@article{SchreckBeyeSellbergetal.2014,
  author    = {Schreck, Simon and Beye, Martin and Sellberg, Jonas A. and McQueen, Trevor and Laksmono, Hartawan and Kennedy, Brian and Eckert, Sebastian and Schlesinger, Daniel and Nordlund, Dennis and Ogasawara, Hirohito and Sierra, Raymond G. and Segtnan, Vegard H. and Kubicek, Katharina and Schlotter, William F. and Dakovski, Georgi L. and Moeller, Stefan P. and Bergmann, Uwe and Techert, Simone and Pettersson, Lars G. M. and Wernet, Philippe and Bogan, Michael J. and Harada, Yoshihisa and Nilsson, Anders and F{\"o}hlisch, Alexander},
  title     = {Reabsorption of soft x-ray emission at high x-ray free-electron laserfluences},
  series = {Physical review letters},
  volume    = {113},
  journal   = {Physical review letters},
  number    = {15},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {0031-9007},
  doi       = {10.1103/PhysRevLett.113.153002},
  pages     = {6},
  year      = {2014},
  abstract  = {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.},
  language  = {en}
}
@article{ObergGladhAnniyevetal.2015,
  author    = {Oberg, H. and Gladh, J{\"o}rgen and Anniyev, Toyli and Beye, Martin and Coffee, Ryan and F{\"o}hlisch, Alexander and Katayama, T. and Kaya, Sarp and LaRue, Jerry and Mogelhoj, Andreas and Nordlund, Dennis and Ogasawara, Hirohito and Schlotter, William F. and Sellberg, Jonas A. and Sorgenfrei, Nomi and Turner, Joshua J. and Wolf, Martin and Wurth, W. and Ostrom, Henrik and Nilsson, Anders and Norskov, Jens K. and Pettersson, Lars G. M.},
  title     = {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},
  series = {Surface science},
  volume    = {640},
  journal   = {Surface science},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0039-6028},
  doi       = {10.1016/j.susc.2015.03.011},
  pages     = {80 -- 88},
  year      = {2015},
  abstract  = {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.},
  language  = {en}
}
@article{Dell'AngelaAnniyevBeyeetal.2015,
  author    = {Dell'Angela, Martina and Anniyev, Toyli and Beye, Martin and Coffee, Ryan and F{\"o}hlisch, Alexander and Gladh, J{\"o}rgen and Kaya, Sarp and Katayama, Tetsuo and Krupin, Oleg and Nilsson, Anders and Nordlund, Dennis and Schlotter, William F. and Sellberg, Jonas A. and Sorgenfrei, Nomi and Turner, Joshua J. and {\"O}str{\"O}m, Henrik and Ogasawara, Hirohito and Wolf, Martin and Wurth, Wilfried},
  title     = {Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer},
  series = {Structural dynamics},
  volume    = {2},
  journal   = {Structural dynamics},
  number    = {2},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {2329-7778},
  doi       = {10.1063/1.4914892},
  pages     = {10},
  year      = {2015},
  abstract  = {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).},
  language  = {en}
}