Non-Fermi liquid behavior below the Néel temperature in the frustrated heavy fermion magnet UAu2.

The term Fermi liquid is almost synonymous with the metallic state. The association is known to break down at quantum critical points (QCPs), but these require precise values of tuning parameters, such as pressure and applied magnetic field, to exactly suppress a continuous phase transition temperature to the absolute zero. Three-dimensional non-Fermi liquid states, apart from superconductivity, that are unshackled from a QCP are much rarer and are not currently well understood. Here, we report that the triangular lattice system uranium diauride (UAu2) forms such a state with a non-Fermi liquid low-temperature heat capacity [Formula: see text] and electrical resistivity [Formula: see text] far below its Néel temperature. The magnetic order itself has a novel structure and is accompanied by weak charge modulation that is not simply due to magnetostriction. The charge modulation continues to grow in amplitude with decreasing temperature, suggesting that charge degrees of freedom play an important role in the non-Fermi liquid behavior. In contrast with QCPs, the heat capacity and resistivity we find are unusually resilient in magnetic field. Our results suggest that a combination of magnetic frustration and Kondo physics may result in the emergence of this novel state.

Field-Induced Modulated State in the Ferromagnet PrPtAl.

The theory of quantum order-by-disorder (QOBD) explains the formation of modulated magnetic states at the boundary between ferromagnetism and paramagnetism in zero field. PrPtAl has been argued to provide an archetype for this. Here, we report the phase diagram in magnetic field, applied along both the easy a axis and hard b axis. For field aligned to the b axis, we find that the magnetic transition temperatures are suppressed and at low temperature there is a single modulated fan state, separating an easy a axis ferromagnetic state from a field polarized state. This fan state is well explained with the QOBD theory in the presence of anisotropy and field. Experimental evidence supporting the QOBD explanation is provided by the large increase in the T^{2} coefficient of the resistivity and direct detection of enhanced magnetic fluctuations with inelastic neutron scattering, across the field range spanned by the fan state. This shows that the QOBD mechanism can explain field induced modulated states that persist to very low temperature.

Synchrotron X-ray diffraction investigation of the surface condition of artefacts from King Henry VIII's warship the Mary Rose.

Synchrotron X-ray diffraction (XRD) measured on the XMaS beamline at the ESRF was used to characterize the alloy composition and crystalline surface corrosion of three copper alloy Tudor artefacts recovered from the undersea wreck of King Henry VIII's warship the Mary Rose. The XRD method adopted has a dynamic range ∼1:105 and allows reflections <0.002% of the height of major reflections in the pattern to be discerned above the background without smoothing. Laboratory XRD, scanning electron microscopy-energy dispersive spectroscopy, synchrotron X-ray fluorescence and X-ray excited optical luminescence-X-ray near-edge absorption structure were used as supporting techniques, and the combination revealed structural and compositional features of importance to both archaeology and conservation. The artefacts were brass links believed to be fragments of chainmail and were excavated from the seabed during 1981 and 1982. Their condition reflects very different treatment just after recovery, viz. complete cleaning and conservation, chemical corrosion inhibition and chloride removal only, and distilled water soaking only (to remove the chlorides). The brass composition has been determined for all three at least in the top 7 µm or so as Cu(73%)Zn(27%) from the lattice constant. Measurement of the peak widths showed significant differences in the crystallite size and microstrain between the three samples. All of the links are found to be almost chloride-free with the main corrosion products being spertiniite, sphalerite, zincite, covellite and chalcocite. The balance of corrosion products between the links reflects the conservation treatment applied to one and points to different corrosion environments for the other two.

XMaS @ the ESRF.

This paper describes the motivation for the design and construction of a beamline at the European Synchrotron Radiation Facility (ESRF) for the use of UK material scientists. Although originally focused on the study of magnetic materials, the beamline has been running for 20 years and currently supports a very broad range of science as evidenced by the research topics highlighted in this article. We describe how the beamline will adapt to align with the ESRF's upgrade to a diffraction limited storage ring. This article is part of the theme issue 'Fifty years of synchrotron science: achievements and opportunities'.

Photon Energy Becomes the Third Dimension in Crystallographic Texture Analysis.

Conventional analysis of the preferred orientation of crystallites (crystallographic texture) involves X-ray diffraction with area detectors and 2D data output. True 3D, spatially resolved information requires sample rotation in the beam, thus changing the probed volume, which introduces signal smearing and precludes the scanning of complex structures. This obstacle has been overcome by energy-dispersive Laue diffraction. A method has been devised to reach a large portion of reciprocal space and translate the X-ray photon energy into the missing third dimension of space. Carbon fibers and lobster exoskeleton as examples of biomineralized tissue have been analyzed. The major potential of this method lies in its "one-shot" nature and the direct 3D information requiring no previous knowledge of the sample. It allows the texture of large samples with complex substructures to be scanned and opens up the conceptual possibility of following texture changes in situ, for example, during crystallization.

X-ray spectroscopy for chemistry in the 2-4 keV energy regime at the XMaS beamline: ionic liquids, Rh and Pd catalysts in gas and liquid environments, and Cl contamination in γ-Al2O3.

The 2-4 keV energy range provides a rich window into many facets of materials science and chemistry. Within this window, P, S, Cl, K and Ca K-edges may be found along with the L-edges of industrially important elements from Y through to Sn. Yet, compared with those that cater for energies above ca. 4-5 keV, there are relatively few resources available for X-ray spectroscopy below these energies. In addition, in situ or operando studies become to varying degrees more challenging than at higher X-ray energies due to restrictions imposed by the lower energies of the X-rays upon the design and construction of appropriate sample environments. The XMaS beamline at the ESRF has recently made efforts to extend its operational energy range to include this softer end of the X-ray spectrum. In this report the resulting performance of this resource for X-ray spectroscopy is detailed with specific attention drawn to: understanding electrostatic and charge transfer effects at the S K-edge in ionic liquids; quantification of dilution limits at the Cl K- and Rh L3-edges and structural equilibria in solution; in vacuum deposition and reduction of [Rh(I)(CO)2Cl]2 to γ-Al2O3; contamination of γ-Al2O3 by Cl and its potential role in determining the chemical character of supported Rh catalysts; and the development of chlorinated Pd catalysts in `green' solvent systems. Sample environments thus far developed are also presented, characterized and their overall performance evaluated.

Water corrosion of spent nuclear fuel: radiolysis driven dissolution at the UO2/water interface.

X-ray diffraction has been used to probe the radiolytic corrosion of uranium dioxide. Single crystal thin films of UO(2) were exposed to an intense X-ray beam at a synchrotron source in the presence of water, in order to simultaneously provide radiation fields required to split the water into highly oxidising radiolytic products, and to probe the crystal structure and composition of the UO(2) layer, and the morphology of the UO(2)/water interface. By modeling the electron density, surface roughness and layer thickness, we have been able to reproduce the observed reflectivity and diffraction profiles and detect changes in oxide composition and rate of dissolution at the Ångström level, over a timescale of several minutes. A finite element calculation of the highly oxidising hydrogen peroxide product suggests that a more complex surface interaction than simple reaction with H(2)O(2) is responsible for an enhancement in the corrosion rate directly at the interface of water and UO(2), and this may impact on models of long-term storage of spent nuclear fuel.

Incorporation of palladium into pyrite: Insights from X-ray absorption spectroscopy analysis and modelling.

Pyrite (FeS2) often accommodates elevated concentrations of platinum-group elements in ores of magmatic and hydrothermal origin. In order to elucidate the role of pyrite in concentrating Pd, Pd-doped synthetic crystals were studied via X-ray absorption spectroscopy (XAS). Crystals were obtained by salt-flux method in the system saturated with respect to Pd at the temperature of 580 °C and sulphur fugacity of log f (S2) = -0.4. Scanning electron microscopy, electron probe microanalysis, and laser ablation inductively coupled plasma mass spectrometry studies demonstrated a uniform distribution of Pd within the pyrite crystals. The median and average values of Pd content of ∼0.7 ± 0.1 wt% were measured. Comparison of the Pd K-edge X-ray absorption near edge structure (XANES) spectra with the spectra of standards revealed that the formal oxidation state of Pd was close to +2. Fitting of the extended X-ray absorption fine structure (EXAFS) and Finite Difference Method for Near-Edge Structure (FDMNES) theoretical simulations of XANES spectra showed that Pd substituted for Fe in the crystal structure of pyrite. The isomorphous Pd in pyrite was octahedrally coordinated by S atoms at ∼2.385 Å. The PdS interatomic distance was 5.6 % larger than that of FeS due to the difference in their covalent radii of ∼5.3 %. The expansion caused by the incorporation of Pd into the pyrite structure disappeared at the distance of R > 3 Å. The information on the state of Pd in pyrite, including the local atomic environment and formal oxidation state, is essential for scientific and industrial purposes, e.g. physical-chemical modelling and improvement of leaching and extraction processing respectively.

Reversible formation of a PdC(x) phase in Pd nanoparticles upon CO and O2 exposure.

The structure and chemical composition of Pd nanoparticles exposed to pure CO and mixtures of CO and O(2) at elevated temperatures have been studied in situ by a combination of X-ray Diffraction and X-ray Photoelectron Spectroscopy in pressures ranging from ultra high vacuum to 10 mbar and from room temperature to a few hundred degrees celsius. Our investigation shows that under CO exposure, above a certain temperature, carbon dissolves into the Pd particles forming a carbide phase. Upon exposure to CO and O(2) mixtures, the carbide phase forms and disappears reversibly, switching at the stoichiometric ratio for CO oxidation. This finding opens new scenarios for the understanding of catalytic oxidation of C-based molecules.

Formation of wurtzite InP nanowires explained by liquid-ordering.

We report an in situ surface X-ray diffraction study of liquid AuIn metal alloys in contact with zinc-blende InP (111)(B) substrates at elevated temperatures. We observe strong layering of the liquid metal alloy in the first three atomic layers in contact with the substrate. The first atomic layer of the alloy has a higher indium concentration than in bulk. In addition, in this first layer we find evidence for in-plane ordering at hollow sites, which could sterically hinder nucleation of zinc-blende InP. This can explain the typical formation of the wurtzite crystal structure in InP nanowires grown from AuIn metal particles.

Stress-Assisted Thermal Diffusion Barrier Breakdown in Ion Beam Deposited Cu/W Nano-Multilayers on Si Substrate Observed by in Situ GISAXS and Transmission EDX.

The thermal stability of Cu/W nano-multilayers deposited on a Si substrate using ion beam deposition was analyzed in situ by GISAXS and transmission EDX-a combination of methods permitting the observation of diffusion processes within buried layers. Further supporting techniques such as XRR, TEM, WAXS, and AFM were employed to develop an extensive microstructural understanding of the multilayer before and during heating. It was found that the pronounced in-plane compressive residual stress and defect population induced by ion beam deposition result in low thermal stability driven by thermally activated self-interstitial and vacancy diffusion, ultimately leading to complete degradation of the layered structure at moderate temperatures. The formation of Cu protrusions was observed, and a model was formulated for stress-assisted Cu diffusion driven by Coble creep along W grain boundaries, along with the interaction with Si substrate, which showed excellent agreement with the observed experimental data. The model provided the explanation for the experimentally observed strong correlation between thin film deposition conditions, microstructural properties, and low thermal stability that can be applied to other multilayer systems.

Multiscale characterisation of single synthetic fibres: Surface morphology and nanomechanical properties.

HYPOTHESIS: Thermal through-air bonding process and slip additive treatment affect fibre surface structure and nanomechanical properties, which is extremely difficult to characterise on a single-fibre level. EXPERIMENTS: Optical microscopy (OM) was applied to study the effect of air-through bonding, spunbonding, and crimping on fibre geometry and general appearance. A "spray-on" method developed here using a custom-designed fibre holder allowed a direct measurement of static contact angles of water droplets on single fibres. Scanning electron microscopy (SEM) showed different morphological features on the fibre due to the nonwoven fabric-making process and additive treatment. Synchrotron X-ray diffraction (XRD) was applied to study the effect of erucamide presence on polypropylene (PP) fibre crystal structure. Atomic force microscopy (AFM) imaging provided complementary characterization of fibre topographic features such as average surface roughness, along with adhesion force mapping by quantitative nanomechanical (QNM) AFM imaging. FINDINGS: Our results show the effect of nonwoven making process and surfactant additive treatment on the fibre surface structure and nanomechanical properties. Wettability experiment on the single fibre revealed the hydrophobic nature of all the synthetic fibres. For polyethylene/polyethylene terephthalate (PE/PET) bicomponent single fibres, the polyethylene sheath was found to possess fibrillar microstructure - typical for drawn fibres, whereas the fibres entangled in nonwoven fabrics exhibited a uniform, porous surface morphology attributed to the through-air process. Adhesion force mapping allowed us to correlate fibre nanomechanical properties with its topography, with surface pore interiors showing higher adhesion than the flat polyethylene region. Furthermore, on the polypropylene (PP) fibre surface treated with erucamide (13-cis-docosenamide; a common slip additive used in polyolefin film processing), we observed overlapping multilayers consisting of 4 nm erucamide bilayers, attributed to the slip additive migration onto the fibre surface. XRD measurements of the fibres did not detect the presence of erucamide; however, AFM imaging provided evidence for its migration to the fibre surface, imparting influence on the surface structure and adhesive properties of the fibre. Single-fibre AFM imaging also allowed a detailed analysis of different surface roughness parameters, revealing that both through-air bonding in the nonwoven making process and the slip additive (erucamide) treatment affected the fibre surface roughness. The wettability, surface morphology, and adhesion properties from this study, obtained with unprecedented resolution and details on single fibres, are valuable to informing rational design of fibre processing for fibre optimal properties, critically important in many industrial applications.

SR-XRD in situ monitoring of copper-IUD corrosion in simulated uterine fluid using a portable spectroelectrochemical cell.

The objective of this work is to study the initial corrosion of copper in the presence of gold when placed in simulated uterine fluid in order to better understand the evolution of active components of copper-IUDs. In order to carry out this study, a portable cell was designed to partially simulate the uterine environment and provide a way of tracking the chemical changes occurring in the samples in situ within a controlled environment over a long period of time using synchrotron spectroelectrochemistry. The dynamically forming crystalline corrosion products are determined in situ for a range of copper-gold surface ratios over the course of a 10-day experiment in the cell. It is concluded that the insoluble deposits forming over this time are not the origin of the anticonception mechanism.

The role of steps in surface catalysis and reaction oscillations.

Atomic steps at the surface of a catalyst play an important role in heterogeneous catalysis, for example as special sites with increased catalytic activity. Exposure to reactants can cause entirely new structures to form at the catalyst surface, and these may dramatically influence the reaction by 'poisoning' it or by acting as the catalytically active phase. For example, thin metal oxide films have been identified as highly active structures that form spontaneously on metal surfaces during the catalytic oxidation of carbon monoxide. Here, we present operando X-ray diffraction experiments on a palladium surface during this reaction. They reveal that a high density of steps strongly alters the stability of the thin, catalytically active palladium oxide film. We show that stabilization of the metal, caused by the steps and consequent destabilization of the oxide, is at the heart of the well-known reaction rate oscillations exhibited during CO oxidation at atmospheric pressure.

Mercury binding sites in thiol-functionalized mesostructured silica.

Thiol-functionalized mesostructured silica with anhydrous compositions of (SiO(2))(1)(-)(x)()(LSiO(1.5))(x)(), where L is a mercaptopropyl group and x is the fraction of functionalized framework silicon centers, are effective trapping agents for the removal of mercuric(II) ions from water. In the present work, we investigate the mercury-binding mechanism for representative thiol-functionalized mesostructures by atomic pair distribution function (PDF) analysis of synchrotron X-ray powder diffraction data and by Raman spectroscopy. The mesostructures with wormhole framework structures and compositions corresponding to x = 0.30 and 0.50 were prepared by direct assembly methods in the presence of a structure-directing amine porogen. PDF analyses of five mercury-loaded compositions with Hg/S ratios of 0.50-1.30 provided evidence for the bridging of thiolate sulfur atoms to two metal ion centers and the formation of chain structures on the pore surfaces. We find no evidence for Hg-O bonds and can rule out oxygen coordination of the mercury at greater than the 10% level. The relative intensities of the PDF peaks corresponding to Hg-S and Hg-Hg atomic pairs indicate that the mercury centers cluster on the functionalized surfaces by virtue of thiolate bridging, regardless of the overall mercury loading. However, the Raman results indicate that the complexation of mercury centers by thiolate depends on the mercury loading. At low mercury loadings (Hg/S < or = 0.5), the dominant species is an electrically neutral complex in which mercury most likely is tetrahedrally coordinated to bridging thiolate ligands, as in Hg(SBu(t))(2). At higher loadings (Hg/S 1.0-1.3), mercury complex cations predominate, as evidenced by the presence of charge-balancing anions (nitrate) on the surface. This cationic form of bound mercury is assigned a linear coordination to two bridging thiolate ligands.

Observation of novel liquid-crystalline phase above the bulk-melting temperature.

In this paper, we show that a noncrystalline but ordered smectic-like phase exists above the bulk-melting temperature (T(m)) at poly(n-alkyl acrylates)-air interface. The surface ordered phase is one monolayer thick and undergoes a sharp transition from order to disorder 10 degrees C above T(m) for n=22. The presence of a surface phase that does not exist in the bulk has important implications in the design of thermally responsive adhesives.