The diffusion of individual Pd adatoms on the (110), (211) and (111) surfaces of W was investigated by means of field ion microscopy. As well as monitoring the diffusion of single atoms across perfectly defined single-crystal terraces, a study was made of the diffusion of atoms in the vicinity of surface steps. The behavior of an adatom which approached the step from the upper terrace was also studied. The extra reflective barriers for the step-down motion of Pd atoms on (110), (211) and (111) surfaces were determined to be 0.27, 0.29 and 0.61eV, respectively. The behavior of adatoms which approached the step from the lower terrace was also studied. The activation energy for the step-up motion of Pd atoms at (111) steps was deduced to be 1.84eV. The potential energy of moving towards the (111) pole of the tip exhibited a free-energy anisotropy of 0.013eV/4.47Å.

T.Y.Fu, L.C.Cheng, Y.J.Hwang, T.T.Tseng: Surface Science, 2002, 507-510, 103-7