Diffusion of Ir-dimers on Ir(110) surfaces by atomic-exchange and atomic-hopping mechanisms

Abstract

Abstract On the Ir(110) surface, single Ir adatoms and Ir-dimers can diffuse along the [110] surface channels as well as across these channels. The latter diffusion most probably occurs by an atomic-exchange mechanism. The visited-site-lattice for both Ir and Ir 2 is found to be the (1 × 1) net of the substrate lattice. From a measurement of the two-dimensional displacement distributions and comparing them with Monte Carlo simulations we conclude that atomic jumps extend only to the nearest-neighbor sites. For single Ir-adatoms, diffusion across the channels is easier than along the channels. For Ir-dimers the along-channel diffusion is easier. The energies needed for single Ir-atoms and Ir-dimers to hop along the channel and to displace across the channel by atomic exchanges are derived. The binding energy of the dimer is measured to be 1.10 ± 0.11 eV which is exceptionally high for a metallic dimer on a metal surface. This large dimer binding energy leads us to believe that on the Ir(110) surface an Ir-dimer diffuses by concerted jumps of the two atoms, and the (1 × 2) surface reconstruction of this surface is achieved by diffusion of small atomic clusters.