Characterization of thiolate-based mono- and bilayers by vibrational spectroscopy: A review

In this review, the use of vibrational spectroscopy to probe the structure and organization of thin organic layers adsorbed onto metal surfaces is discussed. This review concentrates on thiolate-based mono- and bilayers. Many different techniques have been applied to characterize such organic systems. Those based on vibrational spectroscopy are reviewed in this paper, that is: infrared absorption (including SEIRA: surface-enhanced infrared absorption), Raman scattering (including SERS: surface-enhanced Raman scattering), vibrationally resonant sum frequency generation (SFG) and high-resolution electron energy loss spectroscopy (HREELS). Surface vibrational spectroscopies are preferentially sensitive to selected vibrations of certain moieties, e.g. moieties in the close proximity of the metal surface (SERS, SEIRA), at the outermost part of the film (off-specular HREELS) or vibrations of electronic chromophores (resonance Raman). This review is an attempt to provide an overview of the structural information that can be obtained from various surface vibrational techniques for thiolate-based mono- and bilayer systems. Experimental limitations of the different techniques are also discussed.