Subsurface Layer Studies by Attenuated Total Reflection Fourier Transform Spectroscopy

In total reflection spectroscopy the effective sampled depth increases as the angle of incidence approaches the critical one. At each angle of incidence, successive layers within the sample are weighed differently in the overall spectrum, and the manner of this weighing changes with angle. It is thus possible in principle to deconvolute a set of spectra taken at different angles into spectra corresponding to successive depth invervals. As this angular effect is particularly marked near the critical angle, where attenuated total reflection spectra are severely distorted, the spectra usually require inversion into optical constant spectra. This has been done by a new technique that measures spectra twice at each angle with different prism materials to give the necessary data sets. Examples of such subsurface spectra are shown.