LEEDI–Vand DFT structure determination of the (\surd 3\times \surd 3)\mathrm {R}30^{\circ } Pb–Ag(111) surface alloy

Abstract

The deposition of 1/3 of a monolayer of Pb on Ag(111) leads to the formation of PbAg(2) surface alloy with a long range ordered (√3 × √3)R30° 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 PbAg(2) surface alloy, as expected, with the Pb atoms residing approximately 0.4 Å above the Ag atoms due to their size difference. DFT calculations are in good agreement with the LEED results.

Substrate-mediated umklapp scattering at the incommensurate interface of a monatomic alloy layer

“…The radius of Pb, Ge, and, Ag atoms are 1.8, 1.25, and 1.6 Å, respectively [32], so upon the Ag 2 Pb alloy formation, a Pb atom, due to its larger size, can only be partially immersed into the top Ag layer until the alloy lattice is commensurate with AgÝ3-R30. This is consistent with a previous LEED IV study showing that the top layer is corrugated such that the Pb atoms reside about 0.4 Å above the Ag atoms [33]. However, for a Ge atom, due to its much smaller size, the lattice of Ag 2 Ge further contracts to a smaller value than that of AgÝ3-R30.…”

Bidimensional phases in Co–Pt surface alloys: A theoretical study of ordering and surface segregation

“…3)R30(111) has also been observed on immiscible systems like Bi/Cu(111) [54,55], Bi/Ag(111) [56], Pb/Ni (111) [57] and Pb/Ag(111) [58][59][60]. In theory, we already obtained this surface chemical ordering on the (111) facets of Pd-Au nanoalloys [61], which was never pointed out before on nanoalloys.…”

“…3)R30 surface structure is a 2D chemical ordering which has no relation with the underlying bulk alloy and has been seen by atom deposition in ultra-vacuum conditions on pure metal surfaces in systems like Sn on Pt(111) [50,51,[78][79][80], Sb on Cu(111) and Ag (111) [81], Bi on Cu(111) [54,55] or Ag(111) [56], Te on Cu(111) [53], Sn on Ni(111) [52], and Pb on Ni(111) [57] or Ag(111) [58][59][60]. It has also been obtained from surface segregation of solid solutions of Sn or Al in copper-based alloys single crystal surfaces: α-Cu .95 Sn .05 (111) [47] and α-Cu .84 Al .16 (111) [48,49].…”

Simple Model for Corrugation in Surface Alloys Based on First-Principles Calculations

“…There were not so many experimental and theoretical studies for the corrugations in M /Ag (111); we only obtained values of corrugation parameters for M = Ge, Pb, and Bi [ 9 , 14 , 21 , 22 , 23 , 24 ]. The calculated corrugations of Pb and Bi are comparable to the experimental results at finite temperature [ 9 , 22 ] and other calculations [ 9 , 14 , 22 , 23 , 24 ], while for M = Ge, we obtain a result of −0.05 Å different from the experimental value of 0.3 Å [ 21 ].…”