Surface core-level shifts of clean and oxygen-covered Ru(0001)

Abstract

We have performed high resolution XPS experiments of the Ru(0001) surface, both clean and covered with well-defined amounts of oxygen up to 1 ML coverage. For the clean surface we detected two distinct components in the Ru 3d 5/2 core level spectra, for which a definite assignment was made using the high resolution Angle-Scan Photoelectron Diffraction approach. For the p(2 × 2), p(2 × 1), (2 × 2)-3O and (1 × 1)-O oxygen structures we found Ru 3d 5/2 core level peaks which are shifted up to 1 eV to higher binding energies. Very good agreement with density functional theory calculations of these Surface Core Level Shifts (SCLS) is reported. The overriding parameter for the resulting Ru SCLSs turns out to be the number of directly coordinated O atoms. Since the calculations permit the separation of initial and final state effects, our results give valuable information for the understanding of bonding and screening at the surface, otherwise not accessible in the measurement of the core level energies alone.

O- and H-induced surface core level shifts on Ru(0001): prevalence of the additivity rule

“…In view of a potential application to less well characterized systems more general relations enabling a direct data interpretation are therefore of interest. In this respect, the mentioned SCLS work at Rh(111) [3] and Ru(0001) [4] identified an intriguing scaling in that the O-induced SCLSs of the first-layer metal atoms turned out to be linearly proportional to the number of directly coordinated O atoms to good accuracy. With the induced SCLS containing only a small and not much coverage dependent final-state contribution, the source of this additiv-ity could be traced back to a roughly constant amount of charge that is withdrawn from the surface atoms by each directly coordinated O neighbor [4].…”

“…In this respect, the mentioned SCLS work at Rh(111) [3] and Ru(0001) [4] identified an intriguing scaling in that the O-induced SCLSs of the first-layer metal atoms turned out to be linearly proportional to the number of directly coordinated O atoms to good accuracy. With the induced SCLS containing only a small and not much coverage dependent final-state contribution, the source of this additiv-ity could be traced back to a roughly constant amount of charge that is withdrawn from the surface atoms by each directly coordinated O neighbor [4]. With ensuing work on Rh(100) confirming this then termed "additivity rule", it was suggested that the latter may be a universal property of SCLSs which could be used for the fingerprinting of adsorbate populations in catalytic applications [2].…”

“…[4]. The SuperESCA beamline of the synchrotron radiation source ELETTRA in Trieste was used which works at base pressures in the low 10 −10 mbar region and contains preparation facilities and an electron spectrometer with multichannel detection.…”

“…The SuperESCA beamline of the synchrotron radiation source ELETTRA in Trieste was used which works at base pressures in the low 10 −10 mbar region and contains preparation facilities and an electron spectrometer with multichannel detection. The Ru(0001) surface was prepared by established procedures [4,6,7,9]; cleanliness and order of the surface were checked by XPS and low-energy electron diffraction (LEED). The following adsorbate structures have been investigated:…”

“…To this end we have selected H atom adsorption and O + H coadsorption on Ru(0001). This choice has the advantage that not only O [4,6] and H [7] atomic overlayers, but also two well-defined (O+H) coadsorbate systems [8,9] have already been characterized in detail in terms of adsorbate phases and geometries. On this basis we have measured the SCLS spectra for these systems and combined them with DFT calculations for ground state energies, geometries, electronic structure, and SCLS values for the various distinguishable Ru surface atoms.…”