Behavior of Ir atoms and clusters on Ir surfaces

Several aspects of the behavior of single Ir atoms and small Ir atomic clusters on the Ir(100) and Ir(111) surfaces as functions of the temperature have been studied with the atomic-resolution field-ion microscope. From these experiments, diffusion parameters, the dissociation energy of plane edge atoms, and other experimental parameters of interest have been derived. For very small clusters, the probabilities of observing different structures, in general, depend on the temperature. For the three-atom cluster on the Ir(111) the ln(${\mathit{p}}_{1\mathrm{D}}$/${\mathit{p}}_{2\mathrm{D}}$)-vs-(1/T) plot, where ${\mathit{p}}_{1\mathrm{D}}$ and ${\mathit{p}}_{2\mathrm{D}}$ represent, respectively, the probabilities of forming a one- and a two-dimensional structure, is linear. The 2D structure is more stable with a larger effective cluster binding energy of 0.098±0.004 eV. In contrast, for the three-atom Ir cluster on the Ir(100) the plot exhibits two linear sections, one with an effective cluster binding-energy difference of ∼0.335±0.015 eV, and one is equivalent to have an effective cluster binding-energy difference of ∼3.94±0.35 eV. The 1D structure is more stable. We believe that this deviation from the simple linear behavior on the (100) surface is due to the occurrence of a structure phase transition of the three-atom cluster interacting with the substrate, which is a large reservoir containing many atoms. The dissociation energy of plane edge atoms, or the 2D sublimation energy, of the Ir(100) layer is found to be ∼1.4 eV, from which the binding energy of Ir adatoms on the Ir(100) surface is derived to be ∼6.5 eV.