Ellipsometry and reflection, luminescence and Raman spectroscopies of monolayer assemblies on solid substrates

Abstract

Long-chain fatty acid monolayer assembles were built up on metal and semiconductor surfaces by the Langmuir-Blodgett dipping technique. Ellipsometry was used to characterize the multilayers. At the air-metal interface of silver gratings, plasmon surface polaritons (PSPs) can be excited directly. The dispersion of the PSP modes and its dependence on the overcoatings was determined by reflection and luminescence measurements. The high field of the PSP was used to enhance the Raman spectra of cadmium arachidate layers. It is shown how the different spectral regions are individually enhanced by selecting the appropriate scattering angle. The dependence on film thickness of the intensities of the Raman vibrational bands and the PSP dispersion parameters such as the position and width of the gap at the Brillouin zone centre are presented. Raman peak intensity ratios can be used to evaluate an order parameter for the different layers. It is shown that this parameter decreases with increasing layer thickness. If dye layers are intercalated into the monolayer assembly, weak flourescence from the dye can be detected. In addition, emmission of light occurs from all the PSP modes of energy lower than that of the exciting light. Thi emmission is identified by its characteristic polarization and the dependence of its wavelength on the angle of emission. At energies within the absorption bands of the dye monolayer, this emission is greatly enhanced.