Operando XPS: A Novel Approach for Probing the Lithium/Electrolyte Interphase Dynamic Evolution.

The coupling protocols combining photoemission spectroscopy and other characterization methods such as electrochemical, electrical, optical, thermal, or magnetic paved the way to considerable progress in the field of materials science. Access to complementary data on the same object is relevant, but in the vast majority of cases, it is carried out sequentially and separately. This raises the complex question of the equivalence of the analyzed surfaces subjected to these different characterizations. In the frame of lithium ion battery technology (LIB), several techniques have been developed to follow in operando condition the reactivity of electro-active materials toward liquid or solid electrolytes. Besides the knowledge of the redox processes obtained using operando protocols, especially at the interfaces, some limitations associated with material sensitivity and/or the characterization techniques are still a breakdown to widen our understanding of the origin of the LIB performance degradation processes. Herein, we propose a new design of an operando cell adapted to perform X-ray photoemission spectroscopy (XPS) at the interface between electrode and electrolyte under electrochemical solicitations. To illustrate its performance, the crucial issues associated with the lithium metal interface have been scrutinized using Li/Li symmetrical cells and two types of ionic liquids, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C1C6ImTFSI) and 1-hexyl-3-methylimidazolium bis(fluorosulfonyl)imide (C1C6ImFSI) laden with LiTFSI salt. Our original setup allowed us to follow-up the lithium surface reactivity toward these ionic liquid based electrolytes in open circuit voltage condition and under polarization. Beside the gain of time and the matter saving, we highlighted and optimized the blocking issues to perform accurate OXPS measurement for probing the evolution of the chemical structure and the surface potential change at the interface lithium/electrolyte in dynamic mode.

Method to determine radiative and non-radiative defects applied to AgInS2-ZnS luminescent nanocrystals.

The systematic measurement of the photoluminescence quantum yield and the recombination lifetime of a given phosphor allows for the quantification of both radiative and non-radiative recombination rates. This analysis therefore separates the two types of phenomena influencing the quantum efficiency of the phosphor. When associated with other materials characterizations, this powerful tool allows for the determination of the relationship between the structural properties and the efficiency of the photoluminescence process. This article presents this method and its direct application to emerging luminescent quaternary semiconductor nanocrystals. First, the direct effect of disorder on non-radiative recombination rate is demonstrated. Then, strong evidence concerning the nature of the donor and acceptor defects involved in the photoluminescence process of these materials are obtained using XPS.

New Interpretation of X-ray Photoelectron Spectroscopy of Imidazolium Ionic Liquid Electrolytes Based on Ionic Transport Analyses.

We reported a new perspective on the correlation between the electronic structure of an ionic liquid (IL)-based electrolyte probed by X-ray photoelectron spectroscopy and the transport properties analyzed by impedance spectroscopy. We highlighted the core level chemical shifts of 1-hexyl-3-methylimidazolium (bis(trifluoromethanesulfonyl)imide) (C1C6ImTFSI), 1-hexyl-3-methylimidazolium bis(fluorosulfonyl)imide (C1C6ImFSI), and 1-hexyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide (C1C1C6ImTFSI) laden with LiTFSI salt and vinylene carbonate (VC) or fluoroethylene carbonate (FEC) with regard to the transport properties of cations and anions. We pointed out based on detailed binding energy shift analyses a clear effect of the anion on the local organization of Li+ ions. The significant peak shift in the case of C1C6ImTFSI laden with LiTFSI corroborates the formation of [Li(TFSI)2]- complexes. On the contrary, the lower amplitude of the binding energy shift of C1C6ImFSI for both anion- and cation-related peaks indicates that the electronic distribution around the cation and the anion is not affected when the LiTFSI salt is added, which plays a strong role in the ion dynamics (lower viscosity) of the electrolyte. The X-ray photoelectron spectroscopy (XPS) result supports the preponderant role of imidazolium ionic liquid based on FSI anion to form an electrolyte less prone to form ionic complexes. The methylation of the imidazolium cation contributes to the reduction of the interaction between the C1C1C6Im cation and TFSI anion, while additives VC and FEC contribute to the change of the alkyl configuration in C1C6Im cation, leading to the modification of the macroscopic properties of the ILs.

Electrochemical Impedance Spectroscopy and X-ray Photoelectron Spectroscopy Study of Lithium Metal Surface Aging in Imidazolium-Based Ionic Liquid Electrolytes Performed at Open-Circuit Voltage.

Lithium reactivity toward an electrolytic media and dendrite growth phenomenon constitutes the main drawback for its use as an anode material for the lithium battery technology. Ionic liquids (ILs) were pointed out as promising electrolyte solvent candidates to prevent thermal runaway in a lithium battery system. However, the reactivity of lithium toward such a kind of an electrolyte is still under debate. In this study, the interaction between lithium metal and imidazolium-based ILs, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C1C6ImTFSI) and 1-hexyl-3-methylimidazolium bis(fluorosulfonyl)imide (C1C6ImFSI), has been investigated based on the nondestructive methodology coupling electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) in coin cells aged several days at open-circuit voltage. The main components detected by XPS in the bulk separator and at the surface of the lithium metal are the byproducts of cation and anion degradation. Similarities and differences were noticed depending on the anion nature of bis(trifluoromethylsulfonyl)imide versus bis(fluorosulfonyl)imide. The role of lithium salt addition (LiTFSI) was also pointed, giving rise to the stability improvement of the electrolytic solution toward the lithium anode. A direct correlation between the resistance of the bulk electrolyte and of the interface electrolyte/lithium and chemical composition changes were established based on a detailed EIS and XPS combined study.

Thermal behaviour of ytterbium-doped fluorite crystals under high power pumping.

We report an in situ thermal study of Yb-doped fluorite crystals Yb:CaF(2) and Yb:SrF(2) under high power pumping, with or without laser operation. The experiment combines simultaneously thermography and measurement of the thermal aberrations. This setup allows us to measure temperature gradients, thermal lens, and absorption coefficients. From these measurements, we evaluate the thermal conductivity, fractional thermal load, and thermo-optic coefficient. Great differences are observed between the lasing and non lasing regimes. Our measured thermal lenses are greater than what are expected from the thermo-optic parameters found in previous work. Based on this thermal study, we design a laser cavity operating with large output power and TEM(00), leading to better performances for Yb:CaF(2) than Yb:SrF(2).

Structural steady states and relaxation oscillations in a two-phase fluid under shear flow: experiments and phenomenological model.

By means of several rheophysics techniques, we report on an extensive study of the couplings between flow and microstructures in a two-phase fluid made of lamellar (L(alpha)) and sponge (L(3)) phases. Depending on the nature of the imposed dynamical parameter (stress or shear rate) and on the experimental conditions (brine salinity or temperature), we observe several different structural steady states consisting of either multilamellar droplets (with or without a long range order) or elongated (L(3)) phase domains. Two different astonishing phenomena, shear-induced phase inversion and relaxation oscillations, are observed. We show that (i) phase inversion is related to a shear-induced topological change between monodisperse multilamellar droplets and elongated structures and (ii) droplet size relaxation oscillations result from a shear-induced change of the surface tension between both coexisting (L(alpha)) and (L(3)) phases. To explain these relaxation oscillations, we present a phenomenological model and compare its numerical predictions to our experimental results.

Ochratoxin A in human plasma in Morocco: a preliminary survey.

Available epidemiological information seems to indicate that Balkan endemic nephropathy is associated with consumption patterns involving foodstuffs contaminated with ochratoxin A (OTA) and with a higher frequency of OTA-positive blood samples. The aim of this preliminary study was to assess OTA concentrations in human plasma in Morocco. Therefore, samples from 309 healthy volunteers (213 males, 96 females) were analysed. The analyses revealed that 60% of the human plasma sampled was positive for OTA (61.5% in the male and 56% in the female population), and an average concentration of 0.29 ng/mL (0.31 ng/mL in males, 0.26 ng/mL in females). The highest concentration found was 6.59 ng/mL. The results suggest that the Moroccan population is exposed to OTA, even though the OTA plasma levels are lower than that reported in some North African countries.

Mode-locked operation of a diode-pumped femtosecond Yb:SrF2 laser.

Femtosecond mode-locked operation is demonstrated for the first time, to our knowledge, with a Yb:SrF(2) crystal. The shortest pulse duration is 143 fs for an average power of 450 mW. The highest average power is 620 mW for a pulse duration of 173 fs. Since Yb:SrF(2) corresponds to the longest-lifetime Yb-doped crystal with which the mode-locking operation has been achieved, a detailed analysis is carried out to characterize the quality of the solitonlike regime.

Diode-pumped 99 fs Yb:CaF2 oscillator.

We demonstrate the generation of 99 fs pulses by a mode-locked laser oscillator built around a Yb:CaF(2) crystal. An average power of 380 mW for a 13 nm bandwidth spectrum centered at 1053 nm is obtained. The short-pulse operation is achieved thanks to a saturable absorber mirror and is stabilized by the Kerr lens effect. We investigated the limits of the stabilization process and observed a regime slowly oscillating between mode locking and Q switching.

The conformation of linear gramicidin is sequence dependent. A monolayer and infrared study.

A comparative monolayer and infrared study of analogues of gramicidin A containing either tyrosines or naphthylalanines instead of tryptophans indicates that the nature of the aromatic residues influences the favoured conformation of the peptides. Polar residues favour the single stranded IIDL helix while non polar residues favour the double stranded helix. For partly tryptophan to naphthylalanine substituted analogues the positions of the substitutions orientate the favored conformation. The nature of these substitutions may also modify the peptide-lipid interactions.

Single channel and monolayer studies of acylated gramicidin A: influence of the length of the alkyl group.

Three different gramicidin A analogues bearing acyl chains of various length on the ethanolamine moiety have been studied by investigating their single channel behaviour and their monolayer properties. It is shown that the single channel conductance does not depend on the substitution of the ethanolamine OH group and that the channel lifetime is roughly proportional to the length of the alkyl chain. The monolayer study indicates that acylation of gramicidin A produces compounds which have medium-dependent conformations. These acylated compounds are miscible with lipids, while GA is not, and the surface potential is not modified by the esterification of the alcohol group.