Does Alumina Coating Alter the Solid Permeable Interphase Dynamics in LiMn2O4 Cathodes?

It is well known that the Al2O3 coating of the LiMn2O4 cathodes leads to improvement of the performance of these electrodes. However, the effect of the coating on the fundamental processes occurring on the interface with the active material which results in the formation of the solid permeable interphase is yet to be investigated. These effects should be more pronounced in the first cycle when a dynamic interaction of the active material at high voltage with the electrolyte and binder leads to the formation of this passivation layer. Here, we present a detailed investigation of the solid permeable interphase formation in alumina-coated and uncoated LiMn2O4 electrodes using X-ray absorption spectroscopy and analysis on the electrodes at the predesigned charging/ discharging states. We demonstrate that the alumina coating leads to modification of the solid permeable layer and its dynamics. We also discuss the possible influences of interface modifications via coating on the battery performance

How the Environment Encourages the Natural Formation of Hydrated V2O5

Herein, we report the microscopic and spectroscopic signatures of the hydrated V2O5 phase, prepared from the alpha-V2O5 powder, which was kept in deionized water inside an airtight glass container for approximately 2.5 years. The experimental results show an evolution of the V4+ component in V 2p(3/2) core energy level spectra, and a peak corresponding to sigma-OH- bond appeared in the valence band spectra in the hydrated V2O5 powder sample due to the water intercalation. Vanadium metal oxide particles were found to be self-nucleated into micro/nanorods after a long period of exposure to an extremely humid environment. The distinct features in the spectra obtained with high-resolution transmission electron microscopy, micro-Raman scattering, and X-ray photoelectron spectroscopy confirmed the presence of structural water molecules for the first time in the long-aged naturally hydrated V2O5 phase

Angular correlation between photoelectrons and Auger electrons within scattering theory

International audienceIn this paper we present a single-particle scattering approach for the angular correlation between a photoelectron and the subsequent Auger electron from atomic targets. This method is proposed as an alternative approach with respect to the usual density matrix formalism, since it is more convenient for extension to the solid state case. Such an extension is required by the great progress made in the field of coincidence spectroscopy in condensed matter systems. We derived a tensor expression for the cross section and an equivalent expression in terms of convenient angular functions has been treated for the case of linearly polarized light. Numerical calculations are performed for the L3M2,3M2,3 transition in argon, in the single configuration Dirac-Fock scheme. Results are compared with experimental data for different final angular momentum states of the doubly charged ion and for different kinematical conditions

Physico-Chemical Characterization of Keratin from Wool and Chicken Feathers Extracted Using Refined Chemical Methods

In this work, the characteristic structure of keratin extracted from two different kinds of industrial waste, namely sheep wool and chicken feathers, using the sulfitolysis method to allow film deposition, has been investigated. The structural and microscopic properties have been studied by means of scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), and infrared (IR) spectroscopy. Following this, small-angle X-ray scattering (SAXS) analysis for intermediate filaments has been performed. The results indicate that the assembly character of the fiber can be obtained by using the most suitable extraction method, to respond to hydration, thermal, and redox agents. The amorphous part of the fiber and medium range structure is variously affected by the competition between polar bonds (reversible hydrogen bonds) and disulfide bonds (DB), the covalent irreversible ones, and has been investigated by using fine structural methods such as Raman and SAXS, which have depicted in detail the intermediate filaments of keratin from the two different animal origins. The preservation of the secondary structure of the protein obtained does offer a potential for further application of the waste-obtained keratin in polymer films and, possibly, biocomposites

Synchrotron radiation photoemission spectroscopy of the oxygen modified CrCl3 surface

We investigate the experimentally challenging CrCl3 surface by photon energy dependent photoemission (PE). The core and valence electrons after cleavage of a single crystal, either in a ultra-high vacuum (UHV) or in air, are studied by keeping the samples at 150 degrees C, aiming at confirming the atomic composition with respect to the expected bulk atomic structure. A common spectroscopic denominator revealed by data is the presence of a stable, but only partially ordered Cl-O-Cr surface. The electronic core levels (Cl 2p, Cr 2p and 3p), the latter ones of cumbersome component determination, allowed us to quantify the electron charge transfer to the Cr atom as a net result of this modification and the increased exchange interaction between metal and ligand atoms. In particular, the analysis of multiplet components by the CMT4XPS code evidenced the charge transfer to be favored, and similarly the reduced crystal field due to the established polarization field. Though it is often claimed that a significant amount of Cl and Cr atomic vacancies has to be included, such a possibility can be excluded on the basis of the sign and the importance of the shift in the binding energy of core level electrons. The present methodological approach can be of great impact to quantify the structure of ordered sub-oxide phases occurring in mono or bi-layer Cr trihalides

Broadband optical ultrafast reflectivity of Si, Ge and GaAs

Ultrafast optical reflectivity measurements of silicon, germanium, and gallium arsenide have been carried out using an advanced set-up providing intense subpicosecond pulses (35 fs FWHM, λ = 400 nm) as a pump and broadband 340–780 nm ultrafast pulses as a white supercontinuum probe. Measurements have been performed for selected pump fluence conditions below the damage thresholds, that were carefully characterized. The obtained fluence damage thresholds are 30, 20.8, 9.6 mJ/cm 2 for Si, Ge and GaAs respectively. Ultrafast reflectivity patterns show clear differences in the Si, Ge, and GaAs trends both for the wavelength and time dependences. Important changes were observed near the wavelength regions corresponding to the E1, E1+ Δ singularities in the joint density of states, so related to the peculiar band structure of the three systems. For Ge, ultrafast reflectivity spectra were also collected at low temperature (down to 80 K) showing a shift of the characteristic doublet peak around 2.23 eV and a reduction of the recovery times

Free electron laser-driven ultrafast rearrangement of the electronic structure in Ti

High-energy density extreme ultraviolet radiation delivered by the FERMI seeded free-electron laser has been used to create an exotic nonequilibrium state of matter in a titanium sample characterized by a highly excited electron subsystem at temperatures in excess of 10 eV and a cold solid-density ion lattice. The obtained transient state has been investigated through ultrafast absorption spectroscopy across the Ti M2,3-edge revealing a drastic rearrangement of the sample electronic structure around the Fermi level occurring on a time scale of about 100 fs

Tracking interfacial changes of graphene/Ge(110) during in-vacuum annealing

Graphene quality indicators obtained by Raman spectroscopy have been correlated to the structural changes of the graphene/Germanium interface as a function of in-vacuum thermal annealing. Specifically, it is found that graphene becomes markedly defected at 650 {\deg}C. By combining scanning tunneling microscopy, x-Ray Photoelectron Spectroscopy and Near Edge x-ray Absorption Fine Structure Spectroscopy, we conclude that these defects are due to the release of H_{2} gas trapped at the graphene/Germanium interface. The H_{2} gas was produced following the transition from the as-grown hydrogen-termination of the Ge(110) surface to the emergence of surface reconstructions in the substrate. Interestingly, a complete self-healing process is observed in graphene upon annealing to 800 {\deg}C. The subtle interplay revealed between the microscopic changes occurring at the graphene/Germanium interface and graphene's defect density is valuable for advancing graphene growth, controlled 2D-3D heterogeneous materials interfacing and integrated fabrication technology on semiconductors