Infrared Spectroscopic Ellipsometry of Self-Assembled Monolayers
Curtis W. Meuse
Ellipsometry measures the relative intensity of and the phase difference between the parallel (p) and perpendicular (s) components of an electric field vector interacting with a sample. In this paper, a technique using polarized Fourier transform infrared spectroscopy (FTIR) for measuring this information, as the complex optical density function, is presented. The advantage of the complex optical density function is that it relates the changes in the polarization state to an uncoated reference sample instead of to the plane of incidence. This simplifies the calibration procedure and clarifies what is being measured since the specific properties of the metal surface and experimental setup are removed from the results. In this configuration, the precise positioning of the sample compared to the reference surface and the reproducibility of the analyzer movement are the most important contributions to the error in the complex optical density function. In this paper, we demonstrate that these errors are small compared to the changes from the presence of a self-assembled monolayer. We then compare the measured complex optical density functions to ones simulated using electromagnetic wave theory models for measured complex optical density functions to ones simulated using electromagnetic wave theory models for describing the optical properties of multilayer samples. By matching our measurments and simulations, we are able to determine the molecular orientations of the alkane bhains and the thicknesses of the monolayers.