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

Abstract

In previous work on adsorbate-induced surface core level shifts (SCLSs), the effects caused by O atom adsorption on Rh(111) and Ru(0001) were found to be additive: the measured shifts for first layer Ru atoms depended linearly on the number of directly coordinated O atoms. Densityfunctional theory calculations quantitatively reproduced this effect, allowed separation of initial and final state contributions, and provided an explanation in terms of a roughly constant charge transfer per O atom. We have now conducted similar measurements and calculations for three well-defined adsorbate and coadsorbate layers containing O and H atoms: (1 × 1)-H, (2 × 2)-(O+H), and (2 × 2)-(O+3H) on Ru(0001). As H is stabilized in fcc sites in the prior two structures and in hcp sites in the latter, this enables us to not only study coverage and coadsorption effects on the adsorbate-induced SCLSs, but also the sensitivity to similar adsorption sites. Remarkably good agreement is obtained between experiment and calculations for the energies and geometries of the layers, as well as for all aspects of the SCLS values. The additivity of the next-neighbor adsorbate-induced SCLSs is found to prevail even for the coadsorbate structures. While this confirms the suggested use of SCLSs as fingerprints of the adsorbate configuration, their sensitivity is further demonstrated by the slightly different shifts unambiguously determined for H adsorption in either fcc or hcp hollow sites.

The geometries of coadsorbate layers of O and H on Ru(0 0 1): How well can quantitative LEED see hydrogen atoms?

“…Very recently we have completed theoretical work on these systems [26] which resulted in excellent quantitative agreement with the present results in terms of geometrical and other parameters, corroborating our results and in particular the conclusions about the visibility of H atoms for quantitative LEED.…”

“…Notably, the latter is one monolayer for the sum of O and H atoms in the O + 3H layer. Calculations have shown that the preference of H for fcc over hcp sites in the pure H-layer is only about 2.6% for monolayer coverage [26]. For the dilute (O + H) layer these arguments do not apply; there is ample space, and so the H reverts to its preferred fcc site.…”

Towards an understanding of the chemisorption and catalytic activity of Pd$_{X}$Ru$_{1-X}$ nanoparticles using photoelectron spectroscopy

“…4 (1-6) indicate that the major part of the Ru remains metallic (Ru 0 ) according to component 2. We also observe that below 50 % of Ru molar ratio, we have three additional components at high binding energy [42][43][44][45] corresponding to the Ru 4+ (peak 3), Ru 6+ (peak 4) and Ru 8+ (peak 5), respectively. Clean surface contribution (unsaturated as dangling bonds) corresponding to peak 1 is also observed in these latter samples.…”

“…Figure 5 provides an analytical description about electron exchange processes that occur from one metal to the other and the charge transferred between a metal and a reactant. We also provide details on how the exchange of electrons can be related to the chemisorption TABLE I: Experimentally determined core level binding energy and components for Pd 3d 5/2 and Ru 3p 3/2 from Pd X Ru 1−X (X : 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1) NPs [35,[40][41][42][43][44][45]. process and catalytic activity of NPs.…”

Trends in adsorbate induced core level shifts

“…The SCLS is calculated for an atom coordinated to one (θ = 0.25) and two (θ = 0.5) adsorbates. In previous studies considering some specific systems [16,27,43], it has been reported that the SCLSs scale linearly with surface coverage. The present results generally support this view concerning the reducing adsorbates H and CO.…”