Molybdenum sputtering film characterization for high gradient accelerating structures

Technological advancements are strongly required to fulfill the demands of new accelerator devices with the highest accelerating gradients and operation reliability for the future colliders. To this purpose an extensive R&D regarding molybdenum coatings on copper is in progress. In this contribution we describe chemical composition, deposition quality and resistivity properties of different molybdenum coatings obtained via sputtering. The deposited films are thick metallic disorder layers with different resistivity values above and below the molibdenum dioxide reference value. Chemical and electrical properties of these sputtered coatings have been characterized by Rutherford backscattering, XANES and photoemission spectroscopy. We will also present a three cells standing wave section coated by a molybdenum layer $\sim$ 500 nm thick designed to improve the performance of X-Band accelerating systems.Comment: manuscript has been submitted and accepted by Chinese Physics C (2012

Télescope comprenant un miroir principal sphérique, à grand champ de vision et à haute résolution optique

Télescope à grand champ de vision, haute résolution optique et continuité du champ de vision comprenant un miroir primaire sphérique, (M1), caractérisé par le fait a) que ledit télescope est équipé d'un système de répartition du champ de vision, b) que ledit système de répartition du champ de vision est placé à proximité du point focal (M1f) du miroir primaire et est constitué d'un miroir (M2) secondaire constitué de surfaces réfléchissantes planes n, (fc1-16) c) que lesdites surfaces réfléchissantes planes n sont contiguës l'une à l'autre et forment un réflecteur continu à facettes prismatiques multiples, de manière à obtenir la continuité du champ de vision sur l'ensemble du champ, d) que lesdites surfaces réfléchissantes planes n sont suivies par un nombre correspondant de correcteurs (C1-n) et de caméras optiques (Rc1 -n) qui forment des portions n d'une image dans des plans focaux n distincts (fp1-n) e) que, sur chaque plan focal n-ième, est positionné un élément collecteur et d'enregistrement

An open access, integrated XAS data repository at Diamond Light Source

The analysis of reference materials is a fundamental part of the data analysis process, in particular for XAS experiments. The beamline users and more generally the XAS community can greatly benefit from the availability of a reliable and wide base of reference sample spectra, acquired in standard and well-characterized experimental conditions. On B18, the Core EXAFS beamline at the Diamond Light Source, in the past years we have collected a series of XAS data on well characterized compounds. This work constitutes the base for a reference sample database, available as a data analysis tool to the general XAS community. This data repository aims to complement the bare spectroscopic information with characterisation, preparation, provenance, analysis and bibliographic references, so improving the traceability of the deposited information. This integrated approach is the base of success and wide distribution of data repositories in other fields, and we hope it will provide on one side a precious facility for the training of students and researchers new to the technique, and at the same time encourage the discussion of best practices in the data analysis process. The database will be open to the contribution of experimental data from the user community, and will provide bibliographic reference information and access control

Displacive order–disorder behavior and intrinsic clustering of lattice distortions in bi‐substituted NaNbO3

Perovskite‐like NaNbO3‐Bi1/3NbO3 solid solutions are studied to understand the interactions between octahedral rotations, which dominate the structural behavior of NaNbO3 and displacive disorder of Bi present in Bi1/3NbO3. Models of instantaneous structures for representative compositions are obtained by refining atomic coordinates against X‐ray total scattering and extended X‐ray‐absorption fine structure data, with additional input obtained from transmission electron microscopy. A mixture of distinct cations and vacancies on the cuboctahedral A‐sites in Na1−3x Bix NbO3 (x ≤ 0.2) results in 3D nanoscale modulations of structural distortions. This phenomenon is determined by the inevitable correlations in the chemical composition of adjacent unit cells according to the structure type—an intrinsic property of any nonmolecular crystals. Octahedral rotations become suppressed as x increases. Out‐of‐phase rotations vanish for x > 0.1, whereas in‐phase tilts persist up to x = 0.2, although for this composition their correlation length becomes limited to the nanoscale. The loss of out‐of‐phase tilting is accompanied by qualitative changes in the probability density distributions for Bi and Nb, with both species becoming disordered over loci offset from the centers of their respective oxygen cages. Symmetry arguments are used to attribute this effect to different strengths of the coupling between the cation displacements and out‐of‐phase versus in‐phase rotations. The displacive disorder of Bi and Nb combined with nanoscale clustering of lattice distortions are primarily responsible for the anomalous broadening of the temperature dependence of the dielectric constant

A crossover from Kondo semiconductor to metallic antiferromagnet with 5d5d-electron doping in CeFe2_2Al10_{10}

We report a systematic study of the $5d$-electron-doped system Ce(Fe$_{1-x}$Ir$_x$)$_2$Al$_{10}$ ($0 \leq x \leq 0.15$). With increasing $x$, the orthorhombic $b$~axis decreases slightly while accompanying changes in $a$ and $c$ leave the unit cell volume almost unchanged. Inelastic neutron scattering, along with thermal and transport measurements, reveal that for the Kondo semiconductor CeFe$_2$Al$_{10}$, the low-temperature energy gap which is proposed to be a consequence of strong c \mhyphen f hybridization, is suppressed by a small amount of Ir substitution for Fe, and that the system adopts a metallic ground state with an increase in the density of states at the Fermi level. The charge or transport gap collapses (at $x=$~0.04) faster than the spin gap with Ir substitution. Magnetic susceptibility, heat capacity, and muon spin relaxation measurements demonstrate that the system undergoes long-range antiferromagnetic order below a N\'eel temperature, $T_{\mathrm{N}}$, of 3.1(2)~K for $x = 0.15$. The ordered moment is estimated to be smaller than 0.07(1)~$\mu_\mathrm{B}$/Ce although the trivalent state of Ce is confirmed by Ce L$_3$-edge x-ray absorption near edge spectroscopy. It is suggested that the c \mhyphen f hybridization gap, which plays an important role in the unusually high ordering temperatures observed in Ce$T_2$Al$_{10}$ ($T$ = Ru and Os), may not be necessary for the onset of magnetic order with a low $T_{\mathrm{N}}$ seen here in Ce(Fe$_{1-x}$Ir$_x$)$_2$Al$_{10}$.Comment: 12 pages, 11 figure

Anethole Supplementation During Oocyte Maturation Improves In Vitro Production of Bovine Embryos

[EN] Oxidative stress is one of the most detrimental factors that affect oocyte developmental competence and embryo development in vitro. The impact of anethole supplementation to in vitro maturation (IVM) media on oocyte maturation and further bovine in vitro embryo production was investigated. Oocytes of slaughterhouse-derived bovine ovaries were placed in IVM with anethole at different concentrations of 30 (AN30), 300 (AN300), and 2000 mg/mL (AN2000), or without (control treatment). The oocytes were assessed for maturation rates, and for reactive oxygen species (ROS) and ferric reducing antioxidant power (FRAP) levels, and mitochondrial membrane potential. Embryo development was assessed by cleavage and blastocyst rates, and embryo cell number. The percentage of metaphase II oocytes were similar among the treatments (range, 77%-96%). Anethole at 300 mg/mL was the only treatment that yielded higher cleavage and embryo development (morula and blastocyst) rates compared to the control treatment. The ROS production in the oocytes after maturation did not differ among treatments. However, oocytes treated with anethole at 300 mg/mL had higher (P < .05) FRAP and mitochondrial membrane potential compared to the control treatment. Furthermore, AN300 treatment increased (P < .05) the average number of total cells in blastocysts compared to the control and AN30 treatments. The use of anethole at 300 mg/mL during IVM is suggested to improve the quantity and quality of bovine embryos produced in vitro. The beneficial effects of anethole on embryonic developmental competence in vitro seems to be related to its capacity to regulate the redox balance and improve mitochondrial function in oocytes and embryos.SINational Council for Scientific and Technolo- gical DevelopmentCoordination for the Improvement of Higher Education Personne

Gapless dynamic magnetic ground state in the charge-gapped trimer iridate Ba4_4NbIr3_3O12_{12}

We present an experimental investigation of the magnetic ground state in Ba$_4$NbIr$_3$O$_{12}$, a fractional valent trimer iridate. X-ray absorption and photoemission spectroscopy show that the Ir valence lies between 3+ and 4+ while Nb is pentavalent. Combined dc/ac magnetization, specific heat, and muon spin rotation/relaxation ($\mu$SR) measurements reveal no magnetic phase transition down to 0.05~K. Despite a significant Weiss temperature ($\Theta_{\mathrm{W}} \sim -15$ to $-25$~K) indicating antiferromagnetic correlations, a quantum spin-liquid (QSL) phase emerges and persists down to 0.1~K. This state likely arises from geometric frustration in the edge-sharing equilateral triangle Ir network. Our $\mu$SR analysis reveals a two-component depolarization, arising from the coexistence of rapidly (90\%) and slowly (10\%) fluctuating Ir moments. Powder x-ray diffraction and Ir-L$_3$edge x-ray absorption fine structure spectroscopy identify ~8-10\% Nb/Ir site-exchange, reducing frustration within part of the Ir network, and likely leading to the faster muon spin relaxation, while the structurally ordered Ir ions remain highly geometrically frustrated, giving rise to the rapidly spin-fluctuating QSL ground state. At low temperatures, the magnetic specific heat varies as $\gamma T + \alpha T^2$, indicating gapless spinon excitations, and possible Dirac QSL features with linear spinon dispersion, respectively.Comment: 27 pages, 15 figure

Identification and manipulation of dynamic active site deficiency-induced competing reactions in electrocatalytic oxidation processes

Electrocatalytic organic compound oxidation reactions (OCORs) have been intensively studied for energy and environmentally benign applications. However, relatively little effort has been devoted to developing a fundamental understanding of OCORs, including the detailed competition with side reactions and activity limitations, thus inhibiting the rational design of high-performance electrocatalysts. Herein, by taking the NiWO4-catalysed urea oxidation reaction (UOR) in aqueous media as an example, the competition between the OCOR and the oxygen evolution reaction (OER) within a wide potential range is examined. It is shown that the root of the competition can be ascribed to insufficient surface concentration of dynamic Ni3+, an active site shared by both the UOR and OER. A similar phenomenon is observed in other OCOR electrocatalysts and systems. To address the issue, a “controllable reconstruction of pseudo-crystalline bimetal oxides” design strategy is proposed to maximise the dynamic Ni3+ population and manipulate the competition between the UOR and the OER. The optimised electrocatalyst delivers best-in-class performance and an ∼10-fold increase in current density at 1.6 V versus the reversible hydrogen electrode for alkaline urea electrolysis compared to those of the pristine materials