We show that dissociative oxygen adsorption on Ag͑001͒ induces below room temperature a missing row 2ͱ2ϫͱ2 reconstruction of the substrate. As demonstrated by the analysis of the photoelectron diffraction patterns, the oxygen atoms sit thereby in a c(2ϫ2) arrangement in the previous fourfold hollow sites nearly coplanar with the Ag atoms, while rows of substrate atoms are removed along the ͓100͔ directions. Annealing the crystal above 350 K restores the p(1ϫ1) symmetry and the oxygen moves to 0.6 Å above the fourfold hollow site. It becomes then more oxidic in nature, as demonstrated by the shift of the O 1s level from 530.3 eV to 528.3 eV. The phase transition affects also the O 2s and O 2p levels as well as the surface component of Ag 3d 5/2 . The vibrational frequency of the oxygen adatoms against the surface decreases at the phase transition, in accord with the larger adsorption distance. The higher temperature phase is active towards CO and C 2 H 4 oxidation, while the low-temperature phase is not. When cooling the sample below room temperature the reconstructed phase is restored. The time constant of this process as well as the chemical reactivity of the high-temperature phase are weakly reproducible since they depend on the previous history, i.e., presumably on the subsurface oxygen content of the sample.

We present thick, uniform and rather flat melanin films obtained using spray deposition. The morphology of the films was investigated using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Temperature-dependent electrical resistance of melanin thin films evidenced a semiconductor-like character and a hysteretic behavior linked to an irreversible process of water molecule desorption from the melanin film. X-ray Photoelectron Spectroscopy (XPS) was carried out to analyze the role of the functional groups in the primary and secondary structure of the macromolecule, showing that the contribution of the 5,6-dihydroxyindole-2-carboxylic acid (DHICA) subunit to the molecule is about 35%. Comparison of the optical absorption of the thick (800nm) and thin (80nm) films showed a spectral change when the thickness increases. From in vacuum photoconductivity (PC) measured at controlled temperatures, we suggest that the melanin films exhibit a possible charge transport mechanism by means of delocalized pi states along the stacked planar secondary structure.

Advanced metal oxide electrodes in Li-ion batteries usually show reversible capacities exceeding the theoretically expected ones. Despite many studies and tentative interpretations, the origin of this extra-capacity is not assessed yet. Lithium storage can be increased through different chemical processes developing in the electrodes during charging cycles. The solid electrolyte interface (SEI), formed already during the first lithium uptake, is usually considered to be a passivation layer preventing the oxidation of the electrodes while not participating in the lithium storage process. In this work, we combine high resolution soft X-ray absorption spectroscopy with tunable probing depth and photoemission spectroscopy to obtain profiles of the surface evolution of a well-known prototype conversion-alloying type mixed metal oxide (carbon coated ZnFeO) electrode. We show that a partially reversible layer of alkyl lithium carbonates is formed (∼5-7 nm) at the SEI surface when reaching higher Li storage levels. This layer acts as a Li reservoir and seems to give a significant contribution to the extra-capacity of the electrodes. This result further extends the role of the SEI layer in the functionality of Li-ion batteries.

found to be able to exchange Li + and e -both by conversion and alloying processes. As a consequence Fe, LiZn, Li 2 O are formed upon lithiation, which are fi nely dispersed into a carbonaceous matrix, [ 7 ] according to a reversible reaction involving nine lithium ions per formula unit of ZFO and resulting in a capacity of ≈1000 mAh g −1 . [ 7 ] While the lithiation kinetics have already been probed by electrochemical impedance spectroscopy (EIS) and X-ray diffraction (XRD) analysis, [ 5,7 ] very little is known about the evolution of passivation layer properties on ZFO-C.The aim of this work is to study the evolution of the SEI in this innovative anode material at selected charging steps by exploiting the surface sensitivity [10][11][12] of the soft X-ray absorption spectroscopy (XAS). This technique requires synchrotron radiation and was never used before for such a purpose, although it appears to be very suitable for a detailed depth profi ling of the SEI of advanced electrodes. In fact, XAS experiments in the 50-1000 eV photon energy range can be typically performed using both total electron (TEY) and total fl uorescence (TFY) yield techniques for which effective probing depths are around 2-10 nm and 70-200 nm, respectively. In this study, ex situ TEY and TFY X-ray absorption experiments have been conceived and realized to study the modifi cation of the signals related to the various atomic species in ZFO-C electrodes selected at different states of charge during the fi rst Li insertion process. XAS measurements have been preceded and corroborated by a complete electrochemical characterization including galvanostatic intermittent titration technique (GITT) and EIS, with the aim of correlating each XAS experiment with half-cell open-circuit potential (OCV) and charge, and to crosscheck the SEI evolution with the polarization of the electrodes.The samples for the experiments were prepared using carbon-coated ZFO nanoparticles (ZFO-C), obtained [ 7 ] by dispersing 1 g of ZFO powder (<100 nm, Aldrich Chemistry) in 1.5 mL of an aqueous carbon precursor solution of sucrose (Acros Organics), followed by an annealing step under inert gas atmosphere. The weight ratio was 1:0.75 for ZFO:Suc. The obtained dispersion was homogenized by means of a planetary ball mill (Vario-Planetary Mill Pulverisette 4, FRITSCH, 2× 45 min at 400/−800 rpm with 10 min rest in between). Subsequently, the dispersion was dried at 70 °C under ambient atmosphere. After grinding, the resulting composite powder was annealed in a tubular furnace (R50/250/12, Nabertherm) at 450 °C for 4 h under a constant argon gas stream. The heating rate was set to 3 °C min −1 . The material was investigated by SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy) revealing that it is formed by nanoparticles of average linear dimensions of about 50 nm, with formation of some ZnFe 2 O 4 Li-ion batteries (LIBs) represent a reliable, affordable, and safe energy storage technology for use in portable application. However, current LIB active ...

FERMI@Elettra is a free electron-laser (FEL)-based user facility that, after two years of commissioning, started preliminary users' dedicated runs in 2011. At variance with other FEL user facilities, FERMI@Elettra has been designed to deliver improved spectral stability and longitudinal coherence. The adopted scheme, which uses an external laser to initiate the FEL process, has been demonstrated to be capable of generating FEL pulses close to the Fourier transform limit. We report on the first instance of FEL wavelength tuning, both in a narrow and in a large spectral range (fine-and coarse-tuning). We also report on two different experiments that have been performed exploiting such FEL tuning. We used fine-tuning to scan across the 1s-4p resonance in He atoms, at ≈23.74 eV (52.2 nm), detecting both UV-visible fluorescence (4p-2s, 400 nm) and EUV fluorescence (4p-1s, 52.2 nm). We used coarse-tuning to scan the M 4,5 absorption edge of Ge (∼29.5 eV) in the wavelength region 30-60 nm, measured in transmission geometry with a thermopile positioned on the rear side of a Ge thin foil.

We examine the formation of the solid electrolyte interface (SEI) on anodes made of carbon encapsulated zinc ferrite (ZnFe 2 O 4 ) nanoparticles (50 nm ZFO-C) as a standard metal oxide electrode prototype. The SEI formation and phase evolution are studied by two soft X-ray absorption techniques with different probing depths in the 10−100 nm range and by surface-sensitive X-ray photoemission spectroscopy at several specific capacities of the ZFO-C anodes. These techniques are shown to be able to provide information about the nature and extension of the individual chemical species within the SEI with a typical spatial resolution of 1−5 nm. A peculiar footprint of the interphase formations is obtained by comparing the chemical history of the reactive element sites in the anodes. The progressive development of the SEI in the first cycle and the variety of compositional transformations prior to stabilization are elucidated. Formation of a reversible alkyl carbonate layer, with maximum thickness of 7 nm, is detected at the SEI topmost region. On the basis of these results, we have obtained a map of suitable spatial resolution of the evolution of the different components of the interface layer.

The structural and electronic properties of Mn x Ge 1−x alloys ͑x ഛ 0.15͒ fabricated by ion implantation are investigated by means of x-ray diffraction and synchrotron radiation photoemission spectroscopy. The diffraction patterns point to the presence of ferromagnetic Mn 5 Ge 3 nanoparticles; however, valence band spectra, interpreted by means of accurate ab initio calculations including Hubbard-like correlations, show clear fingerprints of an effective substitutional Mn dilution in the Ge semiconducting host.

The capability to monitor finely the physical properties of eumelanin, an important class of biopolymers, involved in melanoma cancer pathologies, whose function and intrinsic disorder still collects the interest of many investigators, was achieved by means of electrospray deposition (ESD). By alleviating the problem of the solubility of melanin through the realization of high-quality films it was possible to spread light on the unknown biopolymer supramolecular organization. In fact, on the basis of scanning probe microscopies, electron spectroscopies, and transport properties, it was possible to delineate peculiar features of the melanin organization varying from heteropolymeric to oligomeric in character and eventually turning in a cross-linked secondary molecular structure.