X-ray fluorescence spectra of metals excited below threshold

X-ray scattering spectra of Cu and Ni metals have been measured using monochromatic synchrotron radiation tuned from far above to more than 10 eV below threshold. Energy conservation in the scattering process is found to be sufficient to explain the modulation of the spectral shape, neglecting momentum conservation and channel interference. At excitation energies close to and above threshold, the emission spectra map the occupied local partial density of states. For the sub-threshold excitations, the high-energy flank of the inelastic scattering exhibits a Raman-type linear dispersion, and an asymmetric low energy tail develops. For excitation far below threshold the emission spectra are proportional to a convolution of the occupied and unoccuppied local partial densities of states.Comment: 10 pages, 3 figures, http://link.aps.org/doi/10.1103/PhysRevB.68.04511

State dependent fluorescence yields through the core valence Coulomb exchange parameter

Total and partial fluorescence yield PFY L edge x ray absorption spectra differ from the transmission x ray absorption spectra XAS through state dependent fluorescence yield across the XAS. For 3d1 to 3d9 in octahedral symmetry we apply simulations of PFY and XAS and show how the atomic 2p3d Coulomb exchange parameter Gpd governs the differences in the L3 L2 L3 branching ratio between PFY and XAS. Gpd orders the XAS final states following Hund s rules creating a strong state dependent fluorescence decay strength variation across the XAS leading to the differences between PFY and XA

Crystal-field splitting in coadsorbate systems: c (2x2) CO/K/Ni (100)

It is demonstrated how the crystal field splitting (CFS) fine structure can be used to characterize a coadsor-bate system. We have applied K 2p x-ray absorption spectroscopy (XAS) to the c(2x2) CO/K/Ni(100) system. The CFS fine structure is shown to be sensitive to the the local atomic environment, the level of interaction, and the chemical state of the alkali atoms. From angle dependent XAS measurements, combined with x-ray photoelectron spectroscopy, a significant K-CO electrostatic adsorbate-adsorbate interaction is found, whereas the K-Ni interaction is substantially weaker. The present results provide evidence for a coad-sorbed overlayer best described in terms of the properties associated with an ionic (two-dimensional) crystal

Laser pump X ray probe experiments with electrons ejected from a Cu 111 target space charge acceleration

A comprehensive investigation of the emission characteristics for electrons induced by X rays of a few hundred eV at grazing incidence angles on an atomically clean Cu 111 sample during laser excitation is presented. Electron energy spectra due to intense infrared laser irradiation are investigated at the BESSY II slicing facility. Furthermore, the influence of the corresponding high degree of target excitation high peak current of photoemission on the properties of Auger and photoelectrons liberated by a probe X ray beam is investigated in time resolved pump and probe measurements. Strong electron energy shifts have been found and assigned to space charge acceleration. The variation of the shift with laser power and electron energy is investigated and discussed on the basis of experimental as well as new theoretical result

Towards time resolved core level photoelectron spectroscopy with femtosecond x-ray free-electron lasers

We have performed core level photoelectron spectroscopy on a W(110) single crystal with femtosecond XUV pulses from the free-electron laser at Hamburg (FLASH). We demonstrate experimentally and through theoretical modelling that for a suitable range of photon fluences per pulse, time-resolved photoemission experiments on solid surfaces are possible. Using FLASH pulses in combination with a synchronized optical laser, we have performed femtosecond time-resolved core-level photoelectron spectroscopy and observed sideband formation on the W 4f lines indicating a cross correlation between femtosecond optical and XUV pulses. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

Time and Angle Resolved Time of Flight Electron Spectroscopy for Functional Materials Science

Electron spectroscopy with the unprecedented transmission of angle resolved time of flight detection, in combination with pulsed X ray sources, brings new impetus to functional materials science. We showcase recent developments towards chemical sensitivity from electron spectroscopy for chemical analysis and structural information from photoelectron diffraction using the phase transition properties of 1T TaS2. Our development platform is the SurfaceDynamics instrument located at the Femtoslicing facility at BESSY II, where femtosecond and picosecond X ray pulses can be generated and extracted. The scientific potential is put into perspective to the current rapidly developing pulsed X ray source capabilities from Lasers and Free Electron Laser

Quantitative evaluation of transient valence orbital occupations in a 3d transition metal complex as seen from the metal and ligand perspective

It is demonstrated for the case of photo excited ferrocyanide how time resolved soft X ray absorption spectroscopy in transmission geometry at the ligand K edge and metal L3 edge provides quantitatively equivalent valence electronic structure information, where signatures of photo oxidation are assessed locally at the metal as well as the ligand. This allows for a direct and independent quantification of the number of photo oxidized molecules at two soft X ray absorption edges highlighting the sensitivity of X ray absorption spectroscopy to the valence orbital occupation of 3d transition metal complexes throughout the soft X ray rang

Ultrafast electronic processes in an insulator The Be and O sites in BeO

The short time dynamics of amorphous beryllium oxide a BeO has been investigated for electronic excitation ionization by fast incident electrons, as well as by Ar7 , Ar15 , Xe15 , and Xe31 ions at velocities of 6 10 the speed of light. Site specific Auger electron spectra induced by fast heavy ions are the central point of this investigation. Electron induced Auger spectra serve as a reference and electron energy loss EELS spectroscopy as well as resonant inelastic X ray scattering RIXS are invoked for quantitative understanding. For the heavy ion case, we observe strong variations in the corresponding spectral distributions of Be K and O K Auger lines. These are related to local changes of the electron density, of the electron temperature and even of the electronic band structure of BeO on a femtosecond time scale after the passage of highly charged heavy ions

X ray spectroscopy on the active ion in laser crystals

X-ray absorption and (resonant) emission spectroscopies combined measure the differences in crystal field parameters for the ground and core-excited states.</p