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Based on microscopic (exciton) theory of optical properties of perturbed ultrathin molecular films, the absorption, reflection, and transparency indices were formulated and presented in dependence on frequencies of an external electromagnetic field in near IR region. It has been shown that all optical properties depend on the position of the crystal plane with regard to boundary planes of the film. We have determined and analyzed optical properties relations for the whole film structure based on the consideration for multiple reflection, absorption, and transparency in observed multilayered structure. The four-layered dielectric nanofilms with different boundary conditions on surfaces were analyzed and some discrete resonant absorption lines were obtained. Their number, position, and distribution depend on the boundary parameter values, i.e. on the type and the technological process of their preparation/fabrication. Practically monochromatic absorption may occur. Unlike the corresponding bulk-samples, which are total absorbers throughout the near IR, region, in ultrathin films will appear selective and discrete reflection and transparency. These results could provide a great contribution to optical engineering of nanostructures, especially in technology of designing of new electronic and photonic equipment, and for nanoparticles construction for drug carrier/delivery in nanomedicine.

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.

In this paper we have applied theory of exciton on the ultrathin molecular dielectric films—layered nanostructures with the thickness up to 20 atomic layers. We have calculated optical properties: the absorption, reflection and transparency indices as the function of frequencies of external electromagnetic field in near IR region. We showed that one of the significant properties of the ultrathin film is their interaction with substrate or environment, which could be represented through perturbation parameters. For symmetrically perturbed films, all optical properties depend on the position of the crystal plane with regard on boundary planes of the film. We have analyzed optical properties for the whole film structure based on the consideration for multiple reflection, absorption and transparency. The theory has been applied for the four-layered dielectric nanofilms with various different boundary conditions on film surfaces. As a result, we obtain some discrete resonant absorption lines, where their number, position and distribution strongly depend on the boundary parameter values, i.e. on the type and the technological process of their preparation/fabrication. While balk made from the same material totally absorb the near IR region, in ultrathin films will appear only selective and discrete absorption (also with reflection and transparency too). These results could be used in optical engineering of nanostructures and technology of designing of new electronic, photonic and photovoltaic devices. In addition, particularly designed nanoparticles are used in nanomedicine, whose behavior strongly depends on external electromagnetic field, in purpose of drug carry or delivery.

Recent research in nano-optical engineering and in nanomedicine as well, seeks for methods of construction of various types of nano-markers, nano-carriers, and ways to deliver drugs to the exactly determined regions of body. In this process it is important to find methods of recognition of certain types of molecules. It is obvious that optical recognition would be the easiest and the most effective way to do it. Our research presents a model of a molecular ultrathin crystalline film and generated exciton system inside it and corresponding methodology of analysis of their optical characteristics. Properties of these spatially very restricted structures are very sensitive to their surrounding surfaces. Using the two-time Green’s functions adapted for crystalline structures with symmetry breaking, and graphical-numerical software, we have calculated the energy spectra and possible exciton states. We have shown that the appearance and the presence of localized states on the surfaces and in the boundary layers of the film depend on the thickness of the film and the film surroundings, presented through the perturbation of parameters on surfaces. Optical properties in these structures demonstrate discrete and very selective resonant absorption spectra, depending on the perturbation on their surfaces.

The changes of optical properties under boundary presence in molecular crystal nanofilm were theoretically investigated in this work. The dispersion law and states of excitons as well as their space distribution along boundary direction have been determined using adjusted Green's function method and also by combined analytical and numerical calculations. On the basis of real and imaginary part of relative permittivity, both absorption and refraction indices were determined, and the influences of boundary parameters on occurrence of a very selective and strictly discrete absorption were analyzed.

We have formulated a microscopic theory of optical properties of ultrathin molecular films (nanofilms), i.e. quasi 2D systems parallel to XY planes bounded by two surfaces. Exposure of nanofilms to the external electromagnetic fields has result in creation of excitons – but different than bulk ones. Harmonic exciton states were calculated using the method of two-time, retarded, temperature dependent Green’s functions. It has been shown that two types of optical excitations can occur: bulk and surface exciton states. Exciton energy dispersion law shows discrete behavior with non-zero values. Analysis of the dielectric properties of these crystalline systems for low exciton concentration shows that the permittivity strongly depends on boundary parameters and the thickness of the film. In addition, permittivity shows very narrow and discrete dependence of external electromagnetic field frequency, which is a consequence of both resonance and quantum size effects. Influences of boundary conditions on optical characteristics (through analyses of dynamical absorption coefficient) of these nanostructures were specially and in details explored.

A microscopic theory of optical properties of ideal ultrathin molecular films, was formulated in bosonic and nearest-neighbor approximation. Calculating of dynamical permittivity by the single-pole Green's functions have shown that the threshold of light absorption, refraction, reflection and transmission can be moved along frequencies, changing the film thickness. This can give a great contribution to practical ultrathin film engineering, especially to construction of drug delivery nanoparticles in nanomedicine.