Dynamical behavior and energetics of the Ir(001) surface.

Abstract

An atomic view of the dynamical behavior of the Ir(001) surface is presented. The atomic processes involved in the dissolution of the surface layer are isolated and their mechanisms and energetics are studied quantitatively. Above 400 K, lattice-step atoms can move along the steps, mostly along the 〈110〉 steps, and step atoms can also dissociate to the terraces. By diffusion, dissociation, and reabsorption of step atoms, 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〉 closely packed atomic-row directions. Step atoms dissociate from edge sites, kink sites, ledge sites, and recessed sites with a comparable probability; thus the dissociation is not orderly and the steps are roughened above \ensuremath{\sim}500 K. We measure the diffusion energy of ledge-site atoms along the 〈110〉 lattice steps to be 0.62 eV. This diffusion 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 measured to be 1.35\ifmmode\pm\else\textpm\fi{}0.08 and 1.40\ifmmode\pm\else\textpm\fi{}0.07 eV, respectively. The line-energy density of the 〈110〉 step is (3.2\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ J/m and the self-adsorption energy is 6.37\ifmmode\pm\else\textpm\fi{}0.09 eV. We also find hollow clusters and ``spongelike'' two-dimensional surface layers on the Ir(001) surface.