X-ray photoelectron spectroscopy study of thiols adsorbed on Pt(111) with and without the presence of a copper monolayer

The displacement of an electrodeposited Cu monolayer on Pt(111) single crystal by 2-mercaptopyridine (2-MP) and 4-mercaptopyridine (4-MP) has been investigated by XPS. The results indicate that the Cu adatoms are partially displaced by the 4-MP and completely displaced by the 2-MP, An analysis of the S 2p spectra of 2-MP and 4-MP adsorbed on Pt(111) both with and without the presence of a Cu monolayer reveals a small binding energy shift between 2-MP and 4-MP emissions. This effect is probably due to the formation of a surface chelate for 2-MP via bonding through both nitrogen and sulphur atoms. An additional component is assigned to sulphur atoms in dimers, and its intensity correlates with that of the N-Pt component in the N 1s spectra, suggesting that N-Pt interaction decreases the dimer formation probability. In the case of the presence of the Cu adlayer on Pt(111) before mercaptopyridine adsorption, the N-Pt interaction decreases and thus favours dimerization, The presence of sulphates on the surface after the displacement reaction could originate in part from oxidation of the reduced mercaptopyridine. Copyright (C) 2000 John Wiley & Sons, Ltd.