Self-Assembled Monolayer Induced Au(111) and Ag(111) Reconstructions: Work Functions and Interface Dipole Formation

Adsorption of self-assembled monolayers (SAMs) on metal surfaces leads to interface dipole layers that strongly modify the metal work functions. Recently, alkanethiolate SAMs have been shown to give rise to substantial reconstructions of the Au(111) and Ag(111) surfaces. In this paper, we study by means of first-principles calculations how such reconstructed alkanethiolate SAMs on Au and Ag interfaces modify the interface dipole layer and the work function. The impact of SAM-induced reconstructions is remarkably moderate in the Au case, giving rise to work function changes of ≲0.25 eV as compared to the unreconstructed case. Neither the Au work function is altered much by reconstructions nor the orientation of the molecular dipoles in the SAMs. In contrast, in the Ag case, a SAM-induced reconstruction alters the work function by ≳0.4 eV. The different behavior of Au and Ag substrates is partly explained by the participation of the Au 5d states in the surface electronic structure, moderating the impact of a reconstruction, whereas there is no such participation of the Ag 4d states.