Basics of optical engineering – Analysis of environmental and quantum size effects on the optical characteristics of molecular crystalline nanofilms

Abstract

© 2018 Elsevier B.V. The basis of modern optical engineering involves makes finding ways to design predefined optical (and in general – physical) properties of nanoscopic patterns. The boundary parameters of nano-patterns depend on (small) dimensions and the type of nanostructure substance, the external environment, as well as the form and the technical–technological of aspect of production. Fundamental properties of nano-structures can be drastically changed by changing these parameters. We have investigated the optical specificities of molecular dielectric crystal nanofilm under the influence of different confinement conditions. This paper presents a model of crystalline ultrathin molecular film and an analysis of dielectric, i.e. optical properties of these spatially much bounded structures – in their entirety. Using the two-time dependent Green's functions, the energy spectrum, the possible exciton states and their space distribution were determined and the dynamic permittivity was calculated. It was shown that the appearance of localized states in the boundary layers of the film depends on the thickness and the changing values of the system parameters in the boundary areas of the film. These localized states define the schedule and determine the number of resonant absorption peaks in the infrared region of the external electromagnetic radiation (EMR). Analytical analysis of the impact of the boundary parameters on the changes of the dielectric and optical properties of the nanofilm, as compared to the same properties of bulk samples with identical crystalline and chemical structure, is impossible. Thus, a software package (dubbed JOIG_S) has been developed and applied to perform the numerical analysis and plot graphic displays of the relation between microscopic (exciton) and macroscopic (dielectric and optical) properties as a function of the frequency of an external electromagnetic field (EMF), for a specified set of values of the boundary parameters. Optical, i.e. absorption and refraction properties of observed nanostructures demonstrate very narrow and strictly discrete characteristics. Characteristic resonant peaks appear in the dependence of the absorption index on the frequency of external EMF. All peaks fall into infrared region and indicate absorption of corresponding external EM frequencies. The number and distribution of these peaks depend on the number of layers in the film and the perturbation parameters, as a consequence of the quantum size and confinement effects. This proved that the outer environment of the film affects the given fundamental properties of a nano film, i.e. their choice/change directly controls the optical properties of the film. Such an approach could be considered as a kind of optical engineering.