The infrared properties of most oxide films are dominated by the effects of the lattice vibrations which
are well represented by a model of superposed classical oscillators. In this model, the complex
dielectric constant is a function of one or more classical oscillators hosted in a dielectric medium. Each
oscillator is specified by its strength, resonance wavelength, and linewidth or damping.
Evaluation of the oscillator parameters takes advantage of the observation by Berreman that a thin film
has a strong absorption band for p-polarized light at oblique incidence at the wavelength for which the
dielectric constant is zero or nearly zero. Each absorption band corresponds to a lattice vibration band
which is represented by an oscillator.
The p-polarized transmittance at 45° incidence of 0. 1 micron thick films of iron oxide, silicon oxide and
silicon nitride was measured. These data were fitted with dispersion models composed of superposed
classical oscillators. The results indicate that the properties of silicon oxide and iron oxide films are each
modelled by three classical oscillators hosted in a pure dielectric medium. Similarly, the silicon nitride
results are represented by two oscillators.
Joseph H. Apfel,
"Classical oscillator dispersion model for optical coatings", Proc. SPIE 1270, Optical Thin Films and Applications, (1 August 1990); doi: 10.1117/12.20368; https://doi.org/10.1117/12.20368