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80 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS I11-High Resolution Powder Diffraction	Fe K-edge X-ray Absorption Spectroscopy of corrosion phases of archaeological iron: results, limitations, and the need for complementary techniques Hayley Simon , Giannantonio Cibin , Ian Freestone , Eleanor Schofield Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/ac08b6 Diamond Proposal Number(s): [16328] Open Access Show Abstract ▼ Abstract: Data analysis methods for iron X-ray Absorption Spectroscopy (XAS) can provide extensive information about the oxidation state and co-ordination of an Fe-species. However, the extent to which techniques developed using a single-phase iron sample may be applied to complex, mixed-phase samples formed under real-world conditions is not clear. This work uses a combination of pre-edge fitting and linear combination analysis (LCA) to characterise the near edge region of the X-ray absorption spectrum (XANES) for a set of archaeological iron corrosion samples from a collection of cast iron cannon shot excavated from the Mary Rose shipwreck and compares the data with phase compositions determined by Synchrotron X-ray Powder Diffraction (SXPD). Archaeological powder and cross-section samples were compared to a library of iron standards and diffraction data. The XANES are consistent with previous observations that generation of the chlorinated phase akaganeite, β-FeO(OH,Cl), occurs in those samples which have been removed form passive storage and subjected to active conservation. However, the results show that if any metallic species is present in the sample, the contribution from Fe(0) to the spectral region containing a pre-edge for oxidised iron – Fe(II) and Fe(III) – causes the analysis to be less effective and the conclusions unreliable. Consequently, while the pre-edge fitting methodology may be applied to a mixture of iron oxides or oxyhydroxides, the procedure is inappropriate for a mixed metal-oxide sample without the application of a complimentary technique, such as SXPD.	Jun 2021
I20-Scanning-X-ray spectroscopy (XAS/XES)	Photon-in/photon-out spectroscopy at the I20-scanning beamline at Diamond Light Source Shusaku Hayama , Roberto Boada , Jesus Chaboy , Adrian Birt , Graham Duller , Leo Cahill , Adam Freeman , Monica Amboage , Luke Keenan , Sofia Diaz-Moreno Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/abfe93 Open Access Show Abstract ▼ Abstract: A scanning multi-crystal x-ray emission spectrometer to perform photon-in/photon-out spectroscopy at the I20-Scanning beamline at Diamond Light Source is described. The instrument, equipped with three analyzer crystals, is based on a 1m Rowland circle spectrometer operating in the vertical plane. The energy resolution of the spectrometer is of the order of 1 eV, having sufficient resolving power to overcome the core-hole lifetime broadening of most of the transition metals K-edges. Examples showing the capabilily of the beamline for performing high energy resolution fluorescence detection x-ray absorption spectroscopy (HERFD-XAS), non-resonant x-ray emission spectroscopy (XES) and resonant x-ray emission spectroscopy (RXES) are presented. The comparison of the Zn and Mn K-edge HERFD-XANES of ZnO and MnO with ab-initio calculations shows that the technique provides enhanced validation of the models by making subtle spectral features more visible.	May 2021
B18-Core EXAFS	Operando XAFS investigation on the effect of ash deposition on three-way catalyst used in Gasoline Particulate Filters and the effect of the manufacturing process on the catalytic activity Monik Panchal , June Callison , Vainius Skukauskas , Diego Gianolio , Giannantonio Cibin , Andrew P. E. York , Manfred Erwin Schuster , Timothy I. Hyde , Paul Collier , C. Richard A. Catlow , Emma K. Gibson Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/abfe16 Diamond Proposal Number(s): [24156] Open Access Show Abstract ▼ Abstract: Platinum group metals (PGM) such as palladium and rhodium based catalysts are currently being implemented in Gasoline Particulate Filter (GPF) autoexhaust aftertreatment systems. However, little is known about how the trapped particulate matter, such as the incombustible ash, interacts with the catalyst and so may affect its performance. This operando study follows the evolution of the Pd found in two different model GPF systems: one containing ash components extracted from a GPF and another from a catalyst washcoat prior to adhesion onto the GPF. We show that the catalytic activity of the two systems vary when compared with a 0 g ash containing GPF. Compared to the 0 g ash sample the 20 g ash containing sample had a higher CO light off temperature, in addition, an oscillation profile for CO, CO2 and O2 was observed, which is speculated to be a combination of CO oxidation, C deposition via a Boudouard Reaction and further partial oxidation of the deposited species to CO. During the ageing procedure the washcoat sample reduces NO at a lower temperature than the 0 g ash sample. However, post ageing the 0 g ash sample recovers and both samples reduce NO at 310 circleC. In comparison, the 20 g ash GPF sample maintains a higher NO reduction temperature of 410 circleC post ageing, implying that the combination of high temperature ageing and presence of ash has an irreversible negative effect on catalyst performance.	May 2021
I20-EDE-Energy Dispersive EXAFS (EDE)	A novel fuel cell design for operando energy-dispersive X-ray absorption measurements Andrew S. Leach , Jennifer Hack , Monica Amboage , Sofia Diaz-Moreno , Haoliang Huang , Patrick L. Cullen , Martin Wilding , Emanuele Magliocca , Thomas Miller , Christopher Howard , Daniel Brett , Paul Shearing , Paul F. Mcmillan , Andrea E. Russell , Rhodri Jervis Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/ac0476 Diamond Proposal Number(s): [22008, 15650] Open Access Show Abstract ▼ Abstract: A polymer electrolyte fuel cell (PEFC) has been designed to allow operando X-ray absorption spectroscopy (XAS) measurements of catalysts. The cell has been developed to operate under standard fuel cell conditions, with elevated temperatures and humidification of the gas-phase reactants, both of which greatly impact the catalyst utilisation. X-ray windows in the endplates of the cell facilitate collection of XAS spectra during fuel cell operation while maintaining good compression in the area of measurement. Results of polarisation curves and cyclic voltammograms (CVs) showed that the operando cell performs well as a fuel cell, while also providing XAS data of suitable quality for robust XANES analysis. The cell has produced comparable XAS results when performing a cyclic voltammogram to an established in situ cell when measuring the Pt LIII edge. Similar trends of Pt oxidation, and reduction of the formed Pt oxide, have been presented with a time resolution of 5 seconds for each spectrum, paving the way for time-resolved spectral measurements of fuel cell catalysts in a fully-operating fuel cell.	May 2021
B18-Core EXAFS	Monitoring the process of formation of ZnO from ZnO2 using in situ combined XRD/XAS technique Thomas Daley , Kwasi Opuni , Edwin Raj , Andrew J. Dent , Giannantonio Cibin , Timothy I Hyde , Gopinathan Sankar Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/abfb91 Diamond Proposal Number(s): [6966] Open Access Show Abstract ▼ Abstract: Use of in situ combined X-ray diffraction and X-ray absorption spectroscopy for the study of the thermal decomposition of zinc peroxide to zinc oxide is reported here. Comparison of data extracted from both X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) with thermo gravimetric analysis (TGA) enabled us to follow the nature of the conversion of ZnO2 to ZnO. A temperature range between 230 and 350oC appears to show a very poorly crystalline ZnO is formed prior to the formation of ordered ZnO material. Both the decrease in white line intensity in the Zn K-edge XANES and resulting lower coordination numbers estimated from analysis of Zn K-edge data of ZnO heated at 500oC, in comparison to bulk ZnO, suggest that that the ZnO produced by this method has significant defects in the system.	Apr 2021
	Determination of the preferred reaction pathway of acetophenone on Si(001) using photoelectron diffraction Paula Laborda Lalaguna , Holly Hedgeland , Paul Ryan , Oliver Warschkow , Matthias Muntwiler , Andrew Teplyakov , Steven R Schofield , David Andrew Duncan Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/abe6dd Open Access Show Abstract ▼ Abstract: The adsorption configurations of a technologically relevant model organic adsorbate on the silicon (001) surface were studied using energy scanned X-ray photoelectron diffraction (PhD). Previous work has established the existence of an interesting vertically-aligned ("flagpole") configuration, where the acetophenone attaches to Si(001) via the acetyl group carbon and oxygen atoms. DFT calculations have predicted two energetically similar variants of this structure, where the phenyl ring is orientated parallel or perpendicular to the rows of silicon dimers on this reconstructed surface. However, previously published experimental measurements, including scanning tunnelling microscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure investigations were unable to distinguish between these two configurations. Here, we apply the unique experimental capabilities of the PhD technique to this system and demonstrate that the dominant adsorption configuration has the phenyl ring parallel to the dimer rows (the end-bridge structure). This information in turn facilitates the determination of the dominant reaction pathway for acetophenone on Si(001), which has remained elusive until now. Information about subtle preferences in reaction pathways that affect the alignment and orientation of organic adsorbates such as acetophenone on technologically-relevant semiconductor surfaces such as Si(001) is critical for the fabrication of future atomically-precise atomic and molecular-scale electronic devices utilising the organic-silicon interface, and this work demonstrates the unique and complementary capabilities of PhD for providing this information.	Feb 2021
	The nuts and bolts of core-hole constrained ab initio simulation for K-shell x-ray photoemission and absorption spectra Benedikt P. Klein , Samuel J Hall , Reinhard J Maurer Journal Of Physics: Condensed Matter 33 DOI: 10.1088/1361-648X/abdf00 Open Access Show Abstract ▼ Abstract: X-ray photoemission (XPS) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy play an important role in investigating the structure and electronic structure of materials and surfaces. Ab initio simulations provide crucial support for the interpretation of complex spectra containing overlapping signatures. Approximate core-hole simulation methods based on density functional theory (DFT) such as the delta-self-consistent-field (ΔSCF) method or the transition potential (TP) method are widely used to predict K-shell XPS and NEXAFS signatures of organic molecules, inorganic materials and metal–organic interfaces at reliable accuracy and affordable computational cost. We present the numerical and technical details of our variants of the ΔSCF and TP method (coined ΔIP-TP) to simulate XPS and NEXAFS transitions. Using exemplary molecules in gas-phase, in bulk crystals, and at metal–organic interfaces, we systematically assess how practical simulation choices affect the stability and accuracy of simulations. These include the choice of exchange–correlation functional, basis set, the method of core-hole localization, and the use of periodic boundary conditions (PBC). We particularly focus on the choice of aperiodic or periodic description of systems and how spurious charge effects in periodic calculations affect the simulation outcomes. For the benefit of practitioners in the field, we discuss sensible default choices, limitations of the methods, and future prospects.	Feb 2021
I15-Extreme Conditions	The phase diagram of Ti-6Al-4V at high-pressures and high-temperatures Simon Macleod , Daniel Errandonea , Geoffrey Adam Cox , Hyunchae Cynn , Dominik Daisenberger , Sarah Finnegan , Malcolm Mcmahon , Keith Munro , Catalin Popescu , Christian Storm Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/abdffa Diamond Proposal Number(s): [8176, 9366] Open Access Show Abstract ▼ Abstract: We report results from a series of diamond-anvil-cell synchrotron X-ray diffraction and largevolume- press experiments, and calculations, to investigate the phase diagram of commercial polycrystalline high-strength Ti-6Al-4V alloy in pressure-temperature space. Up to ~30 GPa and 886 K, Ti- 6Al-4V is found to be stable in the hexagonal-close-packed, or alpha phase. The effect of temperature on the volume expansion and compressibility of alpha-Ti-6Al-4V is modest. The martensitic alpha→omega (hexagonal) transition occurs at ~30 GPa, with both phases coexisting until further compression to ~38-40 GPa completes the transition to the omega phase. Between 300 K and 844 K the alpha→omega transition appears to be independent of temperature. Omega-Ti-6Al-4V is stable to ~91 GPa and 844 K, the highest combined pressure and temperature reached in these experiments. Pressure-volume-temperature equations-of-state for the alpha and omega phases of Ti- 6Al-4V are generated and found to be similar to pure Ti. A pronounced hysteresis is observed in the omega-Ti-6Al-4V on decompression, with the hexagonal structure reverting back to the  alpha phase at pressures below ~9 GPa at room temperature, and at a higher pressure at elevated temperatures. Based on our data, we estimate the Ti-6Al-4V alpha-beta-omega triple point to occur at ~900 K and 30 GPa, in good agreement with our calculations.	Jan 2021
B16-Test Beamline B18-Core EXAFS I08-Scanning X-ray Microscopy beamline (SXM)	Studying the onset of galvanic steel corrosion in situ using thin films: film preparation, characterization and application to pitting Debi Garai , Vladyslav Solokha , Axel Wilson , Ilaria Carlomagno , Ajay Gupta , Mukul Gupta , V. R. Reddy , Carlo Meneghini , Francesco Carla , Christian Morawe , Jorg Zegenhagen Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/abd523 Diamond Proposal Number(s): [17145] Open Access Show Abstract ▼ Abstract: This work reports about a novel approach for investigating surface processes during the early stages of galvanic corrosion of stainless steel in situ by employing ultra-thin films and synchrotron X-radiation. Characterized by X-ray techniques and voltammetry, such films, sputter deposited from austenitic steel, were found representing useful replicas of the target material. Typical for stainless steel, the surface consists of a passivation layer of Fe- and Cr-oxides, a couple of nm thick, that is depleted of Ni. Films of ≈ 4 nm thickness were studied in situ in an electrochemical cell under potential control (-0.6 to +0.8 V vs Ag/AgCl) during exposure to 0.1 M KCl. Material transport was recorded with better than 1/10 monolayer sensitivity by X-ray spectroscopy. Leaching of Fe was observed in the cathodic range and the therefor necessary reduction of Fe-oxide appears to be accelerated by atomic hydrogen. Except for minor leaching, reduction of Ni, while expected from Pourbaix diagram, was not observed until at ≈ +0.8 V Cr-oxide was removed from the film. After couple of minutes exposure at +0.8 V, the current in the electrochemical cell revealed a rapid pitting event that was simultaneously monitored by X-ray spectroscopy. Continuous loss of Cr and Ni was observed during the induction time leading to the pitting, suggesting a causal connection with the event. Finally, a spectroscopic image of a pit was recorded ex situ with 50 nm lateral and 1 nm depth resolution by soft X-ray scanning absorption microscopy at the Fe L2,3-edges by using a 80 nm film on a SiN membrane, which is further demonstrating the usefulness of thin films for corrosion studies.	Dec 2020
I21-Resonant Inelastic X-ray Scattering (RIXS)	Resonant inelastic x-ray spectroscopy on UO$_{2}$ as a test case for actinide materials G. H. Lander , Martin Sundermann , Ross Springell , Andrew Walters , Abhishek Nag , Mirian Garcia-Fernandez , Ke-Jin Zhou , Gerrit Van Der Laan , Roberto Caciuffo Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/abc4d2 Diamond Proposal Number(s): [24583] Open Access Show Abstract ▼ Abstract: Resonant inelastic x-ray spectroscopy at the uranium $N_{4}$ absorption edge at 778 eV has been used to reveal the excitations in UO$_{2}$ up to 1 eV. The earlier (1989) studies by neutron inelastic scattering of the crystal-field states within the $^{3}H_{4}$ multiplet are confirmed. In addition, the first excited state of the $^{3}F_{2}$ multiplet at $\sim$520 meV has been established, and there is a weak signal corresponding to the next excited state at $\sim$920 meV. This represents a successful application of soft x-ray spectroscopy to an actinide sample, and resolves an open question in UO$_{2}$ that has been discussed for 50 years. The technique is described and important caveats are drawn about possible future applications.	Oct 2020

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