Adsorption of transition adatoms on a stepped BCC transition-metal surface

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Abstract
The binding energy contour map are calculated for a transition adatom on an (m(110)*(011)) BCC transition-metal surface, taking into account the band term which is treated in the tight-binding approximation and a pairwise repulsive potential of the Born-Mayer type. The binding energy is minimised with respect to the position of the adsorbate relative to the surface, keeping all the atoms involved in the bonding neutral. Two kinds of systems are studied: adatoms of the same chemical species as the substrate and adatoms of the 5d series on a W substrate. One finds that the most stable adsorption site is the ledge one, while the second most stable site is close to the edge of the step. On the other hand, it is shown that an adatom moving towards the step edge sees an extra barrier height, causing its reflection by the step. A comparison with field ion microscopy experiments is made and shows a rather good agreement of the binding and activation energies.