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

Technical CVD-grown silicon carbide (beta-SiC) layers on graphite subs trates have been studied by infrared spectroscopy. Specular reflectanc e spectra were measured at oblique incidence, and for the same experim ental conditions such spectra were simulated starting from oscillator parameters which basically determine the optical behaviour of the mate rial. Both the roughness of the surface and the roughness of the inter face within the coated material, have considerable influence on the sp ectra. Modelling these zones as gradient layers on the basis of effect ive-medium approximations, convincing agreement between experiment and simulation can be obtained. In this way the effective dielectric func tion of the layer, as well as its thickness, are derived. Certain feat ures within the reststrahlen band can be assigned to the excitation of surface phonons which strongly depend on the morphology of the layer.