Surface structure determination by x-ray standing waves at a free-electron laser

G Mercurio,I A Makhotkin,I A Zaluzhnyy,W Wurth,L Wenthaus,I A Vartanyants,I Milov,S Dziarzhytski,Y Y Kim

doi:10.1088/1367-2630/aafa47

Abstract

We demonstrate the structural sensitivity and accuracy of the x-ray standing wave technique at a high repetition rate free-electron laser, FLASH at DESY in Hamburg, by measuring the photoelectron yield from the surface SiO2 of Mo/Si multilayers. These experiments open up the possibility to obtain unprecedented structural information of adsorbate and surface atoms with picometer spatial and femtosecond temporal resolution. This technique will substantially contribute to a fundamental understanding of chemical reactions at catalytic surfaces and the structural dynamics of superconductors.

Highlights

The use of renewable energies for heterogeneous catalysis imposes the understanding of catalytic processes under dynamic reaction conditions
With the advent of x-ray freeelectron lasers (XFEL) [2,3,4,5,6], delivering femtosecond, extremely brilliant, and coherent pulses in the soft and hard x-ray range, it became possible to explore the ultrafast dynamics of heterogeneous catalysis using a pumpprobe approach [7, 8]
To measure the time-resolved structure of reactants and catalysts as the reaction proceeds at the surface, we propose to combine photoelectron spectroscopy with the structural accuracy of the x-ray standing wave (XSW) technique [17,18,19,20] and the time resolution provided by an XFEL

Summary

Introduction

The use of renewable energies for heterogeneous catalysis imposes the understanding of catalytic processes under dynamic reaction conditions. XFEL probe pulses are used to measure time-resolved x-ray absorption and emission spectra In this way several elementary processes, essential for understanding more complex chemical reactions, were unveiled: breaking of the bond between CO molecules and a Ru surface [10], transient excitation of O atoms out of their ground adsorption state [11], transient states of CO oxidation [7], and hydrogenation reactions [8]. The interpretation of these spectroscopic data relies on density functional theory (DFT) calculations. A direct structural information on the position of atoms and molecules during the reaction is still missing

Results

Discussion

Conclusion