Bismuth-oxide nanoparticles: study in a beam and as deposited

Bi2O3 is a promising material for solid-oxide fuel cells (SOFC) due to the high ionic conductivity of some phases. The largest value is reached for its δ-phase, but it is normally stable at temperatures too high for SOFC operation, while nanostructured oxide is believed to have more suitable stabilization temperature. However, to manufacture such a material with a controlled chemical composition is a challenging task. In this work, we investigated the fabrication of nanostructured Bi2O3 films formed by deposition of free Bi-oxide nanoparticles created in situ. The particle-production method was based on reactive sputtering and vapour aggregation. Depending on the fabrication conditions, the nanoparticles contained either a combination of Bi-metal and Bi-oxide, or only Bi-oxide. Prior to deposition, the free particles were probed in the beam - by synchrotron-based photoelectron spectroscopy (PES), which allowed assessing their composition "on the-fly". The nanoparticle films obtained after deposition were studied by PES, scanning electron microscopy, transmission electron microscopy, and electron diffraction. The films' chemical composition, grain dimensions, and crystal structure were probed. Our analysis suggests that our method produced Bi-oxide films in more than one polymorph of Bi2O3.

Radiation damage by extensive local water ionization from two-step electron-transfer-mediated decay of solvated ions

Biomolecular radiation damage is largely mediated by radicals and low-energy electrons formed by water ionization rather than by direct ionization of biomolecules. It was speculated that such an extensive, localized water ionization can be caused by ultrafast processes following excitation by core-level ionization of hydrated metal ions. In this model, ions relax via a cascade of local Auger-Meitner and, importantly, non-local charge- and energy-transfer processes involving the water environment. Here, we experimentally and theoretically show that, for solvated paradigmatic intermediate-mass Al3+ ions, electronic relaxation involves two sequential solute-solvent electron transfer-mediated decay processes. The electron transfer-mediated decay steps correspond to sequential relaxation from Al5+ to Al3+ accompanied by formation of four ionized water molecules and two low-energy electrons. Such charge multiplication and the generated highly reactive species are expected to initiate cascades of radical reactions.

Time-of-flight photoelectron momentum microscopy with 80-500 MHz photon sources: electron-optical pulse picker or bandpass pre-filter

The small time gaps of synchrotron radiation in conventional multi-bunch mode (100-500 MHz) or laser-based sources with high pulse rate (∼80 MHz) are prohibitive for time-of-flight (ToF) based photoelectron spectroscopy. Detectors with time resolution in the 100 ps range yield only 20-100 resolved time slices within the small time gap. Here we present two techniques of implementing efficient ToF recording at sources with high repetition rate. A fast electron-optical beam blanking unit with GHz bandwidth, integrated in a photoelectron momentum microscope, allows electron-optical `pulse-picking' with any desired repetition period. Aberration-free momentum distributions have been recorded at reduced pulse periods of 5 MHz (at MAX II) and 1.25 MHz (at BESSY II). The approach is compared with two alternative solutions: a bandpass pre-filter (here a hemispherical analyzer) or a parasitic four-bunch island-orbit pulse train, coexisting with the multi-bunch pattern on the main orbit. Chopping in the time domain or bandpass pre-selection in the energy domain can both enable efficient ToF spectroscopy and photoelectron momentum microscopy at 100-500 MHz synchrotrons, highly repetitive lasers or cavity-enhanced high-harmonic sources. The high photon flux of a UV-laser (80 MHz, <1 meV bandwidth) facilitates momentum microscopy with an energy resolution of 4.2 meV and an analyzed region-of-interest (ROI) down to <800 nm. In this novel approach to `sub-µm-ARPES' the ROI is defined by a small field aperture in an intermediate Gaussian image, regardless of the size of the photon spot.

Note: Soft X-ray transmission polarizer based on ferromagnetic thin films

A transmission polarizer for producing elliptically polarized soft X-ray radiation from linearly polarized light is presented. The setup is intended for use at synchrotron and free-electron laser beamlines that do not directly offer circularly polarized light for, e.g., X-ray magnetic circular dichroism (XMCD) measurements or holographic imaging. Here, we investigate the degree of ellipticity upon transmission of linearly polarized radiation through a cobalt thin film. The experiment was performed at a photon energy resonant to the Co L₃-edge, i.e., 778 eV, and the polarization of the transmitted radiation was determined using a polarization analyzer that measures the directional dependence of photo electrons emitted from a gas target. Elliptically polarized radiation can be created at any absorption edge showing the XMCD effect by using the respective magnetic element.

Ultrafast Charge Transfer Processes Accompanying KLL Auger Decay in Aqueous KCl Solution

X-ray photoelectron and KLL Auger spectra were measured for the K^{+} and Cl^{-} ions in aqueous KCl solution. While the XPS spectra of these ions have similar structures, both exhibiting only weak satellites near the main line, the Auger spectra differ dramatically. Contrary to the chloride case, a very strong extra peak was found in the Auger spectrum of K^{+} at the low kinetic energy side of the ^{1}D state. Using the equivalent core model and ab initio calculations this spectral feature was assigned to electron transfer processes from solvent water molecules to the solvated cation. The observed charge transfer processes are suggested to play an important role in charge redistribution following single and multiple core-hole creation in atoms and molecules placed into environment.

Alcohols at the aqueous surface: chain length and isomer effects

Alcohol isomers at the water–vapor interface were studied to determine free energies of adsorption, surface concentrations and enrichment factors.

Surface behavior of amphiphiles in aqueous solution: a comparison between different pentanol isomers

Molecular-level understanding of concentration-dependent changes in the surface structure of different amphiphilic isomers at the water–vapor interface was gained by molecular dynamics (MD) simulation and X-ray photoelectron spectroscopy (XPS).

Donor–anion interactions at the charge localization and charge ordering transitions of (TMTTF)2AsF6 probed by NEXAFS

Detection of the charge localization and charge ordering transitions of (TMTTF)₂AsF₆ at T_ρ ≈ 230 K and T_CO ≈ 102 K, respectively.

K-shell x-ray spectroscopy of atomic nitrogen

Absolute K-shell photoionization cross sections for atomic nitrogen have been obtained from both experiment and state-of-the-art theoretical techniques. Because of the difficulty of creating a target of neutral atomic nitrogen, no high-resolution K-edge spectroscopy measurements have been reported for this important atom. Interplay between theory and experiment enabled identification and characterization of the strong 1s → np resonance features throughout the threshold region. An experimental value of 409.64±0.02  eV was determined for the K-shell binding energy.