First-principles calculations showed that the barrier to surface self-diffusion via concerted substitution was lower on those transition-metal (100) surfaces where substrate relaxation around an adatom, and the corresponding energy gain, were greater. Stress calculations contradicted the view that lower-barrier concerted substitution corresponded to greater tensile stress reduction along the concerted substitution diffusion path. It was concluded that those metals which most weakly resisted deformation in the presence of a self-adsorbed atom were those on which concerted substitution was the low-barrier diffusion mode. An apparent corollary was that a co-adsorbate which decreased adatom-induced substrate relaxation might also inhibited concerted substitution diffusion. This suggested a means for controlling surface alloy formation in heterogeneous epitaxy (surfactant effect). It was already known that co-adsorbed H raised the concerted substitution barrier to Pt adatom diffusion on the (100)Pt surface; relative to that for hopping.

Adsorption-Induced Lattice Relaxation and Diffusion by Concerted Substitution. P.J.Feibelman, R.Stumpf: Physical Review B, 1999, 59[8], 5892-7