STABILIZATION OF CO PT(111) AGAINST SURFACE ALLOYING BY AG OVERLAYERS/

The initial growth and annealing effects of Ag ultrathin films on the surface of 1 ML Co/Pt(lll) were investigated by low-energy electron di ffraction (LEED), Auger electron spectroscopy, and ultraviolet photoel ectron spectroscopy. The Ag atoms are in a layer-by-layer growth only of the first two atomic layers. Within these coverages, the adatoms of Ag are in instability when the substrate starts Co-Pt alloying. The i ntensity of the specular beam of LEED versus temperature increases dra matically after the alloy formation is complete. The temperature of th e formation of the Co-Pt alloy becomes higher as the coverage of Ag in creases. These unusual phenomena are, to our knowledge, the first obse rvation in the systems containing three-component ultrathin films. The stress of overlayers causing the change of the alloying temperature i s proposed.