Self‐assembled monolayers of 4‐aminothiophenol on copper surfaces studied by grazing‐incidence X‐ray absorption spectroscopy

Self-Assembled Monolayers (SAMs) of 4-Aminothiophenol on copper surfaces have been investigated, using Grazing Incidence X-Ray Absorption Spectroscopy (GIXAS). The surface sensitivity of this technique allows us to characterize the chemisorption process by XANES and EXAFS measurements in fluorescence mode at the sulfurand copper-K-edge. Our results are consistent with 4-Aminothiophenol (4-ATP) bound to the surface through the sulfur headgroup. From EXAFS analysis two different interatomic distances between sulfur and next neighbour copper atoms ds-c~,l = 2.26/~ and ds-c~,2 = 3.1/~, could be determined. Data indicates occupation of deep three-fold hollow positions of sulfur with significant reconstruction of first layer copper atoms on preferably textured (11 l)-surfaces. Adsorption of 4-ATP as disulfide, described in a "sulfur-pairing model", is not supported by absorption data in the XANES region. EXAFS analysis on the other hand gives some evidence for the presence of a sulfur dimer moiety, with a sulfur-sulfur spacing of d s s = 2.1 /~,. Depefiding on the preparation procedure, oxidation of thiol-molecules occurs, leading to a coexistence of sulfate-ions and intact 4-ATP on metal surfaces due to partial cleavage of the S-C bond.