Ordered surface alloy formation of immiscible metals: The case of Pb deposited on Ag(111)

Abstract

The deposition of $1∕3$ Pb monolayer at room temperature onto Ag(111) leads to a $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ superstructure. We present here a detailed structural study of this surface structure by synchrotron radiation surface x ray diffraction (SR-SXRD) and scanning tunnel microscopy (STM). We show that Pb atoms are embedded into the silver top surface layer forming an ordered ${\mathrm{Ag}}_{2}\mathrm{Pb}$ surface alloy despite the strong tendency of the system to phase separate in the bulk. Quenched molecular dynamics simulations allow us to interpret this ordering reversal, in terms of size-mismatch induced surface alloying.