A SEARCH FOR CLOCK RECONSTRUCTION IN FCC (001) SURFACES INDUCED BY MONOLAYER METAL-FILMS - PD CU(001), PT/CU(001) AND PD/PT/CU(001)/

Low energy ion scattering (LEIS) and low energy electron diffraction ( LEED) have been employed to investigate the Pd/Cu(0 0 1), Pt/Cu(0 0 1) and Pd/Pt/Cu(0 0 1) systems. A monolayer of Pd deposition on a Cu(0 0 1) surface at room temperature (RT) induced a (2 x 2) p4g clock recon struction. We present evidence that this reconstructed phase correspon ds to a model of similar to 20% pure Pd islands above an ordered c (2 x 2) substrate, which is mixed with c (2 x 2) Cu-Pd regions. The later al displacement of surface island Pd atoms was measured to be 0.25 +/- 0.07 Angstrom through comparisons with 3D computer simulation. For 1 ML Pt on Cu(0 0 1) at RT, however, an ordered c (2 x 2) structure form ed only after annealing to 150-200 degrees C. No reconstruction was ev idenced. Two simple rules for governing the occurrence of the clock re construction are proposed. In order to learn whether the size differen ce between Pd and Cu in an ordered (2 x 2) substrate has a strong infl uence and acts as a template for the reconstruction, we have also stud ied the Pd/Pt/Cu(0 0 1) system. Evidence for the p4g clock reconstruct ion was found by deposition of 0.5 ML Pd above an ordered c (2 x 2) Cu -Pt substrate. Copyright (C) 1996 Elsevier Science Ltd