Raman Spectroscopy of Thin Organic Films by Integrated Optical Techniques

Abstract

Vibrational spectroscopy of molecules at the surfaces of thin films has become increasingly important for surface studies. Enhancement mechanisms are however needed to improve the signal to noise ratio in order to observe these surface molecules. To this end integrated optical techniques have been utilized to measure the resonant and nonresonant Raman spectra of some organic molecules in thin films ranging in thickness from 3 to 80 nm. These films were deposited on glass optical waveguides and laser radiation was coupled into the layered structure by prism coupling techniques. The streak of light in the waveguide was focused onto the slit of a JY RAMANOR HG-2S double monochromator to collect the Raman scattered light. The increased optical intensity and scattering volume (the optical ray makes the order of a thousand reflections) enabled us to obtain high S/N spectra, therefore making this technique very generally applicable to the study of organic and polymeric thin films. Our non-resonant Raman results on thin films of poly(styrene) and our resonant Raman results on a Langmuir-Blodgett monolayer of squarylium and cyanine dyes will be presented as well as details of the method.