Ir reflectance properties of weakly and strongly absorbing surface films

In an external reflection measurement, the optical properties of a surface film can give rise to a variety of spectral behavior on metallic and nonmetallic substrates. The diversity of behavior can be explained by the presence of transverse optical (TO) and longitudinal optical (LO) bands of the film in the infrared region. The excitation modes associated with these bands are directional with respect to the plane of the surface. Spectral interpretation is facilitated by understanding the roles of the TO and LO bands in reflectance spectra, the substrate selection rules for the appearance of these bands, and the relationship between the TO and LO frequencies. We will show that weakly absorbing films have a simpler optical behavior than strongly absorbing films. © 1989, SPIE.