The diffusion of platinum adatoms and dimers on Pt(111) has been measured at different temperatures by direct observation in a low-temperature field ion microscope. The activation energy for single atom motion is found to be 0.260±0.003 eV, while for dimers it is 0.37±0.02 eV. Comparison with previous results obtained in STM studies of the density of islands after deposition from the vapor as well as with theoretical estimates are now possible. The former are in excellent agreement, the latter less so, but empirical extrapolation from the neighboring iridium proves useful. Contributions from dimer diffusion to growth at low temperatures can also be assessed, and are found to be minor.
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