Special substrate-film designs are used to measure roughness-induced scattering and scattering from the volume of optical thin films separately. So theoretical models of surface roughness and volume scattering become applicable to the experimental data, and quantitative information on thin-film microstructure can be derived. Measuring total integrated and angle-resolved scattering on oxide, fluoride, and chalcogenide films of different film thicknesses yields the evolution law of microstructural growth, which for the majority of investigated films roughly follows a square-root dependence on film thickness. Packing densities of fluoride films calculated from volume-scattering data are found to agree with results from quartz-crystal monitoring.

No abstract

No abstract

A theoretical model is presented that describes the volume scattering in thin optical films, particularly in typical columnar structures. It is based on a first-order perturbation theory that concerns the fluctuation of the dielectric permittivity in the film. For evaporated PbF(2) films that show a pronounced columnar morphology, angular as well as total integrated scattering measurements at lambda = 633 nm have been performed on a special layer design to suppress roughness-induced scattering. A comparison of the predicted theoretical and the measured experimental values leads to such structural parameters as packing density and the evolutionary exponent of the columns.

Cerium oxide films formed by electron-beam evaporation onto oblique substrates are shown to scatter light strongly into spatially anisotropic distributions and to exhibit large normal-incidence birefringence Δ n = n(s) - n(p). The apparatus for direct recording of a useful projection of the scatter distributions is described. Characteristic differences in scatter patterns recorded for cerium oxide, relative to those from tilted columnar titania and zirconia films, are believed to be associated with unusual microstructures recorded for cerium oxide films by scanning electron microscopy. With increasing angle of deposition, the microstructure of cerium oxide was observed to change from densely packed columns to partially isolated needlelike columns at angles that do not obey the tangent rule. In particular, deposition at 55° yielded columns nearly perpendicular to the substrate, yet the normal-incidence birefringence was large. The retardation of the films was recorded as a function of angle of incidence for propagation in the deposition plane. A turning point near 0° incidence for the 55° film confirmed that one principal axis is perpendicular to the substrate. Significant bunching of columns into rows running perpendicular to the deposition plane was recorded by scanning electron microscopy and may account for both the scatter and the birefringence.