Using near-edge x-ray absorption fine structure (NEXAFS) and resonant inelastic x-ray scattering (RIXS) at the C K-edge, we have studied the carbon environment and dynamics in kappa-(BEDT-TTF)2Cu2(CN)3 and supplemented them by density functional theory calculations. The maximum in the NEXAFS pre-edge is identified to originate mainly from nonequivalent carbon sites of the BEDT-TTF molecule, whereas the anionic carbons contribute to the intensity at higher energy. RIXS spectra show resonant reinforcement of the interorbital excitations, but without a clear set of vibrational harmonics, previously detected in our N K-edge RIXS study. This finding points to the strong multimode vibrational excitation of all carbon sites in both (BEDT-TTF)2+ molecular and Cu2(CN)3- anionic subsystems, thus demonstrating a strongly disordered environment which might have important implications for the electronic state of the kappa-(BEDT-TTF)2Cu2(CN)3.

Implementing a newly developed spectrometer for the soft x-ray range of (35-130) eV based on reflection zone plates was successfully accomplished on an electron probe microanalyzer. In this context, we present the first spectra acquired using this setup, including those of elements such as Be (K alpha), C (K alpha), Mg (L2,3), Al (L2,3), and Si (L2,3). We have also conducted an analysis of several lithium compounds and measured the emission of Li K alpha from metallic Li, LiF, and LiNbO3. Some of the results were compared with density functional theory calculations. The spectrum obtained for the lithium-bearing mineral amblygonite Li0.75Na0.25Al(PO4)F0.75(OH)0.25 is chosen to discuss some of the challenges faced.

Hard x‐ray emission spectroscopy (XES) has been used to study buried layers and interfaces in a Fe/Si periodic multilayer. Until now, buried layers could be studied using the XES in the soft x‐ray range. Here, we extend the methodology to study the buried interfaces in hard x‐ray region (photon energy ≥ 5 keV). We report the formation of FeSi2 at all the interfaces with thicknesses of 1.4 nm. X‐ray reflectivity measurements enable us to deduce the structure and thickness of the multilayer stack, thereby confirming the presence of FeSi2.

Lattice dynamics of low-dimensional ${\mathrm{BaVS}}_{3}$ is reported across the metal-insulator Peierls transition occurring at ${T}_{P}=69$ K using a combination of the thermal diffuse scattering of x rays, inelastic x-ray scattering, and density-functional theory calculations. The nondetection of a Kohn anomaly points to a unique situation of an order-disorder Peierls instability with a quasielastic critical scattering which has been fully characterized. These observations are discussed in the scope of a Peierls instability dominated by strong electron-phonon coupling and/or nonadiabatic effects.

Here, the first accurate study is presented of the room-temperature and 100 K structures of one of the first organic spin liquids, κ-(BEDT-TTF)2Ag2(CN)3. It is shown that the monoclinic structure determined previously is only the average one. It is shown that the exact structure presents triclinic symmetry with two non-equivalent dimers in the unit cell. But surprisingly this does not lead to a sizeable charge disproportionation between dimers. The difference from the analogue compound κ-(BEDT-TTF)2Cu2(CN)3 which also presents a spin liquid phase is discussed in detail. The data provided here show the importance of the anionic layer and in particular the transition metal position in the process of symmetry breaking. The possible impact of the symmetry breaking, albeit weak, on the spin-liquid mechanism and the influence of various disorders on the physical properties of this system is also discussed.

V. Ilakovac,1,2,* A. Louat,3,† A. Nicolaou,4,‡ J.-P. Rueff,4,1,§ Y. Joly,5,‖ and V. Brouet3,¶ 1Sorbonne Université, CNRS, Laboratoire de Chimie Physique – Matière et Rayonnement, F-75252 Paris, France 2Département de Physique, Université de Cergy-Pontoise, F-95031 Cergy-Pontoise, France 3Laboratoire de Physique de Solides, CNRS UMR 8502, Univ. Paris Sud, Université Paris Saclay, Orsay, France 4Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, B.P. 48, F-91192 Gif-sur-Yvette, France 5Univ. Grenoble Alpes, CNRS, Institut Néel, Grenoble INP, 38000 Grenoble, France

Iridates are often viewed as an equivalent of cuprates with strong spin-orbit coupling. As such, they offer a new way to study the physics of Mott insulators. The hybridization with oxygen is, of course, essential in both compounds and may play a crucial role in the doping process. It could be quite different in the two families, iridates being 5d transition metals with different orbital geometries. But this difference has not been studied in detail so far. We present a combined angle-resolved photoemission spectrescopy and O K-edge resonant inelastic x-ray scattering study to document this aspect in Sr2IrO4, pure and doped with 4% La and 15% Rh. We evidence different charge transfer excitations and distinguish those associated with apical or in-plane oxygens. We observe a specific evolution of one excitation upon Rh doping, which suggests a more itinerant nature of the holes related to the apical oxygen. This gives information on the way doping proceeds in iridates.

The lattice dynamics of low-dimensional BaVS 3 is reported accross the hexagonal-orthorhombic phase transition occuring at T S = 250 K using a combination of Thermal Diffuse Scattering of X-rays, Inelastic X-ray Scattering and DFT calculations. We observed the occurence of strongly temperature-dependent diffuse scattering upon approaching the transition, centered at the Γ points associated with weak Bragg reflections with odd L. Inelastic scattering experiment related this observation to the condensation of a low-lying overdamped optical phonon at the Brillouin zone center, evidenced by significant variations of quasi-elastic scattering. These results unravel the dynamical origin of the zigzag distortion of the V chains at T S , which is probably a prerequisite of the Peierls anomaly driving the metal-insulator transition at T MI = 70 K

The Kossel effect is the diffraction by a periodically structured medium, of the characteristic X-ray radiation emitted by the atoms of the medium. We show that multilayers designed for X-ray optics applications are convenient periodic systems to use in order to produce the Kossel effect, modulating the intensity emitted by the sample in a narrow angular range defined by the Bragg angle. We also show that excitation can be done by using photons (X-rays), electrons or protons (or charged particles), under near normal or grazing incident geometries, which makes the method relatively easy to implement. The main constraint comes from the angular resolution necessary for the detection of the emitted radiation. This leads to small solid angles of detection and long acquisition times to collect data with sufficient statistical significance. Provided this difficulty is overcome, the comparison or fit of the experimental Kossel curves, i.e., the angular distributions of the intensity of an emitted radiation of one of the element of the periodic stack, with the simulated curves enables getting information on the depth distribution of the elements throughout the multilayer. Thus the same kind of information obtained from the more widespread method of X-ray standing wave induced fluorescence used to characterize stacks of nanometer period, can be obtained using the Kossel effect.

We present here the first accurate determination of the exact structure of κ-(BEDT-TTF)2Cu2(CN)3. Not only did we show that the room temperature structure used over the last twenty years was incorrect, but we were also able to correctly and precisely determine it. The results of our work provide evidence that the structure presents a triclinic symmetry with two non-equivalent dimers in the unit cell, which implies a charge disproportionation between the dimers. However, structural refinement shows that the charge disproportionation is quite weak at room temperature.

Pd/Y multilayers are high-reflectance mirrors designed to work in the 7.5-11 nm wavelength range. Samples, prepared by magnetron sputtering, are deposited with or without B4C barrier layers located at the interfaces of the Pd and Y layers to reduce interdiffusion, which is expected from calculating the mixing enthalpy of Pd and Y. Grazing-incident X-ray reflectometry is used to characterize these multilayers. B4C barrier layers are found to be effective in reducing Pd-Y interdiffusion. Details of the composition of the multilayers are revealed by hard X-ray photoemission spectroscopy with X-ray standing wave effects. This consists of measuring the photoemission intensity from the samples by performing an angular scan in the region corresponding to the multilayer period and an incident photon energy according to Bragg's law. The experimental results indicate that Pd does not chemically react with B nor C at the Pd-B4C interface while Y does react at the Y-B4C interface. The formation of Y-B or Y-C chemical compounds could be the reason why the interfaces are stabilized. By comparing the experimentally obtained angular variation of the characteristic photoemission with theoretical calculations, the depth distribution of each component element can be interpreted.

We use hard x-ray photoemission spectroscopy combined with x-ray standing waves to characterize a series of Pd/Y multilayers designed to work in the 7.5-11 nm wavelength range. The samples, prepared by magnetron sputtering, are deposited either with or without nitrogen introduced in the sputtering gas. The aimed period of the samples is 4 nm. The experiments consist in obtaining the core level spectra of the various elements for a series of grazing angles. The angular scan is made in the range given by the Bragg law, the multilayer period and the incident photon energy. Given the period of the multilayer and the presence of a 2.5 nm-thick B4C capping layer, the photon energy is chosen to be 10 keV in order to probe the first 5-6 periods of the stack. Thus the Bragg angle is a little less than 1 degrees. Rotating the sample enables putting the nodes of the electric field at some particular location of the stack, thus to make the excitation depth-selective, probing one interface or another or the center of one given layer. The changes of the chemical shift in the Pd 2p and 3d, Y 2p and 3d, O 1s, N 1s, C 1s and B 1s as a function of the angle, that is to say as a function of the location in the stack will give information about the possible interfacial process taking place in the Pd/ Y multilayers.

Resonant inelastic x-ray scattering at the N $K$ edge reveals clearly resolved harmonics of the anion plane vibrations in the $\ensuremath{\kappa}$-(BEDT-${\mathrm{TTF})}_{2}{\mathrm{Cu}}_{2}$(${\mathrm{CN})}_{3}$ spin-liquid insulator. Tuning the incoming light energy at the $K$ edge of two distinct N sites permits us to excite different sets of phonon modes. The cyanide (CN) stretching mode is selected at the edge of the ordered N sites which are more strongly connected to the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) molecules, while positionally disordered N sites show multimode excitation. Combining measurements with calculations on an anion plane cluster permits us to estimate the site-dependent electron-phonon coupling of the modes related to nitrogen excitation.

The Kossel interferences generated by characteristic X-ray lines produced inside a periodic multilayer have been observed upon proton irradiation, by submitting a Cr/B4C/Sc multilayer stack to 2MeV protons and observing the intensity of the Sc and Cr Kα characteristic emissions as a function of the detection angle. When this angle is close to the Bragg angle corresponding to the emission wavelength and period of the multilayer, an oscillation of the measured intensity is detected. The results are in good agreement with a model based on the reciprocity theorem. The combination of the Kossel measurements and their simulation, will be a useful tool to obtain a good description of the multilayer stack and thus to study nanometer-thick layers and their interfaces.

A characteristic X-ray line emitted from an atom within a periodic structure can be diffracted by the (emitting) structure itself according to the Bragg law. The subsequent Kossel [1] interferences lead to a modulation of the x-ray line intensity as a function of the detection angle in the vicinity of the Bragg angle value [2]. Standing-wave mechanism and Kossel diffraction can be viewed as space reversed processes by virtue of the reciprocity theorem. Kossel interferences have been yet observed using incident X-ray radiation [3-4], electrons [1-2, 5] and ions [6], in crystals [2,5-6] and in periodic multilayers [2-4]. In the present work, we have studied the characteristic Cr and Sc K emissions produced by a periodic Cr/B4C/S multilayer exposed to a beam of 2 MeV-protons. The period of the multilayer is close to 2 nm. The intensity of these two emission lines is measured as function of the grazing exit angle, i.e. the angle between the direction of the detector and that of the surface of the multilayer. In the case of the Sc K emission, in Figure 1 we compare the experimental results to those calculated combining a classical recursive approach to the reciprocity theorem. To our knowledge, it is the first time that ions are used to induce Kossel diffraction in a multilayer. Refined details about the structure of the stack could be obtained, especially the profile and nature of the interfaces. Figure 1: Measured (red) and calculated (blue) intensity of the Sc K emission as a function of the detection angle. [1] W. Kossel, V. Loeck and H. Voges, Z. Fur Phys. 94, 139 (1935). [2] P. Jonnard P., J.-M. Andre, C. Bonnelle, F. Bridou and B. Pardo, Appl. Phys. Lett. 81 (8), 1524 (2002). [3] J.-P. Chauvineau and F. Bridou, J. Phys. IV 6, C7 (1996). [4] Y. Tu, Y. Yuan, K. Le Guen, J.-M. Andre, J. Zhu, Z. Wang, F. Bridou, A. Giglia and P. Jonnard, J. Synchrotron Radiat. 22, 1419 (2015). [5] V.V. Lider, Crystallogr. Rep. 56, 169 (2011). [6] V. Geist and R. Flagmeyer, Phys. Status Solidi A 26, K1 (1974).

We show that the quasi-1D behavior of BaVS3 can be understood analyzing the X-ray absorption near edge spectra at the sulfur K edge. Linear dichroïsm experiments, analyzed with the help of ab initio calculations, reveal two strong and polarization dependent pre-edge features, induced by the band character of the 3d vanadium levels. They are related to crystal field split t2g and eg states. When the temperature is lowered, the t2g feature shifts progressively to higher energy, and its intensity increases for the polarization along the c-axis, stacking direction of the V–S face sharing octahedra. This behavior points to the depletion of sulfur states and thus the lack of S 3p–V 3d hybridization in the direction of V–S chains.