@article{Dell'AngelaAnniyevBeyeetal.2013,
  author    = {Dell'Angela, M. and Anniyev, Toyli and Beye, Martin and Coffee, Ryan and F{\"o}hlisch, Alexander and Gladh, J. and Katayama, T. and Kaya, S. and Krupin, O. and LaRue, J. and Mogelhoj, A. and Nordlund, D. and Norskov, J. K. and Oberg, H. and Ogasawara, H. and Ostrom, H. and Pettersson, Lars G. M. and Schlotter, W. F. and Sellberg, J. A. and Sorgenfrei, Florian and Turner, J. J. and Wolf, M. and Wurth, W. and Nilsson, A.},
  title     = {Real-time observation of surface bond breaking with an X-ray Laser},
  series = {Science},
  volume    = {339},
  journal   = {Science},
  number    = {6125},
  publisher = {American Assoc. for the Advancement of Science},
  address   = {Washington},
  issn      = {0036-8075},
  doi       = {10.1126/science.1231711},
  pages     = {1302 -- 1305},
  year      = {2013},
  abstract  = {We used the Linac Coherent Light Source free-electron x-ray laser to probe the electronic structure of CO molecules as their chemisorption state on Ru(0001) changes upon exciting the substrate by using a femtosecond optical laser pulse. We observed electronic structure changes that are consistent with a weakening of the CO interaction with the substrate but without notable desorption. A large fraction of the molecules (30\%) was trapped in a transient precursor state that would precede desorption. We calculated the free energy of the molecule as a function of the desorption reaction coordinate using density functional theory, including van der Waals interactions. Two distinct adsorption wells-chemisorbed and precursor state separated by an entropy barrier-explain the anomalously high prefactors often observed in desorption of molecules from metals.},
  language  = {en}
}
@article{deJongKukrejaTrabantetal.2013,
  author    = {de Jong, S. and Kukreja, R. and Trabant, C. and Pontius, N. and Chang, C. F. and Kachel, T. and Beye, Martin and Sorgenfrei, Florian and Back, C. H. and Braeuer, B. and Schlotter, W. F. and Turner, J. J. and Krupin, O. and Doehler, M. and Zhu, D. and Hossain, M. A. and Scherz, A. O. and Fausti, D. and Novelli, F. and Esposito, M. and Lee, W. S. and Chuang, Y. D. and Lu, D. H. and Moore, R. G. and Yi, M. and Trigo, M. and Kirchmann, P. and Pathey, L. and Golden, M. S. and Buchholz, Marcel and Metcalf, P. and Parmigiani, F. and Wurth, W. and F{\"o}hlisch, Alexander and Schuessler-Langeheine, Christian and Duerr, H. A.},
  title     = {Speed limit of the insulator-metal transition in magnetite},
  series = {Nature materials},
  volume    = {12},
  journal   = {Nature materials},
  number    = {10},
  publisher = {Nature Publ. Group},
  address   = {London},
  issn      = {1476-1122},
  doi       = {10.1038/NMAT3718},
  pages     = {882 -- 886},
  year      = {2013},
  abstract  = {As the oldest known magnetic material, magnetite (Fe3O4) has fascinated mankind for millennia. As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown(1), magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator-metal, or Verwey, transition has long remained inaccessible(2-8). Recently, three- Fe- site lattice distortions called trimeronswere identified as the characteristic building blocks of the low-temperature insulating electronically ordered phase(9). Here we investigate the Verwey transition with pump- probe X- ray diffraction and optical reflectivity techniques, and show how trimerons become mobile across the insulator-metal transition. We find this to be a two- step process. After an initial 300 fs destruction of individual trimerons, phase separation occurs on a 1.5 +/- 0.2 ps timescale to yield residual insulating and metallic regions. This work establishes the speed limit for switching in future oxide electronics(10).},
  language  = {en}
}
@article{BeyeSchreckSorgenfreietal.2013,
  author    = {Beye, Martin and Schreck, S. and Sorgenfrei, Florian and Trabant, C. and Pontius, N. and Sch{\"u}ßler-Langeheine, C. and Wurth, W. and F{\"o}hlisch, Alexander},
  title     = {Stimulated X-ray emission for materials science},
  series = {Nature : the international weekly journal of science},
  volume    = {501},
  journal   = {Nature : the international weekly journal of science},
  number    = {7466},
  publisher = {Nature Publ. Group},
  address   = {London},
  issn      = {0028-0836},
  doi       = {10.1038/nature12449},
  pages     = {191 -- +},
  year      = {2013},
  abstract  = {Resonant inelastic X-ray scattering and X-ray emission spectroscopy can be used to probe the energy and dispersion of the elementary low-energy excitations that govern functionality in matter: vibronic, charge, spin and orbital excitations(1-7). A key drawback of resonant inelastic X-ray scattering has been the need for high photon densities to compensate for fluorescence yields of less than a per cent for soft X-rays(8). Sample damage from the dominant non-radiative decays thus limits the materials to which such techniques can be applied and the spectral resolution that can be obtained. A means of improving the yield is therefore highly desirable. Here we demonstrate stimulated X-ray emission for crystalline silicon at photon densities that are easily achievable with free-electron lasers(9). The stimulated radiative decay of core excited species at the expense of non-radiative processes reduces sample damage and permits narrow-bandwidth detection in the directed beam of stimulated radiation. We deduce how stimulated X-ray emission can be enhanced by several orders of magnitude to provide, with high yield and reduced sample damage, a superior probe for low-energy excitations and their dispersion in matter. This is the first step to bringing nonlinear X-ray physics in the condensed phase from theory(10-16) to application.},
  language  = {en}
}
@article{KatayamaAnniyevBeyeetal.2013,
  author    = {Katayama, T. and Anniyev, Toyli and Beye, Martin and Coffee, Ryan and Dell'Angela, M. and F{\"o}hlisch, Alexander and Gladh, J. and Kaya, S. and Krupin, O. and Nilsson, A. and Nordlund, D. and Schlotter, W. F. and Sellberg, J. A. and Sorgenfrei, Florian and Turner, J. J. and Wurth, W. and {\"O}str{\"o}m, H. and Ogasawara, H.},
  title     = {Ultrafast soft X-ray emission spectroscopy of surface adsorbates using an X-ray free electron laser},
  series = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy},
  volume    = {187},
  journal   = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy},
  number    = {1},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0368-2048},
  doi       = {10.1016/j.elspec.2013.03.006},
  pages     = {9 -- 14},
  year      = {2013},
  abstract  = {We report on an experimental system designed to probe chemical reactions on solid surfaces on a sub-picosecond timescale using soft X-ray emission spectroscopy at the Linac Coherent Light Source (LCLS) free electron laser (FEL) at the SLAC National Accelerator Laboratory. We analyzed the O 1s X-ray emission spectra recorded from atomic oxygen adsorbed on a Ru(0001) surface at a synchrotron beamline (SSRL, BL13-2) and an FEL beamline (LCLS, SXR). We have demonstrated conditions that provide negligible amount of FEL induced damage of the sample. In addition we show that the setup is capable of tracking the temporal evolution of electronic structure during a surface reaction of submonolayer quantities of CO molecules desorbing from the surface.},
  language  = {en}
}