Permittivity in Molecular Nanofilms

Abstract

A microscopic theory of dielectrical properties of thin molecular films, i.e. quasi 2D systems bounded by two surfaces parallel to XY planes was formulated. 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 excitations can occur: bulk and surface exciton states. Analysis of the optical properties of these crystalline systems for low exciton concentration shows that the permittivity strongly depends on boundary parameters and the thickness of the film. Conditions for the appearance of localized exciton states have been especially analyzed.

Shell-Nanostructured Materials for Biopharmacy and Biomedicine

“…The most significant results that we have achieved in our previous researches [32][33][34][35], concerning the formation and the analysis of the core-shell crystalline nanomodel and its potential application in nanomedicine, can be briefly defined in the following way: on bordering surfaces of the nanofilm (here it is a nanoshell), due to extreme localization of elementary excitations, all the physical properties of the material change, therefore: − Small, thermally or mechanically stimulated disturbances can become surface waves of great amplitude, i.e. energies that can imply the braking up of crystallographic connections between the atoms of bordering planes and the decomposition of the bordering layer, and then of all the other atoms; − Heat can be more easily absorbed and surface conducted, which allows the nanolayer to be supplied with additional energy which is necessary to melt the material on bordering layers first, and the other layers afterwards;…”

Changes in Optical Properties of Molecular Nanostructures

“…The next step is transition from direct space to k-space, i.e. performing the time and space Fourier transformations [3,5]. The advantage of this transition is direct and elegant calculation of energy dispersion law.…”

“…To calculate energy dispersion law for excitons in ultra thin films, it is sufficient to resolve determinant of the system, because poles of the Green's function define exciton energies, which leads to equalizing determinant of the system with zero [3,5,6]. In Fig.…”

“…To simplify the problem we will solve the simple superlattice problem [3,8], i.e. we will assume that the energies on the site in the both films are equal (∆ a = ∆ b = ∆) and the energy transfer between layers is equal in both films (X a = X b = X s ).…”

“…Although excitons are not the only (quasi) particles that can be find in the nanostructures when external electromagnetic field is turned on, this statement is satisfactorily correct if we use the molecular crystals [2]. Following this fact, we would restrict our research on dielectric (non-conductive) molecular crystalline materials, where standard excitons Hamiltonian include Pauli-operators with unsuitable statistic and therefore we would have to cross onto Bose statistics [1][2][3]. In further calculus we would use Green's function method [4] and corresponding equation of motion in approximation of nearest neighbor, but including dimensional restrictions related to configuration and internal organization of nanostructure, in particular we would observe ultra thin films and superlattices.…”