Initial growth of Cu on Ir(100)-(5 x 1)

The structure of the clean and Cu covered Ir(100)-(5 x 1) surface has been studied with scanning tunneling microscopy and spectroscopy (STM/STS), low energy electron diffraction (LEED) and ion scattering spectroscopy (ISS). S TRI images of the reconstructed Ir surface with atomic resolution directly reveal a two-bridge registry configuration of the quasi-hexagonal layer. Gr owth of Cu starts with the formation of strongly anisotropic islands induce d by the lateral asymmetry of the (5 x 1) reconstruction. The Cu island for mation is accompanied by direct lifting of the Ir reconstruction. The lifti ng process is not limited to the area beneath the islands but continues ont o the Ir terraces. Two-dimensional layer growth occurs at room temperature for a coverage below 0.6 ML. Upon annealing, the anisotropic Cu areas coale sce into larger islands of laterally more compact shape. The excess Ir atom s originating from the lifted reconstruction create a well-separated two-di mensional Ir phase inside the Cu islands. STS local barrier-height measurem ents exhibit strong chemical contrast between Cu and Ir areas. Phase separa tion between Ir and Cu is visible in the entire investigated coverage and t emperature range, neither intermixing nor segregation has been found. (C) 2 000 Elsevier Science B.V. All rights reserved.