Non-Nearest-Neighbor Jumps in 2D Diffusion: Pd on W(110)

A variety of jumps has in the past been identified in diffusion of atoms on 1D channeled surfaces. To establish the jump processes important in diffusion on a 2D surface, the movement of individual Pd atoms has been examined on W(110). From the distribution of displacements of Pd at high temperatures, double jumps are found along the close-packed $〈111〉$. For the first time, sizable differences are also observed between the mean-square displacements along $x$ and $y$, which demonstrate unexpected contributions from jumps along $〈110〉$, but not along $〈001〉$. These jumps proceed over activation barriers higher than for single jumps, under conditions predicted from previous work with Pd on the channeled W(211).