Intermixing and subsurface alloy formation: Ir on Cu(100)

The growth and structure of Ir films on Cu(100) up to 1.5 ML have been inve stigated by means of scanning tunneling microscopy (STM), low-energy ion sc attering spectroscopy (ISS), X-ray photoelectron spectroscopy (XPS) and low -energy electron diffraction (LEED). After Ir deposition at 200 K strong in termixing of Cu and Ir has been found, giving rise to step roughening and s urface etching. With the help of ISS the amount of Ir in the first layer wa s determined to be less than 20% of the nominal Ir coverage. Temperature-de pendent ISS and XPS measurements indicate that, upon annealing, Ir first se gregates completely into the subsurface layer and finally, for temperatures above 650 K, into deeper layers. In the STM images the Ir atoms in the sec ond layer are visible owing to a chemical contrast. Deposition of Ir at 620 K results in the formation of a long-range ordered subsurface alloy. The L EED pattern exhibit a (2 x 1) superstructure with maximal intensity of the half-order spots occurring at an Ir coverage of about 0.5 ML. In the STM im ages the surface is marked by a chain-like structure, with chains running a long the [011] directions. The measured corrugation of 0.3 Angstrom in STM appeared due to imaging the electronic differences of the embedded Ir-Cu al loy layer. The ordered alloy phase can be modeled by alternating Cu and Ir chains located in the second layer that are covered completely by one coppe r layer. (C) 1999 Elsevier Science B.V. All rights reserved.