Structure-related optical properties of thin films

Vacuum-deposited thin films have a columnar structure that includes appreciable void volume. This structure is responsible for many differences between the properties of materials in the form of thin films and in bulk. Refractive index is usually reduced and is a sensitive function of preparation conditions. Films also exhibit considerable inhomogeneity and form birefringence. Theoretical predictions of the refractive index of columnar thin films are finding confirmation in recent measurements. Moisture adsorption over the internal surface of the films and in the voids leads to instability of optical properties and a dependence on environmental conditions greatly exceeding that of bulk materials.