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  - Oberg, H.
A1  - Gladh, Jörgen
A1  - Anniyev, Toyli
A1  - Beye, Martin
A1  - Coffee, Ryan
A1  - Föhlisch, Alexander
A1  - Katayama, T.
A1  - Kaya, Sarp
A1  - LaRue, Jerry
A1  - Mogelhoj, Andreas
A1  - Nordlund, Dennis
A1  - Ogasawara, Hirohito
A1  - Schlotter, William F.
A1  - Sellberg, Jonas A.
A1  - Sorgenfrei, Nomi
A1  - Turner, Joshua J.
A1  - Wolf, Martin
A1  - Wurth, W.
A1  - Ostrom, Henrik
A1  - Nilsson, Anders
A1  - Norskov, Jens K.
A1  - Pettersson, Lars G. M.
T1  - Optical laser-induced CO desorption from Ru(0001) monitored with a free-electron X-ray laser: DFT prediction and X-ray confirmation of a precursor state
JF  - Surface science
N2  - We present density functional theory modeling of time-resolved optical pump/X-ray spectroscopic probe data of CO desorption from Ru(0001). The BEEF van der Waals functional predicts a weakly bound state as a precursor to desorption. The optical pump leads to a near-instantaneous (<100 fs) increase of the electronic temperature to nearly 7000 K. The temperature evolution and energy transfer between electrons, substrate phonons and adsorbate is described by the two-temperature model and found to equilibrate on a timescale of a few picoseconds to an elevated local temperature of similar to 2000K. Estimating the free energy based on the computed potential of mean force along the desorption path, we find an entropic barrier to desorption (and by time-reversal also to adsorption). This entropic barrier separates the chemisorbed and precursor states, and becomes significant at the elevated temperature of the experiment (similar to 1.4 eV at 2000 K). Experimental pump-probe X-ray absorption/X-ray emission spectroscopy indicates population of a precursor state to desorption upon laser-excitation of the system (Dell'Angela et al., 2013). Computing spectra along the desorption path confirms the picture of a weakly bound transient state arising from ultrafast heating of the metal substrate. (C) 2015 Elsevier B.V. All rights reserved.
KW  - CO desorption
KW  - Potential of mean force
KW  - Two-temperature model
KW  - Pump-probe
KW  - X-ray spectroscopy
KW  - Density functional theory
Y1  - 2015
U6  - https://doi.org/10.1016/j.susc.2015.03.011
SN  - 0039-6028
SN  - 1879-2758
VL  - 640
SP  - 80
EP  - 88
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Dell'Angela, Martina
A1  - Anniyev, Toyli
A1  - Beye, Martin
A1  - Coffee, Ryan
A1  - Föhlisch, Alexander
A1  - Gladh, Jörgen
A1  - Kaya, Sarp
A1  - Katayama, Tetsuo
A1  - Krupin, Oleg
A1  - Nilsson, Anders
A1  - Nordlund, Dennis
A1  - Schlotter, William F.
A1  - Sellberg, Jonas A.
A1  - Sorgenfrei, Nomi
A1  - Turner, Joshua J.
A1  - ÖstrÖm, Henrik
A1  - Ogasawara, Hirohito
A1  - Wolf, Martin
A1  - Wurth, Wilfried
T1  - Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer
JF  - Structural dynamics
N2  - Vacuum space charge induced kinetic energy shifts of O 1s and Ru 3d core levels in femtosecond soft X-ray photoemission spectra (PES) have been studied at a free electron laser (FEL) for an oxygen layer on Ru(0001). We fully reproduced the measurements by simulating the in-vacuum expansion of the photoelectrons and demonstrate the space charge contribution of the high-order harmonics in the FEL beam. Employing the same analysis for 400 nm pump-X-ray probe PES, we can disentangle the delay dependent Ru 3d energy shifts into effects induced by space charge and by lattice heating from the femtosecond pump pulse. (C) 2015 Author(s).
Y1  - 2015
U6  - https://doi.org/10.1063/1.4914892
SN  - 2329-7778
VL  - 2
IS  - 2
PB  - American Institute of Physics
CY  - Melville
ER  -