Atomic jump lengths in surface diffusion: experiment and theory

One-dimensional diffusion by long jumps has recently been found for Pd on W(211). The frequency of long jumps is derived from measurements of the distribution of displacements of a single adatom. The data, corrected for the effect of finite plane size, reveal that 15% of the jumps cover two nearest-neighbor distances and 10% cover three nearest-neighbor distances at 133 K. The long jumps have a pronounced temperature dependence; none are detected at a temperature just 11 K lower. These experimental results are compared with recent predictions based on a Brownian motion theory. It is found that the Brownian model does not adequately describe the temperature dependence of the experimental results.