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Instruments / Technical Area	Publication Details	Published
	Synchrotron radiation techniques and their application to actinide materials R. Caciuffo , G. H. Lander , G. Van Der Laan Reviews Of Modern Physics 95 DOI: 10.1103/RevModPhys.95.015001 Show Abstract ▼ Abstract: Research on actinide materials, both basic and applied, has been greatly advanced by the general techniques available from high-intensity photon beams from x-ray synchrotron sources. The most important single reason is that such x-ray sources can work with minute (e.g., microgram) samples, and at this level the radioactive hazards of actinides are significantly reduced. The form and encapsulation procedures used for different techniques are discussed, followed by the basic theory for interpreting the results. To demonstrate the potential of synchrotron radiation techniques for the study of lattice and electronic structure, hybridization effects, multipolar order, and lattice dynamics in actinide materials, a selection of x-ray diffraction, resonant elastic x-ray scattering, x-ray magnetic circular dichroism, resonant and nonresonant inelastic scattering, dispersive inelastic x-ray scattering, and conventional and resonant photoemission experiments are reviewed.	Mar 2023
I21-Resonant Inelastic X-ray Scattering (RIXS)	Resonant inelastic x-ray scattering from U3O8 and UN Eleanor Lawrence Bright , Lei Xu , Lottie Harding , Ross Springell , Andrew Walters , Martin Sundermann , Mirian Garcia-Fernandez , Stefano Agrestini , Roberto Caciuffo , Gerrit Van Der Laan , Gerry H. Lander Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/acb8f4 Diamond Proposal Number(s): [29274] Show Abstract ▼ Abstract: Resonant inelastic x-ray scattering (RIXS) using an incident energy tuned to the uranium N4,5 absorption edges is reported from epitaxial films of α-U3O8 and UN. Theory shows that for U3O8 the multiplets associated with a 5f1 configuration with a ground state of 2F5/2 and the excited state of 2F7/2 are observed. However, the strong transition predicted at a transfer energy of 1.67 eV is not observed. We assume this is a consequence of the intermediate state lifetime broadening due to interaction with continuum states when the transferred energy exceeds the onset of the continuum in the presence of the core hole. This hypothesis is supported by the results obtained for the 5f-itinerant system UN, where no sharp transitions have been observed, although the broad scattering response centered at ∼ 1 eV is considered a signature of a predominantly 5f3 configuration in this band-like semi-metallic system. These experiments and theory add important information on these materials, both of which have been investigated since the 1960s, as well as whether RIXS at the uranium N edge can become a valuable tool for actinide research.	Feb 2023
I21-Resonant Inelastic X-ray Scattering (RIXS)	X-ray synchrotron radiation studies of actinide materials Roberto Caciuffo , Gerard H. Lander Journal Of Synchrotron Radiation 28 DOI: 10.1107/S1600577521009413 Open Access Show Abstract ▼ Abstract: By reviewing a selection of X-ray diffraction (XRD), resonant X-ray scattering (RXS), X-ray magnetic circular dichroism (XMCD), resonant and non-resonant inelastic scattering (RIXS, NIXS), and dispersive inelastic scattering (IXS) experiments, the potential of synchrotron radiation techniques in studying lattice and electronic structure, hybridization effects, multipolar order and lattice dynamics in actinide materials is demonstrated.	Nov 2021
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
	Transuranium compounds probed by nonresonant inelastic x-ray scattering M. Sundermann , L. Simonelli , S. Huotari , R. Eloirdi , G. H. Lander , R. Caciuffo , G. Van Der Laan Physical Review B 101, 075103 DOI: 10.1103/PhysRevB.101.075103 Show Abstract ▼ Abstract: While x-ray absorption spectroscopy is mainly governed by electric-dipole transitions, the technique of non-resonant inelastic x-ray scattering (NIXS) offers the possibility to explore higher-order multipole transitions. These transitions obey different selection rules that can reach final states of higher angular momenta, opening complementary spectroscopic perspectives. Here, we investigate the suitability of NIXS to study transuranium compounds. We show that the K edge of the Be encapsulation can be practically fully excluded by using the imaging capabilities of the technique arising from the position of the signals on the multidetector. Experimental results for the multipole transitions at the actinide O4,5 edges (90–120 eV) in UO2, NpO2, PuO2, and Pu2O3 are compared with multielectronic calculations. The spectral features are shown to be very sensitive to the ratio of the triakontadipole and octupole transitions, which could potentially be used to assess the radial expansion of the 5f wave function, which is expected to occur in covalent mixing with the O 2p states.	Feb 2020
	Crystal-field states of UO2 probed by directional dependence of nonresonant inelastic x-ray scattering M. Sundermann , G. Van Der Laan , Andrea Severing , L. Simonelli , G. H. Lander , M. W. Haverkort , R. Caciuffo Physical Review B 98, 205108 DOI: 10.1103/PhysRevB.98.205108 Show Abstract ▼ Abstract: Nonresonant inelastic x-ray scattering (NIXS) has been performed on single crystals of UO2 to study the directional dependence of higher-order-multipole scattering from the uranium O4,5 edges (90-110 eV). By comparing the experimental results with theoretical calculations the symmetry of the ground state is confirmed directly as the crystal-field (CF) Γ5 triplet state within the J = 4 manifold. The results demonstrate that the directional dichroism of the NIXS spectra is sensitive to the CF strength and establish NIXS as a tool for probing CF interactions quantitatively.	Nov 2018
Theoretical Physics	TEM-EELS analyses of protactinium O. Dieste , T. Wiss , J.-C. Griveau , R. J. M. Konings , G. Van Der Laan , R. Caciuffo Materials Research Express 6, 026307 DOI: 10.1088/2053-1591/aaef23 Open Access Show Abstract ▼ Abstract: Afragment of metallic protactinium (Pa) has been studied using a transmission electron microscope (TEM) equipped with an electron energy loss spectroscopy (EELS) detector. Bright and dark field TEM images have been acquired, and selective area electron diffraction (SAED) has been used to study the crystal structures. The results showed the presence of domains both of metallic and of oxidized material that likely occurred during sample preparation. EELS edges have been collected for the first time for the oxide compounds and compared with those computed using many-electron atomic spectral methods	Nov 2018
	Absence of superconductivity in fluorine-doped neptunium pnictide NpFeAsO A. C. Walters , H. C. Walker , R. Springell , M. Krisch , A. Bosak , A. H. Hill , C. E. Zvorişte-Walters , E. Colineau , J.-C. Griveau , D. Bouëxière , R. Eloirdi , R. Caciuffo , T. Klimczuk Journal Of Physics: Condensed Matter 27 DOI: 10.1088/0953-8984/27/32/325702 PMID: 26214712 Show Abstract ▼ Abstract: X-ray diffraction, specific heat, magnetic susceptibility and inelastic x-ray scattering measurements on the transurarium oxypnictides NpFeAsO and NpFeAsO0.85F0.15 are presented. No superconductivity down to 2 K was observed upon fluorine doping, contrary to the structurally analogous rare-earth pnictides. No modification of the phonon density of states was observed upon doping with fluorine. We discuss our results in light of the latest experimental and theoretical studies on the role of phonons in the superconducting pnictide compounds.	Aug 2015
I16-Materials and Magnetism	Coherent magnetic diffraction from the uranium M4 edge in the multi-k magnet, USb J. Lim , E. Blackburn , G. Beutier , F. Livet , N. Magnani , A. Bombardi , R. Caciuffo , G. H. Lander Journal Of Physics: Conference Series 519 REXS 2013 — Workshop on Resonant Elastic X-ray Scattering in Condensed Matter DOI: 10.1088/1742-6596/519/1/012010 Diamond Proposal Number(s): [8384] Open Access Show Abstract ▼ Abstract: The slow magnetic dynamics, from seconds to kiloseconds, of the canonical 3-k antiferromagnet USb have been probed, using X-ray photon correlation spectroscopy (XPCS). In this work, XPCS is combined with resonant X-ray diffraction to focus on scattering at an antiferromagnetic Bragg peak. High quality coherent magnetic diffraction patterns were recorded (speckle contrast of about 88%) and magnetic domains were observed; the number of domains increases on warming to T* about 160 K, where the spin waves soften to zero frequency, and again on warming to TN = 218 K. The intensity auto-correlation, g2(t), is primarily static over 1000 s, with a small dynamical process (change of about 0.4%) that increases in rate close to the transitions.	May 2014
I16-Materials and Magnetism	Antiferromagnetism in UO2 thin epitaxial films Z. Bao , R. Springell , H. C. Walker , H. Leiste , K. Kuebel , R. Prang , G. Nisbet , S. Langridge , R. C. C. Ward , T. Gouder , R. Caciuffo , G. H. Lander Physical Review B 88 (13), 341-350 DOI: 10.1103/PhysRevB.88.134426 Show Abstract ▼ Abstract: Thin films (250–4500 Å) of epitaxial UO 2 were produced by reactive sputtering on two different substrate materials: LaAlO 3 and CaF 2 . Using the large enhancement present with resonant x-ray scattering using photons at the uranium M 4 absorption edge, antiferromagnetic (AF) order was found in all films. The ordering temperature T N is the same as the bulk, but the films show second-order (continuous) transitions in contrast to the first-order bulk transition. For LaAlO 3 -based films, an additional strong diffuse magnetic disorder is observed, which is reminiscent of the second-length scale, associated with structural disorder and/or strain. By using a formulation accounting for the strong absorption and coherent nature of the photons, the energy widths at the U M 4 resonances can be related to the thickness of the AF region. The LaAlO 3 -based films do not order magnetically over more than ∼ 600 Å, whereas the CaF 2 -based film orders throughout. Further, for thicker films ( > 1000 Å) the fitting procedure shows that the AF order is located at the top of the LaAlO 3 -based film. This points to the formation in thicker films of a nonmagnetic layer of UO 2 adjacent to the substrate, which may have tetragonal symmetry.	Oct 2013

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