EXPERIMENTAL ASPECTS OF ATTENUATED TOTAL REFLECTANCE SPECTROSCOPY IN THE INFRARED

It is well known that attenuated total reflectance (ATR) infrared spec troscopy is a very sensitive technique for the investigation of thin f ilms. In this paper it is shown that additional internal reflection me asurements below the critical angle are generally necessary for a quan titative interpretation of the ATR spectra. In the case of very thin l ayers configurations are found which are very sensitive on undesired r esidual vacuum gaps in the 10-nm range between a solid sample and the ATR prism. On the other hand, in experiments where surface polaritons are excited a coupling gap with a thickness on the order of 100-1000 n m is necessary between sample and prism (Otto geometry). The thickness of this layer can be obtained by evaluating the Fabry-Perot interfere nces which occur inside the coupling gap if the angle of incidence is below the critical angle.