Total internal reflection Raman spectroscopy

Abstract

Feasibility of total internal reflection (TIR) Raman spectroscopy as a new tool for characterizing thin surface layers has been investigated, starting with selection of the material for the internal reflection element (IRE). Sapphire was found to be the most suitable for the IRE among TiO2, SrTiO3, several kinds of flint glasses, and sapphire itself. The potential of TIR Raman method was proved by measurements on the two-layered samples consisting of a thin surface layer of polystryene and a base layer of polyethylene. The thickness of the surface layer that could be measured by the present technique was then extensively investigated for the two-layered samples which had the surface layer of polystryrene varying in thickness (0.006–0.93 μm) and the base layer of a constant thickness of polycarbonate (12 μm). We could measure vibrational spectra of the surface layers as thin as 0.006–0.2 μm sufficiently separately from those of the base layer. Thickness of the measurable surface layer could be varied to a great extent by changing the incident angle. The observed results were in good agreement with what was deduced from the nature of the evanescent wave.