Far Infrared Spectroscopy of Ultra-Thin Films.

This dissertation describes the development of a double polarization modulation technique, which allows for high far-infrared sensitivity to dielectric films deposited on metallized substrates. This new spectroscopy is based on the polarization specificity of the grazing angle reflectance of a thin dielectric coating on a conducting surface. The design is a modification of a Martin-Puplett configuration Michelson interferometer. The reflection absorption (RA) process has been computer modeled. Based on this model, far-infrared RA spectroscopy is compared to both mid-infrared RA spectroscopy and to standard normal transmission experiments. Physical arguments are presented to explain the differences between them in terms of macroscopic fields and the classical oscillator model of the dielectric function. The computer model allows for spectral line fitting and a method for fitting RA spectra is discussed. Far-infrared spectra and analysis are performed for two different thin film systems. The first system is a highly ionic thin film sample of potassium iodide (KI). Through fits to the KI thin film spectra, the effect of two phonon processes on the bulk LO mode of the KI crystal is discussed along with possible surface effects in the very thin samples. The second thin film system is the polymer Poly-Ethylene Oxide (PEO). The far-infrared spectra obtained from these polymer films is shown to be related to the high degree of crystallinity obtainable in the thin polymer film.