TRAPPING OF A DIFFUSING ADATOM BY A SUBSTITUTIONAL SURFACE DEFECT

We propose a simple model to explain qualitatively the results of a recent field-ion-microscopy (FIM) study in which a substitutional Ir atom in the Rh(001) surface traps diffusing Rh adatoms [G.L. Kellogg, Phys. Rev. Lett., to be published]. The proposed explanation is supported by an embedded-atom-method investigation of the effect of a substitutional Pt atom in the Pd(001) surface on Pd adatom diffusion. We find a smaller energy barrier for a single adatom to diffuse around the defect than away from it, i.e., the adatom is effectively trapped by this defect in qualitative agreement with the FIM study. We also find that Pd adatom clusters are more strongly bound at the defect than away from it, indicating that such a defect can act as a nucleation site for cluster growth.