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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

  • 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 ofWe 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.show moreshow less

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Metadaten
Author:H. Oberg, Jörgen Gladh, Toyli Anniyev, M. Beye, R. Coffee, Alexander Foehlisch, T. Katayama, Sarp Kaya, Jerry LaRue, Andreas Mogelhoj, Dennis Nordlund, Hirohito Ogasawara, William F. Schlotter, Jonas A. Sellberg, F. Sorgenfrei, Joshua J. Turner, Martin Wolf, W. Wurth, Henrik Ostrom, Anders Nilsson, Jens K. Norskov, Lars G. M. Pettersson
DOI:https://doi.org/10.1016/j.susc.2015.03.011
ISSN:0039-6028 (print)
ISSN:1879-2758 (online)
Parent Title (English):Surface science
Publisher:Elsevier
Place of publication:Amsterdam
Document Type:Article
Language:English
Year of first Publication:2015
Year of Completion:2015
Release Date:2017/03/27
Tag:CO desorption; Density functional theory; Potential of mean force; Pump-probe; Two-temperature model; X-ray spectroscopy
Volume:640
Pagenumber:9
First Page:80
Last Page:88
Funder:U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering [DE-AC02-76SF00515]; U.S. Department of Energy, Basic Energy Science through the SUNCAT Center for Interface Science and Catalysis; Swedish Research Council [621-2011-4223]; Danish Center for Scientific Computing; Volkswagen Foundation; Alexander von Humboldt Foundation; Lundbeck Foundation; LCLS; Stanford University through the Stanford Institute for Materials Energy Sciences (SIMES); Lawrence Berkeley National Laboratory (LBNL); University of Hamburg through the BMBF priority program FSP 301; Center for Free Electron Laser Science (CFEL)
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie
Peer Review:Referiert