Growth of thin Sn films on Ag(111)studied with low-energy electron diffraction and X-ray photoelectron spectroscopy

Thin Sn films on Ag(111)grown at different Sn coverage and substrate temperature were characterized with low-energy electron diffraction and x-ray photoelectron spectra. The results show that surface alloying of Sn atoms on Ag(111)occurs at a temperature as low as 96 K, indicating a strong tendency to form a surface alloy between Sn and Ag. During the alloying, Sn atoms substitute Ag atoms in random locations, resulting in a disordered Sn/Ag(111)surface. The alloy surface becomes completely ordered with a (√3 × √3)R30° reconstruction (the √3 phase)only when it is annealed above 453 K, but annealing at 403 K converts all Sn atoms on Ag(111)into the alloy state; the surface coverage of Sn is no more than 1/3 monolayer with excess Sn diffusing into the Ag(111)substrate. These observations indicate that the √3 phase with the Sn-Ag surface alloy is the only ordered phase obtainable on Sn/Ag(111)once the Sn-Ag surface alloy is formed. It is consequently impracticable to grow non-alloy ordered phases, such as stanene, on Ag(111)epitaxially at a temperature above 96 K, showing evident discrepancies with the conclusions of the previous computational study.