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14,963 items found (0 items not approved), displaying 41 to 50.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
	Magnetic circular dichroism elucidates molecular interactions in aggregated chiral organic materials Alessio Gabbani , Andrea Taddeucci , Marco Bertuolo , Francesco Pineider , Laura Antonella Aronica , Lorenzo Di Bari , Gennaro Pescitelli , Francesco Zinna Angewandte Chemie International Edition DOI: 10.1002/anie.202313315 Show Abstract ▼ Abstract: Chiral materials formed by aggregated organic compounds play a fundamental role in chiral optoelectronics, photo- and spin-tronics. Nonetheless, a precise understanding of the molecular interactions involved remains an open problem. Here we introduce magnetic circular dichroism (MCD) as a new tool to elucidate molecular interactions and structural parameters of a supramolecular system. A detailed analysis of MCD together with electronic circular dichroism spectra combined to ab initio calculations unveils essential information on the geometry and energy levels of a self-assembled thin film made of a carbazole di-bithiophene chiral molecule. This approach can be extended to a generality of chiral organic materials and can help rationalizing the fundamental interactions leading to supramolecular order. This in turn could enable a better understanding of structure-property relationships, resulting in a more efficient material design.	Nov 2023
I11-High Resolution Powder Diffraction	Forming bonds between molecules and communities through Project M Claire Murray , Laura Holland , Rebecca O'Brien , Julia E. Parker Frontiers In Communication 8 DOI: 10.3389/fcomm.2023.1229616 Diamond Proposal Number(s): [15723] Open Access Show Abstract ▼ Abstract: Calcium carbonate is a compound that is well-recognized and very prevalent in daily life e.g., chalk, mussel shells and limescale. However, scientists still have many questions about its formation mechanisms, the different crystal forms it takes, and how we can control and direct this formation to produce this material with different properties. Project M was a chemistry citizen science project for UK secondary schools exploring the synthesis of samples of calcium carbonate under different reaction conditions and analyzing them at Beamline I11, an X-ray diffraction laboratory at the Diamond Light Source synchrotron. Science communication played a crucial role in the success of the project, connecting different communities to the science and creating unique opportunities to center and empower the Project M Scientists.	Nov 2023
I11-High Resolution Powder Diffraction	Spin-orbital correlations from complex orbital order in MgV2O4 H. Lane , P. M. Sarte , K. Guratinder , A. M. Arevalo-Lopez , R. S. Perry , E. C. Hunter , T. Weber , B. Roessli , A. Stunault , Y. Su , R. A. Ewings , S. D. Wilson , P. Böni , J. P. Attfield , C. Stock Physical Review Research 5 DOI: 10.1103/PhysRevResearch.5.043146 Open Access Show Abstract ▼ Abstract: MgV 2 O 4 is a spinel based on magnetic V 3 + ions, which host both spin ( S = 1 ) and orbital ( l eff = 1 ) moments. Owing to the underlying pyrochlore coordination of the magnetic sites, the spins in MgV 2 O 4 only antiferromagnetically order once the frustrating interactions imposed by the F d ¯ 3 m lattice are broken through an orbitally-driven structural distortion at T S ≃ 60 K. Consequently, a Néel transition occurs at T N ≃ 40 K. Low-temperature spatial ordering of the electronic orbitals is fundamental to both the structural and magnetic properties; however, considerable discussion on whether it can be described by complex or real orbital ordering is ambiguous. We apply neutron spectroscopy to resolve the nature of the orbital ground state and characterize hysteretic spin-orbital correlations using x-ray and neutron diffraction. Neutron spectroscopy finds multiple excitation bands and we parametrize these in terms of a multilevel (or excitonic) theory based on the orbitally degenerate ground state. Meaningful for the orbital ground state, we report an “optical-like” mode at high energies that we attribute to a crystal-field-like excitation from the spin-orbital j eff = 2 ground-state manifold to an excited j eff = 1 energy level. We parametrize the magnetic excitations in terms of a Hamiltonian with spin-orbit coupling and local crystalline electric field distortions resulting from deviations from perfect octahedra surrounding the V 3 + ions. We suggest that this provides compelling evidence for complex orbital order in MgV 2 O 4 . We then apply the consequences of this model to understand hysteretic effects in the magnetic diffuse scattering where we propose that MgV 2 O 4 displays a high-temperature orbital memory of the low-temperature spin order.	Nov 2023
I24-Microfocus Macromolecular Crystallography	Mechanism of substrate binding and transport in BASS transporters Patrick Becker , Fiona Naughton , Deborah Brotherton , Raul Pacheco-Gomez , Oliver Beckstein , Alexander D. Cameron Elife 12 DOI: 10.7554/eLife.89167.3 Diamond Proposal Number(s): [19880] Open Access Show Abstract ▼ Abstract: The bile acid sodium symporter (BASS) family transports a wide array of molecules across membranes, including bile acids in humans, and small metabolites in plants. These transporters, many of which are sodium-coupled, have been shown to use an elevator mechanism of transport, but exactly how substrate binding is coupled to sodium ion binding and transport is not clear. Here, we solve the crystal structure at 2.3 Å of a transporter from Neisseria meningitidis (ASBTNM) in complex with pantoate, a potential substrate of ASBTNM. The BASS family is characterised by two helices that cross-over in the centre of the protein in an arrangement that is intricately held together by two sodium ions. We observe that the pantoate binds, specifically, between the N-termini of two of the opposing helices in this cross-over region. During molecular dynamics simulations the pantoate remains in this position when sodium ions are present but is more mobile in their absence. Comparison of structures in the presence and absence of pantoate demonstrates that pantoate elicits a conformational change in one of the cross-over helices. This modifies the interface between the two domains that move relative to one another to elicit the elevator mechanism. These results have implications, not only for ASBTNM but for the BASS family as a whole and indeed other transporters that work through the elevator mechanism.	Nov 2023
	Scanning photoelectron microscopy discloses the role of Cr and Mo in the selective corrosion of hardmetal grades with Co-Ni binders Benedetto Bozzini , Matteo Amati , Luca Gregoratti , Majid Kazemian Abyaneh , Francesco Tavola , Sandra Tedeschi , Gian Pietro De Gaudenzi International Journal Of Refractory Metals And Hard Materials vol. 184 DOI: 10.1016/j.ijrmhm.2023.106479 Show Abstract ▼ Abstract: Advanced applications of hardmetal (HM) in chemically aggressive ambients call for the improvement of their corrosion resistance, combined with optimal abrasion and toughness properties. This goal is chiefly achieved with binder alloying. In particular, Cr and Mo additions to Co-Ni matrices have proved effective in many cases, but the physico-chemical mechanisms underlying this functional improvement are poorly understood. This situation, on the one hand does not enable the fine-tuning of the composition, and, on the other hand, does not allow to reliably extrapolate the performance of these grades to new ambients. The aim of this work is to propose a molecular-level approach to the understanding of the electrochemical corrosion of HM, based on space-resolved compositional and chemical-state analysis of the surface of HM subjected to controlled electrochemical corrosion. This type of analysis is enabled by synchrotron-based scanning photoelectron microscopy (SPEM) and photoelectron microspectroscopy (μ-XPS). Specifically, we studied a WC-based grade with 15 w% binder with 4.67 Co/Ni ratio, alloyed with 0.78 w% Cr and 0.94 w% Mo, corroded potentiostatically in neutral sulphate aqueous solution in the pseudopassive and transpassive ranges. SPEM and μ-XPS allowed to locate and distinguish the chemical state of the binder and carbide elements in the respective phases and to distinguish the surface stoichiometry brought about by corrosion in different conditions. In particular, we found that pseudopassive conditions lead to the formation of surface films, enriched in W(VI) and Cr(III). Transpassive conditions cause notable surface enrichment in Cr(III) as well as to the formation of mixed Cr-W oxides in the WC regions. Mo is leached from the binder at all potentials investigated, while Mo(0) is present in the WC region under pseudopassive conditions, while transpassivity leads to its oxidative removal. Chloride in the electrolyte favours dissolution of oxidized metals, in particular causing the leaching of Cr(III), while Mo(III) is found at the surface of WC grains.	Nov 2023
I12-JEEP: Joint Engineering, Environmental and Processing	Microstructural stability and evolution in a new polycrystalline Ni-base superalloy G. J. Wise , N. L. Church , C. E. P. Talbot , P. M. Mignanelli , M. C. Hardy , N. G. Jones , H. J. Stone Metallurgical And Materials Transactions A 64 DOI: 10.1007/s11661-023-07211-9 Diamond Proposal Number(s): [30411, 31965] Open Access Show Abstract ▼ Abstract: Polycrystalline Ni-base superalloys that offer equivalent or superior performance to current commercial alloys at lower overall cost are of widespread industrial interest. In this work, a new polycrystalline Ni-base superalloy with low elemental cost has been characterized and compared to current commercially available alternatives. Through a combination of scanning electron microscopy, thermal analysis, synchrotron X-ray diffraction, and hardness testing, a broad preliminary investigation of fundamental alloy properties has been performed, identifying the key areas for further alloy development opportunities.	Nov 2023
I18-Microfocus Spectroscopy	Arsenic and artistry: uncovering secrets in Pietro Lorenzetti's paintings Diamond Light Source Diamond Proposal Number(s): [17644] Show Abstract ▼ Abstract: In 2013, the Ferens Art Gallery in Hull acquired Pietro Lorenzetti's Sienese gold-ground panel Christ between Saints Paul and Peter, a newly discovered example of the Italian artist's work. For four years, the painting underwent intensive conservation treatment and scientific study at The National Gallery in London, revealing vibrant colours and minute details previously obscured by layers of discoloured varnish and earlier conservation efforts. Another of Lorenzetti's works, Virgin and Child Enthroned and Donor, Angels, hangs in the Philadelphia Museum of Art. In work recently published in Studies in Conservation, researchers from the National Gallery and the Natural History Museum in London worked with scientists from Diamond's I18 beamline to analyse samples of mordant gilding taken from both paintings, where previous studies had shown the presence of a mordant tinted with orpiment (a bright yellow mineral pigment containing arsenic) used to adhere overlying layers of silver and gold leaf. Synchrotron microfocus X-ray techniques (SR µ-XANES, µ-XRF and µ-XRD) were used to reveal the chemical migration and nature of altered phases in the orpiment-containing mordant layer. The results add to our understanding of the painting techniques used during this exciting period, and will inform ongoing conservation and restoration efforts.	Nov 2023
I15-Extreme Conditions	Melting line and thermal equation of state of fcc-cobalt: A combined experimental and computational approach Simone Anzellini , Silvia Boccato , Samuel R. Baty , Leonid Burakovsky , Daniele Antonangeli , Daniel Errandonea , Raffaella Torchio Results In Physics 56 DOI: 10.1016/j.rinp.2023.107218 Diamond Proposal Number(s): [21943] Open Access Show Abstract ▼ Abstract: The melting line of cobalt has been investigated both experimentally, using synchrotron X-ray diffraction coupled with laser-heated diamond anvil cells, and theoretically, using ab initio simulations. Over the investigated pressure and temperature range – between 30 and 100 GPa and from ambient temperature up to 4000 K – the hexagonal close-packed structure, stable at ambient conditions, is replaced at high temperature by the face-centered cubic structure, observed stable till melting. The melting temperatures obtained by the two methods are in remarkable agreement and the melting line can be well described by a Simon–Glatzel equation of the form T 1768(K)(P(GPa)/35.62+1) . Finally, from the obtained results it was possible to determine a thermal equation of state for the cubic face-centered phase of Co.	Nov 2023
I11-High Resolution Powder Diffraction	Delayed parabolic oxidation via transient thermal exposures on a polycrystalline nickel-based superalloy J. W. X. Wo , D. M. Collins , M. P. Taylor , M. C. Hardy , H. J. Stone Corrosion Science 47 DOI: 10.1016/j.corsci.2023.111675 Diamond Proposal Number(s): [18972] Open Access Show Abstract ▼ Abstract: Multiple oxides were observed during the transient oxidation stage of the polycrystalline Ni-based superalloy, RR1000, before a protective Cr2O3 scale formed. Thermogravimetric analysis, synchrotron grazing incidence X-ray diffraction, and electron microscopy were performed on samples subjected to isothermal exposures at 800 °C for up to 100 hours. Transient effects governed the early stages up to 40 hours. NiO, spinels (NiCr2O4, (Ni,Co)(Cr,Co)2O4), Cr2O3/(Cr0.88Ti0.12)2O3, NiTiO3, and CrTaO4 formed during the initial stage with pseudo-linear kinetics. At the onset of parabolic kinetics, extensive Cr2O3 and TiO2 growth dominated scale formation with the former emerging as the major passivating oxide.	Nov 2023
	Laser-induced, single droplet fragmentation dynamics revealed through megahertz x-ray microscopy Fabian Reuter , Tokushi Sato , Valerio Bellucci , Sarlota Birnsteinova , Carsten Deiter , Jayanath C. P. Koliyadu , Romain Letrun , Pablo Villanueva-Perez , Richard Bean , Adrian P. Mancuso , Alke Meents , Patrik Vagovic , Claus-Dieter Ohl Physics Of Fluids 35 DOI: 10.1063/5.0171225 Open Access Show Abstract ▼ Abstract: The fragmentation dynamics of single water droplets from laser irradiation is studied with megahertz frame rate x-ray microscopy. Owed to the nearly refraction-free and penetrating imaging technique, we could look into the interior of the droplet and reveal that two mechanisms are responsible for the initial explosive fragmentation of the droplet. First, reflection and diffraction of the laser beam at the droplet interface result in the formation of laser ray caustics that lead to non-homogeneous heating of the droplet, locally above the critical temperature. Second, homogeneous cavitation in the droplet that is likely caused from shockwaves reflected as tension waves at the acoustic soft boundaries of the droplet. Further atomization occurs in three stages, first a fine sub-micrometer sized mist forms on the side of the droplet posterior to laser incidence, then micrometer sized droplets are expelled from the rim of an expanding liquid sheet, and finally into droplets of larger size through hole and ligament formation in the thinning liquid sheet where ligaments pinch off.	Nov 2023

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