Density Functional Theory Study of the Adsorption of Alkanethiols on Cu(111), Ag(111), and Au(111) in the Low and High Coverage Regimes

Abstract

The structure, the surface bonding, and the energetics of alkanethiols adsorbed on Cu(111), Ag(111), and Au(111) surfaces were studied under low and high coverages. The potential energy surfaces (PES) for the thiol/metal interaction were investigated in the absence and presence of externally applied electric fields in order to simulate the effect of the electrode potential on the surface bonding. The electric field affects the corrugation of the PES which decreases for negative fields and increases for positive fields. In the structural investigation, we considered the relaxation of the adsorbate and the surface. The highest relaxation in a direction perpendicular to the surface was observed for gold atoms, whereas silver atoms presented the highest relaxation in a plane parallel to the surface. The surface relaxation is more important in the low coverage limit. The surface bonding was investigated by means of the total and projected density of states analysis. The highest ionic character was observed on the copper surface whereas the highest covalent character occurs on gold. This leads to a strong dependence of the PES with the tilt angle of the adsorbate on Au(111) whereas this dependence is less pronounced on the other metals. Thus, the adsorbate-relaxation and the metal-relaxation contributions to the binding energy are more important on gold. The adsorption of thiols on gold was investigated on the 111 surface as well as on a surface with gold adatoms in order to elucidate the effect of thiols on the surface diffusion of gold. The CH(3)CH(2)S radical adsorbs ontop of the gold adatom. The diffusional barrier of the CH(3)CH(2)SAu species is lower than that for a bare gold adatom and is also lower than that for the bare thiol radical. The adsorption of the molecular species CH(3)SH and CH(3)CH(2)SH was also investigated on Au(111). They adsorb via the sulfur atom ontop of a gold atom. On the other hand, the adsorption of the alkanethiol radicals on the perfect 111 surfaces occurs on the face centered cubic (fcc)-bridge site in the low coverage limit for all metals and shifts toward the fcc site at high coverage on copper and silver.

The interface structure of n-alkylthiolate self-assembled monolayers on coinage metal surfaces

“…Cometto et al [67]; interestingly, these authors also found that the total energy of this Au-adatom-thiolate moiety was also most identical in the fcc and hcp hollow sites, and that the barrier to diffusion between these sites is very low, consistent with facile diffusion at room temperature between these sites. This result provides a rationale for the facile interchange of the (√3x√3) At this point it is appropriate to summarise the main conclusions regarding the simplest system, Au(111)/methylthiolate, which has been investigated in detail only at low coverage (by STM) and in the 0.33 ML ordered (√3x√3), phase as described above.…”

Electric Field-induced Charge Transfer of (Bu4N)2[Ru(dcbpyH)2-(NCS)2] on Gold, Silver, and Copper Electrode Surfaces Investigated by Means of Surface-enhanced Raman Scattering

“…[20][21][22][23][24][25][26][27] Recently a density functional theory study was performed to investigate the adsorption of alkanethiols on Cu, Ag, and Au surfaces, predicting dissimilar ionic characteristics depending on the metal substrates. 28 Solvent dependent charge transfer of the ruthenium bipyridine (Ru-bpy) dye on colloidal Ag and Au surface has been recently reported by means of SERS. 29 Although quite a few studies have explored the different adsorption structures of SAMs on metal surfaces, [20][21][22][23][24][25][26][27][28] no reports have investigated ruthenium bipyridine (Ru-bpy) dye on metal surfaces using potential dependent vibrational spectroscopy.…”

Photoemission core-level shifts reveal the thiolate-Au(111) interface

“…The relative stabilities suggest that the interface consists of MeS-Au-MeS complexes. Several alternative structures have been proposed during recent years [15][16][17][18][19] of which some are preferred over the traditional model but not over the structure with methyl thiolate complexes ͓Fig.…”

“…[9][10][11][12][13][14] This configuration is, however, predicted to be unstable with respect to surface reconstruction with RS adsorbed at defects 15,16 or adatoms. [17][18][19][20][21] Among the different suggestions, one that comprises two RS-Au-RS units in each c͑4 ϫ 2͒ supercell is predicted to be energetically favored. 22 Although there is an uncertainty concerning the ability of state-of-the-art DFT methods to predict small energy differences ͓in particular, for reconstructed RS / Au͑111͒ systems, as the cohesive energy of gold is underestimated by ϳ15%͔ the structure based on RS-Au-RS units is consistent with the bulk of experimental data.…”