EXAFS Studies of Zn1-xMnxS Ternary Compounds

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Response to W. K. Warburton's Comments on Treatment of EXAFS data taken in the fluorescence mode in non-linear conditions by G. Ciatto et al. (2004). J. Synchrotron Rad. 11, 278–283

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New opportunities in trace elements structural characterization: high-energy X-ray absorption near-edge structure spectroscopy

Garnets in lower crustal mafic and ultramafic rocks usually contain rare-earth elements (REE) in trace concentrations. Direct characterization of REE at trace levels in natural garnets is not available in the literature because of the difficulty of obtaining structural information by means of conventional diffraction methods. Here, the characterization of Nd at trace levels (176-1029 p.p.m.) in a set of natural garnets performed by means of Nd K-edge X-ray absorption near-edge structure spectroscopy is presented, showing the capability of high-energy XANES for REE in trace structural determinations

Ultrafast Charge Carrier Dynamics in Vanadium-Modified TiO2 Thin Films and Its Relation to Their Photoelectrocatalytic Efficiency for Water Splitting

Light absorption and charge transport in oxide semiconductors can be tuned by the introduction, during deposition, of a small quantity of foreign elements, leading to the improvement of the photoelectrocatalytic performance. In this work, both unmodified and vanadium-modified TiO2 thin films deposited by radio-frequency magnetron sputtering are investigated as photoanodes for photoelectrochemical water splitting. Following a structural characterization by X-ray diffraction, atomic force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, photoelectrocatalysis is discussed based on ultrafast transient absorbance spectroscopy measurements. In particular, three different pump wavelengths from UV to the visible range are used (300, 390, and 530 nm) in order to cover the relevant photoactive spectral range of modified TiO2. Incident photon-to-current conversion efficiency spectra show that incorporation of vanadium in TiO2 extends water splitting in the visible range up to approximate to 530 nm, a significant improvement compared to unmodified TiO2 that is active only in the UV range less than or similar to 390 nm. However, transient absorbance spectroscopy clearly reveals that vanadium accelerates electron-hole recombination upon UV irradiation, resulting in a lower photon-to-current conversion efficiency in the UV spectral range with respect to unmodified TiO2. The new photoelectrocatalytic activity in the visible range is attributed to a V-induced introduction of intragap levels at approximate to 2.2 eV below the bottom of the conduction band. This is confirmed by long-living transient signals due to electrons photoexcited into the conduction band after visible light (530 nm) pulses. The remaining holes migrate to the semiconductor-electrolyte interface where they are captured by long-lived traps and eventually promote water oxidation under visible light

Anomalous wide-angle X-ray scattering apparatus on the GILDA beamline at the ESRF.

The experimental apparatus for anomalous wide-angle X-ray scattering (AWAXS) on the GILDA beamline at the ESRF is described. The main features are the high beam stability and reproducibility which allow anomalous scattering effects to be resolved also on dilute elements, the large spectral range which allows AWAXS experiments at the K edges of heavy elements, and the use of a high-efficiency detection system. The apparatus has been tested in extreme conditions by performing AWAXS experiments at the Eu K edge in Eu-doped Sr metaphosphate glasses

Long-lived nonthermal electron distribution in aluminum excited by femtosecond extreme ultraviolet radiation

We report a time-resolved study of the relaxation dynamics of Al films excited by ultrashort intense free-electron laser (FEL) extreme ultraviolet pulses. The system response was measured through a pump-probe detection scheme, in which an intense FEL pulse tuned around the Al L2,3 edge (72.5 eV) acted as the pump, while a time-delayed ultrafast pulse probed the near-infrared (NIR) reflectivity of the Al film. Remarkably, following the intense FEL excitation, the reflectivity of the film exhibited no detectable variation for hundreds of femtoseconds. Following this latency time, sizable reflectivity changes were observed. Exploiting recent theoretical calculations of the EUV-excited electron dynamics [N. Medvedev et al., Phys. Rev. Lett. 107, 165003 (2011)], the delayed NIR-reflectivity evolution is interpreted invoking the formation of very-long-living nonthermal hot electron distributions in Al after exposure to EUV pulses. Our data represent the first evidence in the time domain of such an intriguing behavior