LEED and photoemission study of growth and structural evolution of Sn on Ag(001)

Growth of tin (Sn) on Ag(001) substrate has been studied at elevated temperatures using low energy electron diffraction (LEED), x-ray photoemission spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) measurements. A c(2 × 2) ordered surface is observed for very low coverages (0.1 ML) of Sn which subsequently transforms into a p(2 × 2) ordered surface for 0.25 ML Sn coverage, suggesting formation of a substitutionally ordered surface alloy. For higher coverages of Sn beyond 0.5 ML, no further structural evolution was observed with a constant p(1 × 1) LEED pattern. Our XPS results indicate diffusion of Ag atoms into Sn layers and forming Ag-Sn alloy film. Along with LEED and XPS, our ARPES results confirm the presence of an ordered Ag overlayer on the alloy film, suggesting a sandwich structure. Our studies are important in understanding the growth mechanism and electronic properties of Sn films on noble metal substrates.