DIRECT OBSERVATION OF SUBSTITUTIONAL-ATOM TRAPPING ON A METAL-SURFACE

Field ion microscope observations show that individual Rh adatoms on the Rh(100) surface are trapped in the four lattice sites adjacent to an Ir substitutional atom intentionally embedded into the surface. The activation barrier for the Rh adatom to escape from the impurity trap is 0.95 eV, considerably higher than the self-diffusion barrier on the defect-free surface (0.83 eV). The activation barrier to move between the four equivalent trap sites is 0.76 eV. The increased binding along with a higher Rh desorption field at the trap sites imply a stronger Ir-Rh bond compared to Rh-Rh.