Adsorption and Dissociation of R-Methyl p-Tolyl Sulfoxide on Au(111)

Sulfur-based molecules producing self-assembled monolayers on gold surfaces have long since become relevant functional molecular materials with many applications in biosensing, electronics, and nanotechnology. Among the various sulfur-containing molecules, the possibility to anchor a chiral sulfoxide to a metal surface has been scarcely investigated, despite this class of molecules being of great importance as ligands and catalysts. In this work, (R)-(+)-methyl p-tolyl sulfoxide was deposited on Au(111) and investigated by means of photoelectron spectroscopy and density functional theory calculations. The interaction with Au(111) leads to a partial dissociation of the adsorbate due to S-CH₃ bond cleavage. The observed kinetics support the hypotheses that (R)-(+)-methyl p-tolyl sulfoxide adsorbs on Au(111) in two different adsorption arrangements endowed with different adsorption and reaction activation energies. The kinetic parameters related to the adsorption/desorption and reaction of the molecule on the Au(111) surface have been estimated.

Density functional theory simulation of the adsorption of sulphur multilayers on Au(100)

The adsorption of sulphur multilayers on Au(100) has been studied using density functional theory (DFT) within the generalized gradient approximation (GGA). The first sulphur layer was adsorbed on the four-fold sites of the unreconstructed Au(100) surface forming a lattice. The experimental parameters of the lattice were reproduced taking into account the surface expansion of the topmost Au(100) layer. This expansion should occur when gold islands are formed after the lifting of hex-reconstruction, which allows the lateral movement of the gold atoms. The second sulphur layer, on top of the lattice, consisted of eight S atoms (octomer phase) in a quasi-rectangular arrangement. The structural optimization of the octomer phase was achieved in a specific spatial orientation with respect to the lattice. The analysis of Bader atomic charges and the projected density of states (PDOS) demonstrated that charge transfer from the Au(100) surface to the sulphur layers, sulphur chemisorption and sulphur-sulphur inter-layer mixing of electronic states control the formation of sulphur multilayers.