LEED I–V and DFT structure determination of the Pb–Ag(111) surface alloy

The deposition of 1/3 of a monolayer of Pb on Ag(111) leads to the formation of PbAg2 surface alloy with a long range ordered superstructure. A detailed analysis of this structure using low-energy electron diffraction (LEED) I–V measurements together with density functional theory (DFT) calculations is presented. We find strong correlation between experimental and calculated LEED I–V data, with the fit between the two data sets having a Pendry's reliability factor of 0.21. The Pb atom is found to replace one top layer Ag atom in each unit cell, forming a substitutional PbAg2 surface alloy, as expected, with the Pb atoms residing approximately 0.4 A above the Ag atoms due to their size difference. DFT calculations are in good agreement with the LEED results.