Self-assembled multilayers of 4,4′-dimercaptobiphenyl formed by Cu(II)-catalyzed oxidation

Self-assembled multilayers were prepared by alternate deposition of 4,4'-dimercaptobiphenyl (DMBP) and copper(II) ions onto planar Au(111) substrates. The multilayers were characterized by ellipsometry, external reflectance Fourier transform infrared spectroscopy (ER-FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Ellipsometry and ER-FTIR results show a linear relationship between the number of layers and the integral area of absorption, characteristic of vibrational modes assigned to the biphenyl moieties. XPS data suggest that the copper is present in the +1 and +2 oxidation states in bulk material made by the reaction of DMBP and Cu(II) ions in solution, and only in the +1 state in multilayer films. XPS results also indicate a linear relationship between the number of DMBP layers and film thickness. AFM studies provided details about the surface morphology. In addition, thickness was measured precisely via nanoshaving and nanografting techniques. On the basis of the combination of these techniques, it is proposed that the DMBP multilayer system is formed by interlayer disulfide linkages.