Nanostructure formation on Ir(1 0 0)

Abstract

As a structurally rather flexible surface Ir(1 0 0) can be prepared with different structural phases. The clean and stable phase, Ir(1 0 0)-(5 × 1)-hex, exhibits a quasi-hexagonal top layer arranged in 5-fold periodicity on the square substrate. Also, a hydrogen stabilized phase, Ir(1 0 0)-(5 × 1)-H, with Ir wires of single atomic width and again 5-fold periodicity residing on (1 0 0) layers below can be prepared as well as a bulk-like terminated but metastable phase, Ir(1 0 0)-(1 × 1). The (5 × 1) reconstructed phases offer linear adsorption channels of nanosized width, so that by deposition of other metals linear nanostructures can be formed by self-organisation in a bottom-up process. This is demonstrated for the deposition of the transition metals Fe, Co and Ni which, on the flat (1 0 0) surface, would be under considerable tensile strain of the order of 8–9%. We show that the accompanying stress leads to the formation of stair-rod dislocations by which the stress is relaxed. Calculations using density functional theory (DFT) reveal for the ( 1 × 1 ) phase as substrate that these dislocations appear at a coverage of about 3–4 monolayers and are either pinned by surface defects or by further adatoms which decorate them. On the (5 × 1)-H phase this pinning appears with long-range order. So, by the Ir wires at the interface the developing nanostructures including the dislocations can be structurally accessed by experiment, here with crystallographic precision by quantitative low-energy electron diffraction (LEED). Moreover, scanning tunneling microscopy (STM) reveals both the morphology of the nanostructured films and their buckling with atomic resolution.