Direct evidence for the effect of local strain at a surface on the bonding strength for adsorbates is presented. Scanning tunneling microscopy revealed that adsorbed oxygen atoms on Ru(0001) surfaces are located preferentially on top of nanometer-size protrusions above subsurface argon bubbles, where tensile strain prevails, and are depleted around their rim in regions of compression, relative to the flat surface. Such effects can be considered as the reverse of adsorbate-induced strain, and their direct local demonstration can be used to test theoretical predictions.

Using scanning tunneling microscopy the effect of local strain at a Ru(001) surface on the adsorption of various adsorbates has been studied. Local strain fields have been produced by Ar-ion implantation and annealing. Thereby the accompanying surface sputter damage is fully healed out with the exception of subsurface cavities filled with argon atoms which have aggregated by bulk diffusion. The resulting nanometer-sized structures contain surface areas of expanded lattice at the tops of the protrusions while around their rim the lattice is compressed relative to the flat surface. Various adsorbates are found to react sensitively to these local lattice distortions. Oxygen atoms adsorb preferentially in the regions of expanded lattice. This preference prevails for all coverages up to the full monolayer with the successive formation of the well-known (2×2)-O, (2×1)-O, (2×2)-3O, and (1×1)-O ordered overlayers on the various parts of the surface. CO at coverages in excess of 0.33 monolayers is found to behave similarly. The experimental results are complemented by investigations of the mixed (O+CO) coadsorbate layer. The reported influence of surface strain on the adsorption energy can be considered as the reverse of strain induction by adsorption, and their direct local demonstration can be used to test theoretical predictions. We also find direct evidence for a compressed lattice zone close to step edges, which extends about 10–20 Å into the terraces.

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A detailed low‐energy electron diffraction (LEED)‐IV analysis, complemented by scanning tunneling microscopy (STM) observations, was carried out for the apparent (2 × 2) structure of the oxygen‐covered Ru(001) surface at a coverage of 0.75 ML. We present STM images of incomplete layers which allow one to define the symmetry of the ordered layer, in particular of the novel high density p(2 × 2)‐3O phase. In the LEED‐IV analysis we have tested 28 model structures; the results can be used for conclusions about the discrimination of this type of geometry determination. Our quantitative LEED analysis in connection with the STM results corroborates the model proposed before and shows that all of the oxygen atoms sit in the hcp sites with an averaged vertical distance to the outermost Ru layer of d⊥Ru–O = 1.22 Å. This value falls into the general trend of increasing d⊥Ru–O with oxygen coverage observed for the other ordered structures of adsorbed oxygen on Ru and is also predicted by recent total energy calculations. The O–Ru bonding distance of about 2.0 Å is essentially unchanged compared to the other structures. Considerable lateral and vertical displacements of both the O and the Ru atoms are found, with the O atoms being slightly displaced towards the fcc hollow site located in the center of three oxygen atoms. The two uppermost substrate layers are buckled; in the first layer three out of four Ru atoms of the (2 × 2) unit cell are shifted away laterally from their bulk positions. These shifts, globally as well as locally, can be understood in terms of local electron density changes induced by the adsorbed oxygen atoms.

We report photon stimulated resorption (PSD) of neutral and ionic molecules and atoms from CO chemisorbed on Ru(OO1)and Cu(l 11), and from N2 chemisorbed on Ru(OO1).Comparing branching ratios and spectral features for the 01s and Nls regions, we demonstrate that desorbing neutrals and ions are supplementary probes for the entire region of one-and multielectron excitations, bearing valuable information on the transfer of energy and charge. For the primary [Nl s]n" excitation ofN2/Ru(O01 ) we find excitation site-dependent branching into resorption of Nzo, No and~. PSD of neutral N atoms predominates for excitations of the N atom close to the surface, whereas mainly neutral N2 molecules and N+ ions are ejected for excitations of the outer N atom. We analyze the mechanisms of selective bond breaking on the basis of previously obtained atom-selective decay electron spectra. At the Ru3p substrate thresholds we find significant enhancements of the N+ and N2+yields from N2/Ru@Ol), and discuss the electronic nature of the underlying energy transfer mechanism.