Interactions of adsorbates with locally strained substrate lattices

Using scanning tunneling microscopy the effect of local strain at a Ru(001) surface on the adsorption of various adsorbates has been studied. Local st rain fields have been produced by Ar-ion implantation and annealing. Thereb y the accompanying surface sputter damage is fully healed out with the exce ption 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 thei r rim the lattice is compressed relative to the flat surface. Various adsor bates are found to react sensitively to these local lattice distortions. Ox ygen atoms adsorb preferentially in the regions of expanded lattice. This p reference prevails for all coverages up to the full monolayer with the succ essive formation of the well-known (2x2)-O, (2x1)-O, (2x2)-3O, and (1x1)-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 re sults are complemented by investigations of the mixed (O+CO) coadsorbate la yer. The reported influence of surface strain on the adsorption energy can be considered as the reverse of strain induction by adsorption, and their d irect local demonstration can be used to test theoretical predictions. We a lso find direct evidence for a compressed lattice zone close to step edges, which extends about 10-20 Angstrom into the terraces. (C) 2001 American In stitute of Physics.