INFRARED REFLECTION STUDIES OF CERAMICS - CHARACTERIZATION OF SIC LAYERS ON GRAPHITE SUBSTRATES

Technical CVD-grown silicon carbide (beta-SiC) layers on graphite substrates have been studied by infrared spectroscopy. Specular reflectance spectra were measured at oblique incidence, and for the same experimental conditions such spectra were simulated starting from oscillator parameters which basically determine the optical behaviour of the material. Both the roughness of the surface and the roughness of the interface within the coated material, have considerable influence on the spectra. Modelling these zones as gradient layers on the basis of effective-medium approximations, convincing agreement between experiment and simulation can be obtained. In this way the effective dielectric function of the layer, as well as its thickness, are derived. Certain features within the reststrahlen band can be assigned to the excitation of surface phonons which strongly depend on the morphology of the layer.