DYNAMICAL BEHAVIOR AND ENERGETICS OF THE IR(001) SURFACE

An atomic view of the dynamical behavior of the Ir(001) surface is pre sented. The atomic processes involved in the dissolution of the surfac e layer are isolated and their mechanisms and energetics are studied q uantitatively. Above 400 K, lattice-step atoms can move along the step s, mostly along the [110] steps, and step atoms can also dissociate to the terraces. By diffusion, dissociation, and reabsorption of step at oms, an equilibrium shape of the surface layer can be achieved, which, around 400 K, is a square with its four sides parallel to the [110] c losely packed atomic-row directions. Step atoms dissociate from edge s ites, kink sites, ledge sites, and recessed sites with a comparable pr obability; thus the dissociation is not orderly and the steps are roug hened above approximately 500 K. We measure the diffusion energy of le dge-site atoms along the [110] lattice steps to be 0.62 eV. This diffu sion occurs by atomic hopping; for comparison, self-diffusion on the ( 001) terrace occurs by atomic replacement in the [001] directions. The dissociation energy of edge-site atoms and other step atoms are measu red to be 1.35+/-0.08 and 1.40+/-0.07 eV, respectively. The line-energ y density of the [110] step is (3.2+/-0.5) X 10(-10) J/m and the self- adsorption energy is 6.37+/-0.09 eV. We also find hollow clusters and ''spongelike'' two-dimensional surface layers on the Ir(001) surface.