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

SURFACE SCIENCE

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Article

Oberg, H.¹  Gladh, J.¹  Dell'Angela, M.^2,3  Anniyev, T.⁴  Beye, M.⁵  Coffee, R.⁶  Foehlisch, A.⁷  Katayama, T.⁴  Kaya, S.⁴  LaRue, J.⁴  Mogelhoj, A.^8,9  Nordlund, D.¹⁰  Ogasawara, H.¹⁰  Schlotter, W. F.⁶  Sellberg, J. A.^1,4  Sorgenfrei, F.^2,3  Turner, J. J.⁶  Wolf, M.¹²  Wurth, W.^2,3  Ostrom, H.¹  Nilsson, A.^1,4,8,10  Norskov, J. K.^8,11  Pettersson, L. G. M.¹ 

[1] Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden

[2] Univ Hamburg, D-22761 Hamburg, Germany

[3] Ctr Free Electron Laser Sci, D-22761 Hamburg, Germany

[4] SIMES, SLAC Natl Accelerator Lab, Menlo Pk, CA 94025 USA

[5] Helmholtz Zentrum Berlin Mat & Energie GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, D-12489 Berlin, Germany

[6] SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA

[7] Univ Potsdam, Inst Phys & Astron, D-14476 Potsdam, Germany

[8] SLAC Natl Accelerator Lab, SUNCAT Ctr Interface Sci & Catalysis, Menlo Pk, CA 94025 USA

[9] Tech Univ Denmark, Dept Phys, CAMD, DK-2800 Lyngby, Denmark

[10] SLAC Natl Accelerator Lab, Stanford Synchrotron Radiat Lightsource, Menlo Pk, CA 94025 USA

[11] Stanford Univ, Dept Chem Engn, SUNCAT Ctr Interface Sci & Catalysis, Stanford, CA 95305 USA

[12] Max Planck Gesell, Fritz Haber Inst, D-14195 Berlin, Germany

关键词: CO desorption;    Potential of mean force;    Two-temperature model;    Pump-probe;    X-ray spectroscopy;    Density functional theory;   

DOI  :  10.1016/j.susc.2015.03.011

来源: Elsevier

【 摘 要 】

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.

【 授权许可】

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