ATOMIC VIEW OF THE UPWARD MOVEMENT OF STEP-EDGE AND IN-LAYER ATOMS OFIR SURFACES

The behavior of adatoms, step-edge atoms, and in-layer atoms at high t emperature plays an important role in determining the growth mode of e pitaxial thin films and crystals, the crystal shape change, and the mo rphology of crystal surfaces. From a direct field ion microscope obser vation, 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 low er terrace. The activation barrier height for the ascending motion is measured to be 1.51 +/- 0.10 eV, whereas the dissociation barrier is s imilar to 1.6 +/- 0.2 eV. Surprisingly, we also find that in-layer ato ms can jump up to terrace sites, thus forming adatom-vacancy complexes , at unexpectedly low temperatures.