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Electromagnons (Electroactive spin wave excitations) could prove to be decisive in information technologies but they remain fragile quantum objects, mainly existing at low temperatures. Any future technological application requires overcoming these two limitations. By means of synchrotron radiation infrared spectroscopy performed in the THz energy range and under hydrostatic pressure, we tracked the electromagnon in the cupric oxide CuO, despite its very low absorption intensity. We demonstrate how a low pressure of 3.3 GPa strongly increases the strength of the electromagnon and expands its existence to a large temperature range enhanced by 40 K. Accordingly, these two combined effects make the electromagnon of CuO under pressure a more ductile quantum object. Numerical simulations based on an extended Heisenberg model were combined to the Monte-Carlo technique and spin dynamics to account for the magnetic phase diagram of CuO. They enable to simulate the absorbance response of the CuO electromagnons in the THz range.

This paper presents a study of the lattice dynamics in BaFe

Relativistic electron bunches used in synchrotron light sources are complex media, in which patterns might form spontaneously. These spatial structures were studied over the past decades for very practical reasons. The patterns, which spontaneously appear during an instability, increase the terahertz radiation power by factors exceeding 10,0001,2. However, their irregularity1–7 largely prevented applications of this powerful source. Here we show that principles from chaos control theory8–10 allow us to generate regular spatio-temporal patterns, stabilizing the emitted terahertz power. Regular unstable solutions are expected to coexist with the undesired irregular solutions, and may thus be controllable using feedback control. We demonstrate the stabilization of such regular solutions in the Synchrotron SOLEIL storage ring. Operation of these controlled unstable solutions enables new designs of high-charge and stable synchrotron radiation sources. A feedback loop based on chaos control theory permits the generation of stable and coherent terahertz radiation from relativistic electron bunches in synchrotron light sources.

We report in this paper the dynamical properties of ${\mathrm{GdMn}}_{2}{\mathrm{O}}_{5}$ studied by inelastic neutron scattering and infrared spectroscopy assisted by ab initio calculations. Our work sheds light on the electromagnon, a magnetic mode that can be excited by an electric field. Combining spin-wave measurements, simulations, and ab initio calculations of the single-ion anisotropies and the superexchange interactions, we describe in detail the magnetic contribution to this mode. An exhaustive study of the temperature and polarization dependence of its electroactivity completes this comprehensive study of the complex ${\mathrm{GdMn}}_{2}{\mathrm{O}}_{5}$ system.

Magnetic and crystallographic transitions in the Cairo pentagonal magnet ${\mathrm{Bi}}_{2}{\mathrm{Fe}}_{4}{\mathrm{O}}_{9}$ are investigated by means of infrared synchrotron-based spectroscopy as a function of temperature (20--300 K) and pressure (0--15.5 GPa). One of the phonon modes is shown to exhibit an anomalous softening as a function of temperature in the antiferromagnetic phase below 240 K, highlighting spin-lattice coupling. Moreover, under applied pressure at 40 K, an even larger softening is observed through the pressure-induced structural transition. Lattice dynamical calculations reveal that this mode is indeed very peculiar as it involves a minimal bending of the strongest superexchange path in the pentagonal planes, as well as a decrease in the distances between second-neighbor irons. The latter confirms the hypothesis made by Friedrich et al., [J. Phys.: Condens. Matter 24, 145401 (2012)] about an increase in the oxygen coordination of irons being at the origin of the pressure-induced structural transition. As a consequence, one expects a new magnetic superexchange path that may alter the magnetic structure under pressure.

Organo-lead halide perovskites are nowadays considered to be an emerging photovoltaic material. It is clear that the peculiar hybrid nature of this class of materials is central for their outstanding optical and transport properties. However, the role of the organic cation and its interplay with the inorganic framework remains elusive. To get insight into the interactions at play, high-pressure Raman, infrared, and X-ray absorption spectroscopy measurements were performed on MAPbBr3 (MA = CH3NH3+). Since lattice compression allows for a fine-tuning of the organic/inorganic interaction, we were able to follow the pressure evolution of the MA dynamics within the PbBr6 cage and identify different phases. From a MA dynamical disordered configuration, the system enters at first a cation ordered phase and, at higher pressure, a static disordered MA phase. Data analysis points at H-bonding as the driving force for molecular reorientation. Since the MA dynamics directly influence the formation of polarons in hybr...

International audience; Keywords: Ferroelectricity Thin films Silicon Epitaxy Radio-frequency magnetron sputtering Infrared spectroscopy Phonon A B S T R A C T BaTiO 3 thin films (60 nm-thick) grown on SrTiO 3 /Si templates have been characterized for their structural and electrical properties. The epitaxy of the BaTiO 3 film on silicon was confirmed by X-ray diffraction with good crystallinity. The temperature-dependent structural properties were checked by infrared spectroscopy in absorption mode. The films were found to remain in a single ferroelectric phase over a temperature range from 5 to 385 K. Low-temperature orthorhombic-rhombohedral phase transitions characteristic of bulk BaTiO 3 are absent in the films due to the clamping effect from the Si substrate.

His/Cys coordination was recently found in several c-type cytochromes, which could act as sensors, in electron transport or in regulation. Toward a better understanding of Cys function and reactivity in these cytochromes, we compare cytochrome c6 (c6wt) from the cyanobacterium Nostoc PCC 7120 with its Met58Cys mutant. We probe the axial ligands and heme properties by combining visible and mid- to far-FTIR difference spectroscopies. Cys58 determines the strong negative redox potential and pH dependence of M58C (EmM58C = -375 mV, versus Emc6wt = +339 mV). Mid-IR (notably Cys ν(SH), His ν(C5N1), heme (CmH)) and far-IR (ν(Fe(II)-His), ν(His-Fe(III)-Cys)) markers of the heme and ligands show that Cys58 remains a strong thiolate ligand of reduced Met58Cys at alkaline pH, while it is protonated at pH 7.5, is stabilized by a strong hydrogen bonding interaction, and weakly interacts with Fe(II). These data provide a benchmark for further analysis of c-type cytochromes with natural His/Cys coordination French Agence Nationale de la Recherche (ANR) PSIIFIR ANR-15-CE05-0016 French Infrastructure for Integrated Structural Biology (FRISBI) ANR-10-INBS-05 Ministerio de Ciencia e Innovación PGC2018-096049-B-I00 Junta de Andalucía BIO-198, US-1257019, US-1254317

The low-energy lattice dynamics of the quasiperiodic spin-ladder cuprate ${\mathrm{Sr}}_{14\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ are investigated using terahertz frequency synchrotron radiation. A high density of low-lying optical excitations is present in the 1--3 THz energy range, while at least two highly absorbing excitations stemming from long-wavelength acoustic oscillations of the incommensurate chain and ladder sublattices, are observed at subterahertz frequencies. The effects of Ca substitution on the subterahertz quasiacoustic sliding mode gaps is investigated using coherent synchrotron radiation. Analysis of the results suggest increasing substitution of Sr for Ca is accompanied by a transfer of spectral weight between sliding modes associated with different chain-ladder dynamics. The observation is consistent with a transfer of hole charges from the chains to the ladders and modification of the sublattice dimensions following Ca substitution. The results are discussed in context to the significance of low-lying vibrational dynamics and electron-phonon coupling in the superconducting state of certain quasiperiodic systems.

We present recent results on the characterization and control of the coherent terahertz pulses emitted by synchrotron radiation facilities. We first show novel ultrafast single-shot measurements techniques now allow these sources to be fully characterized in a pulse-by-pulse basis [1]. Then we present a novel feedback method that enables the dynamics of these sources to be fully controlled [2]. This opens the way to novel sources of stable THz radiation, and to high repetition-rate spectroscopic applications.

International audience; Abstract:Optical probes are among the most important techniques for characterizing new physical states induced by changes of temperature and/or pressure. In link with its high brightness and wide spectral coverage, infrared synchrotron radiation is ideally suited for such studies when the quantity of material to investigate is limited or when the system needs to be probed down to the sub mm domain.

International audience; A groundbreaking discovery in nanofluidics was the observation of the tremendously enhanced water permeability of carbon nanotubes, those iconic objects of nanosciences. The origin of this phenomenon is still a subject of controversy. One of the proposed explanations involves dramatic modifications of the H-bond network of nanoconfined water with respect to that of bulk water. Infrared spectroscopy is an ideal technique to follow modifications of this network through the inter- and intramolecular bonds of water molecules. Here we report the first infrared study of water uptake at controlled vapor pressure in single walled carbon nanotubes with diameters ranging from 0.7 to 2.1 nm. It reveals a predominant contribution of loose H bonds even for fully hydrated states, irrespective of the nanotube size. Our results show that, while the dominating loosely bond signature is attributed to a one-dimensional chain structure for small diameter nanotubes, this feature also results from a water layer with “free” OH (dangling) bonds facing the nanotube wall for larger diameter nanotubes. These experimental findings provide a solid reference for further modeling of water behavior in hydrophobic nanochannels.

International audience; In the multiferroic hexagonal manganite HoMnO3, inelastic neutron scattering and synchrotron based THz spectroscopy have been used to investigate the spin waves associated to the Mn order together with Ho crystal field excitations. While the Mn order sets in first below 80 K, a spin reorientation occurs below 37 K, a rare feature in the rare earth manganites. We show that several Ho crystal field excitations are present in the same energy range as the magnons, and that they are all affected by the spin reorientation. Moreover, several anomalous features are observed in the excitations at low temperature. Our analysis and calculations for the Mn spin waves and Ho crystal field excitations support Mn-Ho coupling mechanisms as well as coupling to the lattice affecting the dynamics.

We report on the characteristics of coherent synchrotron radiation (CSR) as a source for spectroscopy. The optimization of the source and the resulting figures of merits in terms of flux, signal to noise, spatial distribution and spectral and temporal distribution are presented together with a spectroscopic application. The emission of THz during the slicing operation is also described. The conclusion opens up perspectives made possible by the availability of this intense and stable THz source.

The discovery of a superconducting phase in sulfur hydride under high pressure with a critical temperature above 200 K has provided fresh impetus to the search for superconductors at ever higher temperatures. Although this systems displays all the hallmarks of superconductivity, the mechanism through which it arises remains to be determined. Here we provide a first optical spectroscopy study of this superconductor. Experimental results for the optical reflectivity of H3S, under hydrostatic pressure of 150 GPa, for several temperatures and over the range 60 to 600 meV of photon energies, are compared with theoretical calculations based on Eliashberg theory. Two significant features stand out: some remarkably strong infrared active phonons at around 160 meV, and a band with a depressed reflectance in the superconducting state in the region from 450 meV to 600 meV. In this energy range H3S becomes more reflecting with increasing temperature, a change that is traced to superconductivity originating from the electron-phonon interaction. The shape, magnitude, and energy dependence of this band at 150 K agrees with our calculations. This provides strong evidence of a conventional mechanism. However, the unusually strong optical phonon suggests a contribution of electronic degrees of freedom.

International audience; Due to their narrow and well-defined structure, single wall nanotube, aluminosilicate nanotubes (imogolites) are excellent candidates to study how water is modified by either confinement or by the interface nature. A protocol is provided here to produce imogolite films that are ideally suited for infrared studies. Two types of imogolites were selected: a hydrophilic imogolite (IMO-OH) with inner surface fully covered with Si–OH hydrophilic groups and a hybrid imogolite (IMO-CH 3) with inner surface fully covered with hydrophobic Si–CH 3 groups. Films with different thicknesses were characterized by Small Angle X-ray Scattering (SAXS). The initial water content and the porosity of the films were estimated from ThermoGravimetric Analysis (TGA). Infrared spectroscopy was used to deduce the molar absorption coefficient of the bending mode that is significantly modified in confined water as compared to bulk water. Moreover, the interest of these films which allow avoiding extra-absorption features from the salt matrix or the supporting wafer is illustrated by an infrared study of the processes occurring in the IMO-OH film when it is heated from room temperature up to 350 °C. The evolution of the IR bands while heating shows the dehydration/dehydroxylation processes.

International audience; Chalcogenide alloys in the Ag2SAs2S3HgI2 pseudo-ternary system were synthesized and their vitreous nature was verified by X-ray diffraction. The glass transition and crystallization temperatures (Tg and Tc), the density (d), and the total electrical conductivity (σ) were measured for all samples of three series, A, B, and C corresponding to (Ag2S)50−x/2(As2S3)50−x/2(HgI2)x, (Ag2S)y(As2S3)80−y(HgI2)20 and (Ag2S)z(As2S3)50(HgI2)50−z, respectively. The maximum of Tg was approximately 160 °C for glasses with low HgI2 content whereas the maximum of density (5.75 g.cm−3) was obtained for the sample in the B-series with the highest Ag2S concentration (z=60 mol. %). This composition also possesses the highest conductivity at 298 K (σ298K≈10−3 S.cm−1). Unexpectedly the conductivity of the A-series samples was observed to decrease as a function of the Ag2S content. The far-infrared transmission in the 100 cm−1-600 cm−1 window range (3.3 THz-18.2 THz, 100 µm-16.6 µm) was also given for a few glass compositions highlighting the strong influence of the HgI2 content.

A detailed investigation of the phase diagram of the mixtures of the two ionic liquids N-trimethyl-N-propylammonium bis(trifluoromethylsulfonyl)imide (TMPA-TFSI) and N-trimethyl-N-hexylammonium bis(trifluoromethylsulfonyl)imide (TMHA-TFSI) has been performed in the temperature range between 140 and 330 K by means of DSC and infrared spectroscopy measurements. In the low temperature crystalline states, a large concentration of trans-TFSI conformer is present in TMPA-TFSI, while almost only cis-TFSI is retained in TMHA-TFSI. For the mixtures (TMPA-TFSI)100-x (TMHA-TFSI)x, at concentrations close to the extremes, solid crystalline phases are still present and they show a strong predominance of the trans conformer of the TFSI ion for x < 15 or a large concentration of the cis conformer of TFSI for x > 85. At intermediate concentrations (33 < x < 67) no crystalline phase develops at low temperatures and both conformers of TFSI survive in the whole temperature range here investigated. We suggest that the competition between the two TFSI conformers at low temperatures can be the origin of the lack of crystalline phases for intermediate concentrations and can be exploited as a valid tool to tailor the physical properties of the mixtures of ionic liquids.

Context. To model the cold dust emission observed in the diffuse interstellar medium, in dense molecular clouds or in cold clumps that could eventually form new stars, it is mandatory to know the physical and spectroscopic properties of this dust and to understand its emission. Aims. This work is a continuation of previous studies aiming at providing astronomers with spectroscopic data of realistic cosmic dust analogues for the interpretation of observations. The aim of the present work is to extend the range of studied analogues to iron-rich silicate dust analogues. Methods. Ferromagnesium amorphous silicate dust analogues were produced by a sol-gel method with a mean composition close to Mg1−xFexSiO3 with x = 0.1, 0.2, 0.3, 0.4. Part of each sample was annealed at 500 °C for two hours in a reducing atmosphere to modify the oxidation state of iron. We have measured the mass absorption coefficient (MAC) of these eight ferromagnesium amorphous silicate dust analogues in the spectral domain 30−1000 μm for grain temperature in the range 10−300 K and at room temperature in the 5−40 μm range. Results. The MAC of ferromagnesium samples behaves in the same way as the MAC of pure Mg-rich amorphous silicate samples. In the 30−300 K range, the MAC increases with increasing grain temperature whereas in the range 10−30 K, we do not see any change of the MAC. The MAC cannot be described by a single power law in λ− β. The MAC of the samples does not show any clear trend with the iron content. However the annealing process has, on average, an effect on the MAC that we explain by the evolution of the structure of the samples induced by the processing. The MAC of all the samples is much higher than the MAC calculated by dust models. Conclusions. The complex behavior of the MAC of amorphous silicates with wavelength and temperature is observed whatever the exact silicate composition (Mg vs. Fe amount). It is a universal characteristic of amorphous materials, and therefore of amorphous cosmic silicates, that should be taken into account in astronomical modeling. The enhanced MAC of the measured samples compared to the MAC calculated for cosmic dust model implies that dust masses are overestimated by the models.

When studying magnetic excitations, neutron spectroscopy is typically the method of choice. The low-energy and electromagnetic nature of terahertz radiation presents a new and complementary technique to probe exotic magnetic states. Here we perform terahertz spectroscopy on the quantum spin-ice candidate Tb 2 Ti 2 O 7 using standard and coherent synchrotron radiation. These novel measurements show fine structure and polarization dependent features that reveal new information about a possible vibronic ground state in Tb 2 Ti 2 O 7 and are complementary to existing neutron studies.

Optical measurements were carried out by infrared spectroscopy on AA′3B4O12 A-site ordered quadruple perovskite EuCu3Fe4O12 (microscopic sample) as function of temperature. At 240 K (=TMI), EuCu3Fe4O12 undergoes a very abrupt metal to insulator transition, a paramagnetic to antiferromagnetic transition and an isostructural transformation with an abrupt large volume expansion. Above TMI, optical conductivity reveals a bad metal behavior and below TMI, an insulating phase with an optical gap of 125 meV is observed. As temperature is decreased, a large and abrupt spectral weight transfer toward an energy scale larger than 1 eV is detected. Concurrently, electronic structure calculations for both high and low temperature phases were compared to the optical conductivity results giving a precise pattern of the transition. Density of states and computed optical conductivity analysis identified Cu3dxy, Fe3d and O2p orbitals as principal actors of the spectral weight transfer. The present work constitutes a first step to shed light on EuCu3Fe4O12 electronic properties with optical measurements and ab-initio calculations.

International audience; In recent synchrotron radiation facilities, the use of short (picosecond) electron bunches is a powerful method for producing giant pulses of terahertz coherent synchrotron radiation. Here we report on the first direct observation of these pulse shapes with a few picoseconds resolution, and of their dynamics over a long time. We thus confirm in a very direct way the theories predicting an interplay between two physical processes. Below a critical bunch charge, we observe a train of identical THz pulses (a broadband Terahertz comb) stemming from the shortness of the electron bunches. Above this threshold, a large part of the emission is dominated by drifting structures, which appear through spontaneous self-organization. These challenging single-shot THz recordings are made possible by using a recently developed photonic time stretch detector with a high sensitivity. The experiment has been realized at the SOLEIL storage ring.

International audience; Absorbance spectra of two ionic liquids, the short alkyl chain N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) imide (TMPA-TFSI) and the longer chain N-trimethyl-N-hexylammonium bis(trifluoromethanesulfonyl)imide (TMHA-TFSI) are reported as a function of pressure and temperature. The occurrence of various phase transitions is evidenced by the changes in the relative concentration of the cisoid and transoid conformers of their common TFSI anion. The infrared spectrum of TMPA-TFSI was measured at 300 K with an applied pressure varying over the 0-5 GPa range. Above 0.2 GPa only the trans conformer is detected, suggesting the occurrence of a pressure induced crystallization. When pressure is applied to TMHA-TFSI at T = 310 K, both TFSI conformers subsist up to similar to 11 GPa. However, the clear change of their intensity ratio observed around 2 GPa, suggests the onset of a glass phase as supported by measurements carried out at 4.2 GPa along a cooling/heating cycle. A careful analysis of the spectra collected along different p-T thermodynamic paths shows the occurrence of a cold crystallization at 295 K on heating from 139 K along the p = 0.5 GPa isobar. The rich phase diagrams of the two ionic liquids is the result of the competition among the anion cation intermolecular interactions, the lower energy of trans-TFSI with respect to cis-TFSI and the smaller volume of cis-TFSI with respect to trans-TFSI.

We present here the latest results from experimental studies aiming at measuring the Mass Absorption Coefficient (MAC) of interstellar silicate dust analogues at low temperatures in the far infrared and submillimetre domains which are necessary for the analysis of astronomical data. These results show that above 100 μ m, the MAC of amorphous silicate nano-grains has a complex dependence with the grain temperature and with the wavelength. This has to be considered when interpreting astronomical observations to avoid errors on the derived parameters such as the dust mass and its physical and chemical properties.

During high temperature oxidation of alumina-forming alloys, various transition aluminas are formed before reaching the most stable alpha-Al{sub 2}O{sub 3} phase. In particular, the gamma, delta and theta transition aluminas are concerned. Precise studies on the development, the microstructure and the properties of the oxide layers are not straightforward owing to the difficulty to unambiguously distinguish the various polymorphs by X-ray diffraction (XRD) alone. To remove this difficulty, we propose a procedure which combines XRD and infrared (IR) spectroscopy. gamma, delta, theta and alpha-Al{sub 2}O{sub 3} phases, prepared by dehydration of aluminium oxihydroxide AlOOH (boehmite), were measured by XRD and IR spectroscopy on all samples. Thus, reference IR spectra were obtained for all alumina phases, as well as an assignment of the main band in agreement with previous studies, and coherent with the structural evolution of various polymorphs. This precise characterization may constitute a basis for further investigations on thin layers of alumina formed under various experimental conditions (temperature, atmosphere, etc.). - Graphical abstract: Infrared spectra of alumina sequence gamma->delta->theta->alpha-Al{sub 2}O{sub 3} obtained from 24h calcinations of boehmite at 873 K (a), 1123K (b), 1223 K (c), 1273 K (d), 1293 K (e), 1383 K (f), 1573 K (g).

Physical and thermal properties of glyceryl behenate (Compritol 888 ATO) used as sustained-release matrix in pharmaceutical applications are studied by coupled time-resolved synchrotron X-ray diffraction and Differential Scanning Calorimetry combined with Infrared Spectroscopy. With these techniques, all polymorphs formed in glyceryl behenate, analyzed as received and after various thermal treatments from quenching to slow crystallization, are characterized. By using different well-controlled mixtures of mono-, di- and tribehenate, we identify each lamellar phase observed in the glyceryl behenate. Finally the influence of the crystallization rate on the formation of preferential conformations was also analyzed in order to bring insights into the polymorphism of glyceryl behenate. By changing the crystallization rate of the sample, it was shown that one can favor the formation of preferential polymorphs in the sample. In particular the crystallization at 10 degrees C/min seems to be well adapted for producing a single lamellar phase with a period of 60.9 A while a crystallization rate of 0.4 degrees C/min produces three different lamellar phases.

We consider the problem of shot-by-shot acquisition of pulse shapes at high repetition rate in accelerator-basedsystems. More speci cally, we examine the two-step strategy consisting in (i) encoding the pulse information ontoa laser pulse, and (ii) use the so-called time-stretch strategy to \slow-down" the information before recording.We thus show that the repetition rate of already existing electro-optic sampling setups can be straightforwardlyincreased up to the 100 10 6 pulses/s range, and make a demonstration for the detection of coherent THz pulses.The strategy is however not limited to electro-optic sampling of THz pulses or electron bunches. It can be appliedto other types of wavelengths, provided the desired information (as e.g., FEL pulses or electron bunches shapes)can be imprinted onto a laser pulse.Keywords: Coherent Synchrotron Radiation, Electro-optic sampling, Photonic time-stretch, Terahertz optics 1. INTRODUCTION In accelerator-based coherent sources, there is a growing need for pulse shape characterization at high repetitionrates. High repetition rates is encountered in existing Free-Electron Lasers (FEL), when the emission is composedof bursts of pulses at multi-MHz repetition rates.

Physical and thermal properties of polyoxyethylene glycol glycerides (Gelucire 50/13) used as sustained-release matrix forming agent in pharmaceutical applications are studied by coupled time-resolved synchrotron X-ray diffraction and differential scanning calorimetry combined with infrared spectroscopy. With these techniques, all polymorphs formed after various thermal treatments from quenching to slow crystallization are characterized. In particular, the fatty esters of polyoxyethylene glycol (PEG) polymorph conformations are all provided by the same lamellar phase with the PEG chains under a helical conformation but with a more or less important tilt of the PEG chains. The rate of crystallization was crucial for the formation of these polymorphs. A slow crystallization rate (0.1 °C/min) will induce the formation of a 120 A lamellar phase presenting a higher melting point and consequently a better stability in time and in temperature. Inversely, a rapid crystallization rate will induce the formation of a 90 A lamellar phase. We show, however, the possibility of a rapid transition toward the most stable form. Possible interdigitation of fatty acid chains is also discussed.

Both X-ray diffraction and infrared spectroscopy on water confined between the lamellar bilayers of aerosol-OT (AOT) allowed us to explore the differences in connectivity between bulk and confined water when water layer thicknesses are allowed to vary from 19.0 to 1.5 nm. Compared with previous studies on AOT reverse micelles, the present report in the lamellar mesophase allows one to cancel the micelle curvature contribution, which disrupts the water connectivity, too. The influence of AOT surface on the water connectivity degree was thus quantified alone in the mid infrared region (3000−3800 cm-1) in the OH stretching mode. The OH stretching mode peak can be fitted by three Gaussian peaks that describe three main connecting populations, namely the “multimer” water at c.a. 3585 cm-1, the “intermediary” water at c.a. 3465 cm-1, and the “network” water at c.a. 3320 cm-1. It is shown that interactions with the surfactant heads do not alter the water structure until the water layer shrinks below 4.0 nm and t...

Three ensembles designed to investigate condensed matter in complex environments have been developed recently on the AILES beamline at SOLEIL. They have been exploited for studies aiming at understanding the properties of water molecules and their network in various confining systems, namely: - a hydration and temperature-controlled cell for the study of water confined in nanoporous Vycor, - a high pressure set-up allowing the study of the evolution of water molecules network trapped in Faujasite through the pressure-induced amorphisation of the matrix material, - a temperature resolved electrochemical cell used to record FIR difference spectra of metalloproteins interacting with water molecules. By combining the high infrared flux and collimation of the AILES beamline with these optimized sample environments, it is possible to measure the infrared and THz spectra for minute quantities of samples in precise physical conditions.

International audience; Water–ions interactions and spatial confinement largely determine the properties of hydrogen-bonded nanomaterials. Hydrated acidic polymers possess outstanding proton-conducting properties due to the interconnected H-bond network that forms inside hydrophilic channels upon water loading. We report here the first far-infrared (FIR) coupled to mid-infrared (MIR) kinetics study of the hydration mechanism in benchmark perfluorinated sulfonic acid (PFSA) membranes, e.g., Nafion. The hydration process was followed in situ, starting from a well-prepared dry state, within unprecedented continuous control of the relative humidity. A step-by-step mechanism involving two hydration thresholds, at respectively λ = 1 and λ = 3 water molecules per ionic group, is assessed. The molecular environment of water molecules, protonic species, and polar groups are thoroughly described along the various states of the polymer membrane, i.e., dry (λ ≈ 0), fully ionized (λ = 1), interacting (λ = 1–3), and H-bonded (λ > 3). This unique extended set of IR data provides a comprehensive picture of the complex chemical transformations upon loading water into proton-conducting membranes, giving insights into the state of confined water in charged nanochannels and its role in driving key functional properties as ionic conduction.

International audience; Solutions containing 8 and 32 wt% myoglobin are studied by means of infrared spectroscopy, as a function of temperature (290 K and lower temperatures), in the mid- and far-infrared spectral range. Moreover, ultrafast time-resolved infrared measurements are performed at ambient temperature in the O-D stretching region. The results evidence that the vibrational properties of water remain the same in these myoglobin solutions (anharmonicity, vibrational relaxation lifetime...) and in neat water. However, the collective properties of the water molecules are significantly affected by the presence of the protein: the orientational time increases, the solid-liquid transition is affected in the most concentrated solution and the dynamical transition of the protein is observed, from the point of view of water, even in the least concentrated solution, proving that the water and myoglobin dynamics are coupled.

The low-energy dynamical properties of the multiferroic hexagonal perovskite ErMnO3 have been studied by inelastic neutron scattering as well as terahertz and far infrared spectroscopies on a synchrotron source. From these complementary techniques, we have determined the magnon and crystal field spectra and identified a zone center magnon excitable only by the electric field of an electromagnetic wave. Using a comparison with the isostructural YMnO3 compound and crystal field calculations, we propose that this dynamical magnetoelectric process is due to the hybridization of a magnon with an electroactive crystal field transition.

Water confined in non-ionic fluorocarbon reverse micelles was investigated through infrared spectroscopy. The characteristic OH stretching band is seen to exhibit significant changes upon growing water core size. An analysis in terms of three gaussians, each of which being ascribed to different water type molecules is performed. From a comparison with ionic systems, it is found that the presence of counterions is not a major factor in the perturbation of water connectivity, thus suggesting that the size of confinement prevails.

The low-energy dynamical properties of the multiferroic hexagonal perovskite ErMnO3 have been studied by inelastic neutron scattering as well as terahertz and far infrared spectroscopies on a synchrotron source. From these complementary techniques, we have determined the magnon and crystal field spectra and identified a zone center magnon excitable only by the electric field of an electromagnetic wave. Using a comparison with the isostructural YMnO3 compound and crystal field calculations, we propose that this dynamical magnetoelectric process is due to the hybridization of a magnon with an electroactive crystal field transition.

The infrared absorption spectra of two ionic liquids with bis(trifluoromethanesulfonyl)imide (TFSI) as an anion and ammonium with different alkyl chains as cations are reported as a function of temperature. Using the comparison with ab initio calculations of the infrared-active intramolecular vibrations, the experimental lines were ascribed to the various ions composing the ionic liquids. In the liquid state of the samples, both conformers of the TFSI ion are present. In the solid state, however, the two conformers survive in N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI), while only cis-TFSI is retained in N-trimethyl-N-hexylammonium bis(trifluoromethanesulfonyl)imide (TMHA-TFSI). We suggest that the longer alkyl chains of the former compound stabilize the less stable conformer of TFSI by means of stronger interactions between anions and cations.

Emission of light by a single electron moving on a curved trajectory (synchrotron radiation) is one of the most well-known fundamental radiation phenomena. However experimental situations are more complex as they involve many electrons, each being exposed to the radiation of its neighbors. This interaction has dramatic consequences, one of the most spectacular being the spontaneous formation of spatial structures inside electrons bunches. This fundamental effect is actively studied as it represents one of the most fundamental limitations in electron accelerators, and at the same time a source of intense terahertz radiation (Coherent Synchrotron Radiation, or CSR). Here we demonstrate the possibility to directly observe the electron bunch microstructures with subpicosecond resolution, in a storage ring accelerator. The principle is to monitor the terahertz pulses emitted by the structures, using a strategy from photonics, time-stretch, consisting in slowing-down the phenomena before recording. This opens the way to unpreceeded possibilities for analyzing and mastering new generation high power coherent synchrotron sources., Comment: 7 pages, 6 figures

a b s t r a c t We measured the far- and mid-infrared spectra of three ionic liquids having bis(trifluoromethanesulfonyl)imide anions and three different cations of the families of pyrroli- dinium and ammmonium ions. The molecular vibrations of the individual ions were calculated by means of DFT theory at the B3LYP/6-31G** level: we found good agreement between the experimental and the computed frequencies. The infrared lines are ascribable to molecular vibrations of the single ions, suggesting an extremely weak interaction between anions and cations. The spectral lines found experimentally between 760 and 1050 cm−1 are fingerprints for different cations. The comparison with the calculated frequencies allows the assignment of the experimental spectral lines to specific molecular vibrations of anions and for the first time of the specific cations of the measured ionic liquids. © 2014 Elsevier B.V. All rights reserved.

We report on the first simultaneous observations of both electronic and structural temperature-induced insulator-to-metal transition (IMT) in VO2 ultrathin films, made possible by the use of broad range transmission infrared spectroscopy. Thanks to these techniques, the infrared phonon structures, as well as the appearance of the free carrier signature, were resolved for the first time. The temperature-resolved spectra allowed the determination of the temperature hysteresis for both the structural (monoclinic-to-rutile) and electronic (insulator-to-metallic) transitions. The combination of these new observations and DFT simulations for the monoclinic structure allows us to verify the direct transition from monoclinic (M1) to rutile and exclude an intermediate structural monoclinic form (M2). The delay in structural modification compared to the primer electronic transition (325 K compared to 304 K) supports the role of free charges as the transition driving force. The shape of the free charge hysteresis suggests that the primer electronic transition occurs first at 304 K, followed by both its propagation to the heart of the layer and the structural transition when T increases. This study outlines further the potential of VO2 ultrathin films integrated on silicon for optoelectronics and microelectronics.

We present the first high resolution (10-3 cm(-1)) interferometric measurements in the 200-750 GHz range using coherent synchrotron radiation, achieved with a low momentum compaction factor. The effect of microbunching on spectra is shown, depending on the bunch current. A high signal-tonoise ratio is reached thanks to an artifact correction system based on a double detection scheme. Combined to the broad emitted spectral range and high flux (up to 10(5) times the incoherent radiation), this study demonstrates that coherent synchrotron radiation can now be used for stability-demanding applications, such as gas-phase studies of unstable molecules. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793558]

We have determined the terahertz spectrum of the chiral langasite Ba3NbFe3Si2O14 by means of synchrotron-radiation measurements. Two excitations are revealed that are shown to have a different nature. The first one, purely magnetic, is observed at low temperature in the magnetically ordered phase and is assigned to a magnon. The second one persists far into the paramagnetic phase and exhibits both an electric and a magnetic activity at slightly different energies. This magnetoelectric excitation is interpreted in terms of atomic rotations and requires a helical electric polarization.

International audience; Following our recent study devoted to measurements of intensities of pure rotation lines of methane, room temperature far infrared spectra of methane diluted in nitrogen at five total pressures between 100 and 800 hPa have been recorded at the AILES beamline of the SOLEIL synchrotron. One hundred and five N-2 broadening coefficients of methane pure rotation lines have been measured in the 83-261 cm(-1) spectral range using multi-spectrum non-linear least squares fitting of Voigt profiles. Pressure-induced line shifts were not needed to fit the spectra to the noise level and line mixing effects were neglected. One hundred and seventy-six self broadening coefficients have also been measured in the 59-288 cm(-1) spectral range using the pure methane spectra recorded in our previous work. The measured N-2 broadening coefficients were compared to semi-classical calculations.

The work reports the direct epitaxial growth of SrTiO 3 on Si (001) substrate by molecular beam epitaxy. The impact of the growth temperature and the initial oxygen partial pressure on the heteroepitaxy is studied in detail using different in-situ and ex-situ characterization methods. The optimal growth condition has been identified as 360 °C with the initial oxygen partial pressure of 5 × 10 − 8 Torr to achieve a high-quality single crystalline SrTiO 3 film and a coherent interface between SrTiO 3 and Si. The THz Infrared (IR) measurements show that the biaxial strained SrTiO 3 commensurately grown on silicon undergoes a cubic–tetragonal phase transition.

International audience; As a tetrahedral molecule, methane has no permanent dipole moment. Its spectrum, however, displays faint absorption lines in the THz region, due to centrifugal distorsion effects. This is important for planetary applications since this region is used to measure methane concentration in some planetary atmospheres, in particular on Titan. Up to now, all measurements relied either on some old low resolution infrared absorption spectra, or on high resolution Stark measurements for low J values only. Even if these results have been reexamined recently [E. H. Wishnow, G. S. Orton, I. Ozier and H. P. Gush, J. Quant. Spectrosc. Radiat. Transfer 103, 102-117 (2007)], it seemed highly desirable to obtain much more precise laboratory data. The high-intensity synchrotron radiation, combined with a 151.75 +/- 0.1 m optical path in a White cell and a Bruker IFS 125 HR FTIR spectrometer at the AILES beamline of SOLEIL, enabled us to record this very weak spectrum at high resolution for the first time. Spectra were obtained in the 50-500 cm-1 wavenumber range at 296 K and 9.91, 20, 50 and 100 mbar with a resolution of 0.00074, 0.00134, 0.0034 and 0.0067 cm-1 (FWHM of the sinc function), respectively. The rotational clusters are fully resolved and the good signal-to-noise ratio has enabled precise measurements of transition intensities (92 cold band lines and 96 Dyad-Dyad hot band lines, with normal abundance intensities in the range 2.10-26 to 1.10-24 cm-1/(molecule.cm-2)), yielding an accurate determination of the dipole moment derivatives. Such results should allow a better determination of CH4 concentration in planetary objects.

We measured the temperature dependence of the infrared absorption spectrum of 1-butyl-1 methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14-TFSI) between 160 and 330 K, through all the phase transitions presented by this compound. The comparison of the experimental spectra with the calculated vibration modes of different conformers of the ions composing the ionic liquid allowed to detect the presence of both conformers of TFSI in the liquid, supercooled, and glass phases, while only the trans-conformer is retained in both solid phases. When the ionic liquid swells a polyvinylidenefluoride (PVdF) electrospun membrane, the cis-rotamer is detected in all phases, since the interaction between the polymer and the ionic liquid inhibits the complete transformation of TFSI into the trans-conformer in the solid phases. Computational results confirm that in the presence of a PVdF chain, cis-TFSI becomes the lowest energy conformer. Therefore, the interaction with the polymer alters the physical properties of the ionic liquid. (C) 2015 AIP Publishing LLC.

This study reviews the various mechanisms exploited to produce infrared synchrotron radiation (IRSR). It shows that at long wavelengths (long when compared to the critical wavelength of the bending magnet in an electron storage ring), the radiation emitted from a bending magnet edge can be brighter than standard synchrotron radiation. For this purpose, we will discuss the various IRSR sources, namely the bending magnets, the wigglers, the undulator and the bending magnet edges. We will then briefly review a high-resolution study of isolated molecules in the far infrared, the detection of a very narrow Drude term in a high- T c superconductor, a description of ultra-high pressure experiments, an investigation of water encapsulated in non-ionic reverse micelles, and finally, a brief review of spatially resolved studies.

We report on the first simultaneous observations of both electronic and structural temperature-induced insulator-to-metal transition (IMT) in VO2 ultrathin films, made possible by the use of broad range transmission infrared spectroscopy. Thanks to these techniques, the infrared phonon structures, as well as the appearance of the free carrier signature, were resolved for the first time. The temperature-resolved spectra allowed the determination of the temperature hysteresis for both the structural (monoclinic-to-rutile) and electronic (insulator-to-metallic) transitions. The combination of these new observations and DFT simulations for the monoclinic structure allows us to verify the direct transition from monoclinic (M1) to rutile and exclude an intermediate structural monoclinic form (M2). The delay in structural modification compared to the primer electronic transition (325 K compared to 304 K) supports the role of free charges as the transition driving force. The shape of the free charge hysteresis suggests that the primer electronic transition occurs first at 304 K, followed by both its propagation to the heart of the layer and the structural transition when T increases. This study outlines further the potential of VO2 ultrathin films integrated on silicon for optoelectronics and microelectronics. (Some figures may appear in colour only in the online journal)