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Scan free grazing emission X ray fluorescence spectroscopy GEXRF is an established technique for the investigation of the elemental depth profiles of various samples. Recently it has been applied to investigating structured nanosamples in the tender X ray range. However, lighter elements such as oxygen, nitrogen or carbon cannot be efficiently investigated in this energy range, because of the ineffective excitation. Moreover, common CCD detectors are not able to discriminate between fluorescence lines below 1 keV. Oxygen and nitrogen are important components of insulation and passivation layers, for example, in silicon oxide or silicon nitride. In this work, scan free GEXRF is applied in proof of concept measurements for the investigation of lateral ordered 2D nanostructures in the soft X ray range. The sample investigated is a Si3N4 lamellar grating, which represents 2D periodic nanostructures as used in the semiconductor industry. The emerging two dimensional fluorescence patterns are recorded with a CMOS detector. To this end, energy dispersive spectra are obtained via single photon event evaluation. In this way, spatial and therefore angular information is obtained, while discrimination between different photon energies is enabled. The results are compared to calculations of the sample model performed by a Maxwell solver based on the finite elements method. A first measurement is carried out at the UE56 2 PGM 2 beamline at the BESSY II synchrotron radiation facility to demonstrate the feasibility of the method in the soft X ray range. Furthermore, a laser produced plasma source LPP is utilized to investigate the feasibility of this technique in the laboratory. The results from the BESSY II measurements are in good agreement with the simulations and prove the applicability of scan free GEXRF in the soft X ray range for quality control and process engineering of 2D nanostructures. The LPP results illustrate the chances and challenges concerning a transfer of the methodology to the laboratory

FeNi Hydroxides (FeNi-HD) have been considered as promising substitutes to noble metal electrocatalysts for oxygen evolution reaction (OER). In this work, we design and realize FeNi-HD nanotube arrays (FeNi-HDNAs) on Ni foam via an in-situ reaction and Kirkendall effect. The obtained catalysts possess higher specific surface area, more catalytic active sites and better chemical stability for OER. Electron migrations from the Fe 3d orbitals to Ni sites in the FeNi-HDNAs lead to more unoccupied Fe 3d states and a higher oxidation state. As expected, FeNi-HDNAs exhibit lower overpotential as well as lower Tafel slope and better durability than the Fe- or Ni-HD peers. DFT calculations elucidate that FeNi hydroxides lower the energy barrier of rate-determining step in OER. Moreover, a high current density of 10 mA cm−2 is obtained at a low potential of 1.49 V using FeNi-HDNAs as the bifunctional electrocatalyst for overall water splitting in basic solution.

We report on the surface sensitive grazing emission X ray fluorescence technique combined with synchrotron radiation excitation and high resolution detection to realize depth profile measurements of Al implanted Si wafers. The principles of grazing emission measurements as well as the benefits offered by synchrotron sources and wavelength dispersive detection setups are presented. It is shown that the depth distribution of implanted ions can be extracted from the dependence of the X ray fluorescence intensity on the grazing emission angle with nanometer scale precision provided that an analytical function describing the shape of the depth distribution is assumed beforehand. If no a priori assumption is made except a bell shaped form for the dopant distribution the profile derived from the measured angular distribution is found to reproduce quite satisfactorily the depth distribution of the implanted ions.

We evaluated the influence of environmental and density-dependent factors (intraspecific and interspecific) on clutch size, brood size, and nesting success of Little Egrets (Egretta garzetta) in the Camargue of southern France. We recorded these reproductive parameters in most years from 1970 to 1998. We used a generalized linear modeling approach (model selection based on AIC) to examine the environmental effects of spring rainfall, winter temperature, and wind on these parameters. We also examined density dependence of these parameters based on the total number of Little Egrets and the total number of tree-nesting herons nesting in these mixed-species colonies. Clutch size was positively associated with rainfall and negatively associated with the number of Little Egret nests in the Camargue. Brood size was negatively associated with the number of Little Egret nests, although rainfall was only significant as an interaction effect with these two effects. Nesting success was negatively associated with the number of tree-nesting herons, the proportion of each colony consisting of Cattle Egrets (Bubulcus ibis), wind speed, and several interactions among these variables. Virtually all of the reproductive parameters that we evaluated were negatively associated with the number of Little Egret nests or the number of tree-nesting herons. Anecdotal evidence suggests that Cattle Egrets displace Little Egrets at some centrally located nest sites. Such sites are better protected from strong winds, which are a common cause of nesting failure.

International audience

International audience

The electron induced L3M two step double ionization cross sections of metallic Pd were determined experimentally for incident electron beam energies ranging from the double ionization threshold up to 18 keV. The double L3M ionization cross sections were derived from the intensity ratios [I(LaM):[I(La)] of the resolved M satellites to the parent diagram lines. The sample was bombarded with monoenergetic electrons from an energy tunable 20 kV electron gun. The diagram and M satellite x ray lines were measured by means of high resolution x ray spectroscopy using a reflection type von Hamos bent crystal spectrometer. The two step partial cross sections were determined by subtracting from the measured total double ionization cross sections the contributions due to the shake process and L1 L3M45 Coster Kronig transitions. Despite the thick target employed in the present study the dependence of the two step cross sections on the incoming electron energy could be derived using a target slice decomposition method. It is shown that the obtained energy dependence can be well reproduced by the semiempirical parametrization model of Pattard and Rost.

Single photon double K shell ionization of low Z neutral atoms in the range 12?Z?23 is investigated. The experimental method was based on measurements of the high resolution Kah hypersatellite x ray spectra following the radiative decay of the K shell double vacancy states excited by monochromatic synchrotron radiation. The photon energy dependence of the double K shell ionization was measured over a wide range of photon energies from threshold up to and beyond the maximum of the double to single photoionization cross section ratios. From the high resolution x ray emission spectra the energies and linewidths of the hypersatellite transitions as well as the Kah1:Kah2 intensity ratios were determined. The relative importance of the initial state and final state electron electron interactions to the K shell double photoionization is addressed. Physical mechanisms and scaling laws of the K shell double photoionization are examined. A semiempirical universal scaling of the double photoionization cross sections with the effective nuclear charge for neutral atoms in the range 2?Z?47 is established.