OPTICAL-PROPERTIES OF METAL-SURFACES FROM ELECTRON-ENERGY LOSS SPECTROSCOPY IN THE REFLECTION MODE

The development and evaluation of a method to determine optical constants using electron energy loss spectroscopy (EELS) in the reflection mode is reported. An empirical approach is taken in these studies in order to minimize the necessity for a-priori information concerning the sample of interest. The goal of this research is to determine optical constants of metal systems using a standard electron spectrometer and very little sample preparation. The data treatment involves isolating the loss function from the experimental EEL spectrum by (a) deconvolution of the surface plasmon contribution from the data obtained with a high-energy primary beam using data acquired with a low-energy primary beam at a grazing incidence angle, (b) minimization of the plural scattering contribution through deconvolution of a model spectrum obtained experimentally, and (c) removal of the dispersion contribution through deconvolution of a theoretical dispersion function. The complex dielectric function is obtained through a Kramers-Kronig analysis of the isolated loss function. The results for Al acquired with several primary beam energies are presented and compared to literature values. These results indicate that the proposed method is most successful for determining the dielectric function of Al when primary beam energies of 1500 eV or greater are employed. The results also suggest that dispersion effects can be minimized experimentally using primary beams of relatively high energy. © 1990.