ADSORPTION SITES AND DIFFUSION STEPS OF IN AND CD ON PD(111) SURFACES

Adsorption sites of isolated 111In and 111mCd atoms evaporated onto Pd(111) surfaces and their diffusion behaviour were investigated as a function of temperature. Using the perturbed γγ angular correlation technique (PAC) different adsorption sites could be characterized by the hyperfine interaction of the electric field gradient (EFG) with the nuclear quadrupole moment of the radioactive probe nuclei. Five adsorption sites successively occupied by the adatoms during annealing between 80 and 600 K could be identified. The first site may be attributed to In atoms occupying terrace sites on top of the first Pd layer moving to step sites already below 120 K. On vicinal Pd(111) surfaces In and Cd atoms behave very similar, successively occupying step sites, kink sites and substitutional step sites during isochronal annealing. Above 380 K both probe atoms take up substitutional terrace sites replacing a Pd atom in the first layer. From the temperature of conversion between different sites approximate values for activation energies could be estimated. The data can consistently be explained with an activation energy of Ea = 0.76(8)eV for Pd surface self-diffusion. © 1990.