositol). For longer TE, full 3D localization was necessary to achieve agreement between the simulations and phantom solution spectra for the majority of cases in all pulse sequence simulations. For short echo time (TE=20 ms), ideal pulses without localizing gradients gave results that were in agreement with phantom results at 4 T for STEAM, but not for PRESS (TE=20). Numerical simulations that incorporate volume localization using experimental RF pulses are shown to be a powerful tool for generation of accurate metabolic basis sets for spectral fitting and for optimization of experimental parameters.     

Magneto-optical trapping of radioactive atoms for test of the fundamental symmetries

We are planning test experiments of fundamental symmetries based on the intrinsic properties of francium. It is expected that the laser cooling and trapping of francium will produce precision measurements. The pilot experiment using rubidium was performed with the goal of francium trapping. The ion beam generated with a francium ion source was investigated using a Wien filter. Each piece of equipment still must be studied in more detail, and the equipment should be upgraded in order to trap radioactive atoms.