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Using field ion microscopy, we probe the diffusion behavior of Pd adatoms on the W (111) surface and also in the vicinity of the surface step. An adatom approaching the step from the upper terrace is reflected by the step boundary with an extra reflective barrier of 0.61±0.01 eV. The behavior of an adatom approaching the step from the lower terrace is also studied. The activation energy for the step-up motion of a Pd atom at the W (111) step edge is 1.84±0.07 eV. The potential energy difference toward and away from the W (111) pole due to a free energy anisotropy is 0.013 eV/4.47 Å. Our energetic data for surface atomic processes are useful for understanding the impurity induced pyramidal facet formation.