[en] Luminescence spectral and kinetic characteristics of CsPbCl₃ nanocrystals, dispersed in perovskite-like CsSrCl₃ matrix, have been studied under excitation by synchrotron radiation in the UV-visible spectral region (4 to 20 eV). Various time components in the decay kinetics of CsPbCl₃ nanocrystals appear due to direct excitation of nanocrystals or reabsorption of the luminescence of other emitting centres. Shortening of the luminescence decay time of the CsPbCl₃ nanocrystals with respect to that observed for a CsPbCl₃ single crystal has been explained as evidence of quantum-size effect. (author)

[en] Time-of-flight photoemission electron microscopy was used to measure spatially resolved energy distribution curves of electrons emitted from Ag nanoparticle films with different mass thicknesses. Two-photon photoemission (2PPE) was induced by femtosecond laser pulse excitation with 3.1 eV photon energy and 200 fs pulse width. Regions of Ag nanoparticles with different average sizes and one region with a continuous 100 nm thick Ag film were deposited as a stepped wedge on a Si(1 1 1) substrate. Upon laser excitation the nanoparticle films exhibit a very high electron emission yield in the images, whereas the uncovered Si surface and the continuous Ag film are dark. The time-of-flight electron spectra obtained from the nanoparticle films are remarkably different from the spectra of the continuous film, well-known from literature. The nanoparticle spectra are up to a factor of 160 more intense than the spectrum of the continuous film. They reveal different widths, overall shape and a shift and broadening of the Fermi edge. The results are discussed in terms of Mie plasmon assisted two-photon photoemission of the nanoparticles

[en] We report high-resolution ARPES studies of the electronic structure of BaFe_2-xCo_xAs₂, Ba_1-xK_xFe₂As₂, FeTe(Se), and EuFe₂As₂. The results are compared with DFT band structure calculations. From photon energy dependent measurements, information on the band dispersion perpendicular to the Fe layers could be derived. with increasing Co doping in BaFe_2-xCo_xAs₂, the dimensionality increases and, due to the filling of the hole pockets, the nesting condition decreases. In the AFM phase of EuFe₂As₂ back-folded bands strongly hybridize with the non-folded bands leading to the opening of gaps around both high-symmetry points. This transforms the large Fermi surface of the PM phase into droplet Fermi surfaces in the AFM low-T phase.

No abstract available

[en] The PERCIVAL soft X-ray imager is being developed by DESY, RAL, Elettra, DLS, and PAL to address the challenges at high brilliance Light Sources such as new-generation Synchrotrons and Free Electron Lasers. Typical requirements for detector systems at these sources are high frame rates, large dynamic range, single-photon counting capability with low probability of false positives, high quantum efficiency, and (multi)-mega-pixel arrangements. PERCIVAL is a monolithic active pixel sensor, based on CMOS technology. It is designed for the soft X-ray regime and, therefore, it is post-processed in order to achieve high quantum efficiency in its primary energy range (250 eV to 1 keV) . This work will report on the latest experimental results on charge collection efficiency obtained for multiple back-side-illuminated test sensors during two campaigns, at the P04 beam-line at PETRA III, and the CiPo beam-line at Elettra, spanning most of the primary energy range as well as testing the performance for photon-energies below 250 eV . In addition, XPS surface analysis was used to cross-check the obtained results.

[en] We report an in situ thermochemical treatment that significantly increases the macroscopic electrical conductivity of insulating yttria-stabilized zirconia (YSZ) (001) single-crystalline substrates. We demonstrate the high-quality surface crystalline structure of the resulting “conductive” cYSZ (001) by low- and high-energy electron diffraction. Soft- and hard X-ray photoemission spectroscopy measurements reveal a sizable reduction of Zr cations to a metallic state and their homogeneous distribution within the cYSZ. We discuss the correlation between the microscopic chemical processes leading to the increased macroscopic metallicity. Finally, the heteroepitaxial growth of a functional magnetic oxide model system, ultrathin EuO on cYSZ (001), was demonstrated. cYSZ (001) thereby enables both high quality oxide heteroepitaxy and the advanced sample characterization by high electron-fluence characterization techniques

No abstract available

[en] Hard x-ray photoelectron diffraction (hXPD) patterns recorded with a momentum microscope with high k-resolution (0.025 Å⁻¹ equivalent to an angular resolution of 0.034° at 7 keV) reveal unprecedented rich fine structure. We have studied hXPD of the C 1s core level in the prototypical low-Z material Graphite at 20 photon energies between 2.8 and 7.3 keV. Sharp bright and dark lines shift with energy; regions of Kikuchi band crossings near zone axis exhibit a filigree structure which varies rapidly with energy. Calculations based on the Bloch wave approach to electron diffraction from lattice planes show excellent agreement with the experimental results throughout the entire energy range. The main Kikuchi bands in the [001] zone axis appear fixed on the momentum scale with a width of the corresponding reciprocal lattice vector, allowing to reconstruct the size of the projected Brillouin zone. The newly developed high-energy k-microscope allows full-field imaging of (k _x, k _y)-distributions in large k-fields (up to >22 Å⁻¹ dia.) and time-of-flight energy recording. (paper)

[en] V₂O₅ nanotubes synthesized via the sol-gel route has been studied by electron energy loss spectroscopy (EELS), x-ray absorption spectroscopy (XAS), and energy dispersive x-ray analysis, in order to understand the local structure of vanadium in the nanotubes. Contrary to our expectation, all the features of the XAS and EELS spectra of the V₂O₅ nanotubes are in line with that of bulk layered vanadium oxide revealing that vanadium is present in the 5⁺ oxidation state in the nanotubes. However, V₂O₅ nanotubes exhibit additional surface states in their electronic structure in comparison with bulk V₂O₅. A comparison of measured and calculated spectra allows us to distinguish single-wall from multiwall V₂O₅ nanotubes

[en] We present the chemical and structural optimization of ultrathin magnetic oxide EuO films on silicon. By applying a controlled in situ passivation of the Si(001) surface with SiO_x in the monolayer regime, metallic silicide contaminations at the interface can be effectively reduced down to a sub-monolayer coverage, as was carefully quantified by interface-sensitive hard x-ray photoemission spectroscopy. Heteroepitaxial growth of EuO on Si(001) is sustained for this ultrathin SiO_x-passivation, and bulk-near magnetic properties are observed for the 4 nm-thin EuO films. Our successful combination of chemically and structurally optimized EuO/Si(001) heterostructures by ultrathin in situ SiO_x passivation makes this system promising for an application as alternative spin functional tunnel contacts in spin-FETs.