Atomic view of the upward movement of step-edge and in-layer atoms of Ir surfaces

The behavior of adatoms, step-edge atoms, and in-layer atoms at high temperature plays an important role in determining the growth mode of epitaxial thin films and crystals, the crystal shape change, and the morphology of crystal surfaces. From a direct field ion microscope observation, we find that around 500 K an edge atom of the Ir(111) step can ascend the step to the upper terrace as well as dissociate to the lower terrace. The activation barrier height for the ascending motion is measured to be 1.51 +/- 0.10 eV, whereas the dissociation barrier is similar to 1.6 +/- 0.2 eV. Surprisingly, we also find that in-layer atoms can jump up to terrace sites, thus forming adatom-vacancy complexes, at unexpectedly low temperatures.