Generalized Two-Dimensional Fourier Transform Infrared Multiple-Angle Attenuated Total Reflection Spectral Depth-Profiling Analysis of Multilayer Samples

Abstract

This paper reports the application of a generalized two-dimensional (G2D) correlation method in multiple-angle single-reflection attenuated total reflection (ATR) spectral depth-profiling analysis of multilayer samples. In this method, ATR spectra at different incident angles are used to generate two-dimensional (2D) correlation spectra. The relative spatial interactions of correlated signals are then determined from the signs of the corresponding contours of the asynchronous map. In order to apply this method to multilayer samples, effects of dispersion in refractive indices of materials which create pseudo-contours were first investigated with simulated ATR spectra. Model ATR spectra were generated from conventional antisymmetric linear combinations of the Lorentzian functions. The use of Ge ATR crystals minimizes the pseudo-contours and allows the method to be successfully applied to actual multilayer samples. A 0.1 μm thick gelatin layer on a polyester film and a 0.2 μm thick polycarbonate layer on the gelatin/polyester film were investigated as actual model samples. In the model samples, although the layers were thin, the relative depth of each layer was easily determined.