TY - GEN A1 - Eschenlohr, Andrea A1 - Battiato, Mario A1 - Maldonado, P. A1 - Pontius, N. A1 - Kachel, T. A1 - Holldack, K. A1 - Mitzner, Rolf A1 - Föhlisch, Alexander A1 - Oppeneer, P. M. A1 - Stamm, Christian T1 - Optical excitation of thin magnetic layers in multilayer structures Reply T2 - Nature materials Y1 - 2014 U6 - https://doi.org/10.1038/nmat3851 SN - 1476-1122 SN - 1476-4660 VL - 13 IS - 2 SP - 102 EP - 103 PB - Nature Publ. Group CY - London ER - TY - INPR A1 - Föhlisch, Alexander A1 - de Groot, F. M. F. A1 - Odelius, Michael A1 - Techert, Simone A1 - Wernet, P. T1 - Comment on "state-dependent electron delocalization dynamics at the solute-solvent interface: soft-x-ray absorption spectroscopy and lambda b initio calculations" T2 - Physical review letters Y1 - 2014 U6 - https://doi.org/10.1103/PhysRevLett.112.129302 SN - 0031-9007 SN - 1079-7114 VL - 112 IS - 12 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Holldack, Karsten A1 - Ovsyannikov, Ruslan A1 - Kuske, P. A1 - Mueller, R. A1 - Schaelicke, A. A1 - Scheer, M. A1 - Gorgoi, Mihaela A1 - Kuehn, D. A1 - Leitner, T. A1 - Svensson, S. A1 - Martensson, N. A1 - Föhlisch, Alexander T1 - Single bunch X-ray pulses on demand from a multi-bunch synchrotron radiation source JF - Nature Communications N2 - Synchrotron radiation facilities routinely operate in a multi-bunch regime, but applications relying on time-of-flight schemes require single bunch operation. Here we show that pulse picking by resonant excitation in a storage ring creates in addition to the multi-bunch operation a distinct and separable single bunch soft X-ray source. It has variable polarization, a photon flux of up to 10(7)-10(9) ph s(-1)/0.1%BW at purity values of 10(4)-10(2) and a repetition rate of 1.25 MHz. The quasi-resonant excitation of incoherent betatron oscillations of electrons allows horizontal pulse separation at variable (also circular) polarization accessible for both, regular 30 ps pulses and ultrashort pulses of 2-3 ps duration. Combined with a new generation of angularly resolving electron spectrometers this creates unique opportunities for time-resolved photoemission studies as confirmed by time-of-flight spectra. Our pulse picking scheme is particularly suited for surface physics at diffraction-limited light sources promising ultimate spectral resolution. Y1 - 2014 U6 - https://doi.org/10.1038/ncomms5010 SN - 2041-1723 VL - 5 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Miedema, Piter S. A1 - Wernet, Philippe A1 - Föhlisch, Alexander T1 - State-dependent fluorescence yields through the core-valence Coulomb exchange parameter JF - Physical review : A, Atomic, molecular, and optical physics N2 - 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 3d(1) to 3d(9) in octahedral symmetry we apply simulations of PFY and XAS and show how the atomic 2p3d Coulomb exchange parameter G(pd) governs the differences in the L-3/(L-2 + L-3) branching ratio between PFY and XAS. G(pd) 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 XAS. Y1 - 2014 U6 - https://doi.org/10.1103/PhysRevA.89.052507 SN - 1050-2947 SN - 1094-1622 VL - 89 IS - 5 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Yin, Zhong A1 - Rajkovic, Ivan A1 - Kubicek, Katharina A1 - Quevedo, Wilson A1 - Pietzsch, Annette A1 - Wernet, Philippe A1 - Föhlisch, Alexander A1 - Techert, Simone T1 - Probing the Hofmeister effect with ultrafast core-hole spectroscopy JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - In the current work, X-ray emission spectra of aqueous solutions of different inorganic salts within the Hofmeister series are presented. The results reflect the direct interaction of the ions with the water molecules and therefore, reveal general properties of the salt-water interactions. Within the experimental precision a significant effect of the ions on the water structure has been observed but no ordering according to the structure maker/structure breaker concept could be mirrored in the results indicating that the Hofmeister effect if existent may be caused by more complex interactions. Y1 - 2014 U6 - https://doi.org/10.1021/jp504577a SN - 1520-6106 VL - 118 IS - 31 SP - 9398 EP - 9403 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schreck, Simon A1 - Pietzsch, Annette A1 - Kunnus, Kristjan A1 - Kennedy, Brian A1 - Quevedo, Wilson A1 - Miedema, Piter S. A1 - Wernet, Philippe A1 - Föhlisch, Alexander T1 - Dynamics of the OH group and the electronic structure of liquid alcohols JF - Structural dynamics N2 - In resonant inelastic soft x-ray scattering (RIXS) from molecular and liquid systems, the interplay of ground state structural and core-excited state dynamical contributions leads to complex spectral shapes that partially allow for ambiguous interpretations. In this work, we dissect these contributions in oxygen K-edge RIXS from liquid alcohols. We use the scattering into the electronic ground state as an accurate measure of nuclear dynamics in the intermediate core-excited state of the RIXS process. We determine the characteristic time in the core-excited state until nuclear dynamics give a measurable contribution to the RIXS spectral profiles to tau(dyn) = 1.2 +/- 0.8 fs. By detuning the excitation energy below the absorption resonance we reduce the effective scattering time below sdyn, and hence suppress these dynamical contributions to a minimum. From the corresponding RIXS spectra of liquid methanol, we retrieve the "dynamic-free" density of states and find that it is described solely by the electronic states of the free methanol molecule. From this and from the comparison of normal and deuterated methanol, we conclude that the split peak structure found in the lone-pair emission region at non-resonant excitation originates from dynamics in the O-H bond in the core-excited state. We find no evidence that this split peak feature is a signature of distinct ground state structural complexes in liquid methanol. However, we demonstrate how changes in the hydrogen bond coordination within the series of linear alcohols from methanol to hexanol affect the split peak structure in the liquid alcohols. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. Y1 - 2014 U6 - https://doi.org/10.1063/1.4897981 SN - 2329-7778 VL - 1 IS - 5 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Miedema, P. S. A1 - Beye, Martin A1 - Koennecke, R. A1 - Schiwietz, G. A1 - Föhlisch, Alexander T1 - The angular- and crystal-momentum transfer through electron-phonon coupling in silicon and silicon-carbide: similarities and differences JF - New journal of physics : the open-access journal for physics N2 - Electron-phonon scattering has been studied for silicon carbide (6H-SiC) with resonant inelastic x-ray scattering at the silicon 2p edge. The observed electron-phonon scattering yields a crystal momentum transfer rate per average phonon in 6H-SiC of 1.8 fs(-1) while it is 0.2 fs(-1) in crystalline silicon. The angular momentum transfer rate per average phonon for 6H-SiC is 0.1 fs(-1), which is much higher than 0.0035 fs(-1) obtained for crystalline silicon in a previous study. The higher electron-phonon scattering rates in 6H-SiC are a result of the larger electron localization at the silicon atoms in 6H-SiC as compared to crystalline silicon. While delocalized valence electrons can screen effectively (part of) the electron-phonon interaction, this effect is suppressed for 6H-SiC in comparison to crystalline silicon. Smaller contributions to the difference in electron-phonon scattering rates between 6H-SiC and silicon arise from the lower atomic mass of carbon versus silicon and the difference in local symmetry. KW - electron-phonon scattering KW - 6H-SiC KW - RIXS Y1 - 2014 U6 - https://doi.org/10.1088/1367-2630/16/9/093056 SN - 1367-2630 VL - 16 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Schreck, Simon A1 - Beye, Martin A1 - Sellberg, Jonas A. A1 - McQueen, Trevor A1 - Laksmono, Hartawan A1 - Kennedy, Brian A1 - Eckert, Sebastian A1 - Schlesinger, Daniel A1 - Nordlund, Dennis A1 - Ogasawara, Hirohito A1 - Sierra, Raymond G. A1 - Segtnan, Vegard H. A1 - Kubicek, Katharina A1 - Schlotter, William F. A1 - Dakovski, Georgi L. A1 - Moeller, Stefan P. A1 - Bergmann, Uwe A1 - Techert, Simone A1 - Pettersson, Lars G. M. A1 - Wernet, Philippe A1 - Bogan, Michael J. A1 - Harada, Yoshihisa A1 - Nilsson, Anders A1 - Föhlisch, Alexander T1 - Reabsorption of soft x-ray emission at high x-ray free-electron laserfluences JF - Physical review letters N2 - We report on oxygen K-edge soft x-ray emission spectroscopy from a liquid water jet at the Linac Coherent Light Source. We observe significant changes in the spectral content when tuning over a wide range of incident x-ray fluences. In addition the total emission yield decreases at high fluences. These modifications result from reabsorption of x-ray emission by valence-excited molecules generated by the Auger cascade. Our observations have major implications for future x-ray emission studies at intense x-ray sources. We highlight the importance of the x-ray pulse length with respect to the core-hole lifetime. Y1 - 2014 U6 - https://doi.org/10.1103/PhysRevLett.113.153002 SN - 0031-9007 SN - 1079-7114 VL - 113 IS - 15 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Miedema, Piter Sybren A1 - Beye, Martin A1 - Koennecke, R. A1 - Schiwietz, Gregor A1 - Föhlisch, Alexander T1 - Thermal evolution of the band edges of 6H-SiC: X-ray methods compared to the optical band gap JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - The band gap of semiconductors like silicon and silicon carbide (SIC) is the key for their device properties. In this research, the band gap of 6H-SiC and its temperature dependence were analyzed with silicon 2p X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) allowing for a separate analysis of the conduction-band minimum (CBM) and valence-band maximum (VBM) components of the band gap. The temperature-dependent asymmetric band gap shrinking of 6H-SiC was determined with a valence-band slope of +2.45 x 10(-4) eV/K and a conduction-band slope of -1.334 x 10(-4) eV/K. The apparent asymmetry, e.g., that two thirds of the band-gap shrinking with increasing temperature is due to the VBM evolution in 6H-SiC, is similar to the asymmetry obtained for pure silicon before. The overall band gap temperature-dependence determined with XAS and nonresonant XES is compared to temperature-dependent optical studies. The core-excitonic binding energy appearing in the Si 2p XAS is extracted as the main difference. In addition, the energy loss of the onset of the first band in RIXS yields to values similar to the optical band gap over the tested temperature range. (C) 2014 Elsevier B.V. All rights reserved. KW - RIXS KW - XAS KW - XES KW - Semiconductors KW - Silicon carbide Y1 - 2014 U6 - https://doi.org/10.1016/j.elspec.2014.08.003 SN - 0368-2048 SN - 1873-2526 VL - 197 SP - 37 EP - 42 PB - Elsevier CY - Amsterdam ER -