Discrete resonant absorption in molecular nanofilms

Abstract

We have analysed the significant different optical absorption of molecular nanofilm crystalline formations. The main reason for this behaviour is in the existence of boundaries on the film structures and we needed to investigate these properties theoretically. In this process, we have done some combinations of (where possible) analytical calculations and (in other cases) numerical calculations. We have calculated the allowed energies of exciton (quasi)particles, and their appearance in nanofilms but in particular direction - perpendicular to the surface of the film. We have analysed why surface exciton localization appears in a film, and after that we calculated dielectric permittivity and optical indices (absorption and refraction). We have established that boundary parameters greatly influence optical phenomena. This influence is resonant, i.e. frequency-related and selectable (depends on what layer is calculated). We even found some particular conditions for the appearance of one (single) absorption line.

Keywords

• excitons
• ultra-thin films
• dielectric permittivity
• absorption
• refraction