Strained Pd films, by epitaxial growth on Au(1 1 0), to control catalytic properties

Pd ultra thin films on Au(1 1 0)-(1×2) have been prepared at 300 K by vapour deposition and studied using medium energy electron diffraction (MEED), surface X-ray diffraction (SXRD), low energy electron diffraction, low energy ion scattering (LEIS) and Auger electron spectroscopy (AES). The (1×2) superstructure intensities are strongly attenuated during the deposition of the first 0.5 ML. Simultaneously, LEIS indicates that gold atoms cover a large fraction of the deposited Pd atoms. A quantitative SXRD analysis of the 0.5 ML Pd film reveals a significantly ordered interface alloy covered by two incomplete Au layers. When more Pd is deposited up to about three layers, the growth proceeds in a quasi layer by layer mode, while the surfactant effect of gold persists. In this range of thickness, the film, mainly composed of Pd atoms, is under tensile strain in coherent epitaxy with the Au(1 1 0) substrate.