Initial growth of Cu on Ir(100)-(5×1)

The structure of the clean and Cu covered Ir(100)-(5×1) surface has been studied with scanning tunneling microscopy and spectroscopy (STM/STS), low energy electron diffraction (LEED) and ion scattering spectroscopy (ISS). STM images of the reconstructed Ir surface with atomic resolution directly reveal a two-bridge registry configuration of the quasi-hexagonal layer. Growth of Cu starts with the formation of strongly anisotropic islands induced by the lateral asymmetry of the (5×1) reconstruction. The Cu island formation is accompanied by direct lifting of the Ir reconstruction. The lifting process is not limited to the area beneath the islands but continues onto the Ir terraces. Two-dimensional layer growth occurs at room temperature for a coverage below 0.6 ML. Upon annealing, the anisotropic Cu areas coalesce into larger islands of laterally more compact shape. The excess Ir atoms originating from the lifted reconstruction create a well-separated two-dimensional Ir phase inside the Cu islands. STS local barrier-height measurements exhibit strong chemical contrast between Cu and Ir areas. Phase separation between Ir and Cu is visible in the entire investigated coverage and temperature range; neither intermixing nor segregation has been found.