Using Rouse-Fowler model to describe radiation-induced electrical conductivity of nanocomposite materials

Abstract

Abstract. Using the Rouse-Fowler (RF) model this work studies the radiation-induced electrical conductivity of a polymer nanocomposite material with spherical nanoparticles against the intensity and exposure time of gamma-ray, concentration and size of nanoparticles. The research has found the energy distribution of localized statesinduced by nanoparticles. The studies were conducted on polymethylmethacrylate (PMMA) with CdS nanoparticles. IntroductionNanocomposite materials are materials formed by inclusion of nanoparticles into some matrix material. As a result, we can create a new functional material with unique electro physical properties. PMMA+CdS or CdSe nanocomposite allows creation of new types of photo galvanic and optoelectronic devices [1][2]. It is important to consider the possibility of using these devices under increased radiation (space, nuclear engineering, etc.). Therefore, the study of the nanocomposite radiation resistance is an important and relevant task [3]. Particular attention is given to spherical semiconductor nanoparticles such as CdS or CdSe due to the fact that their fluorescence band covers whole visible, near-IR and near-UV bands depending on the particle size. It is known that such size dependent properties are related to quantum confinement effects that are more pronounced with the smaller nanoparticle size. Thus nanocomposites with the nanoparticle size less than 10 nm possess the most interesting electrophysical properties. The maximal realization of electrophysical properties of CdS and CdSe nanoparticles requires their isolation from each other, that is why the nanoparticle concentration normally does not exceed 10 vol.%.Using the Rouse-Fowler (RF) model, this work studies the radiation-induced electrical conductivity of the polymer nanocomposite exposed to gamma-rays. According to works [4][5][6], phenomena related to the radiation-induced electrical conductivity of polymers are best described by the Rouse-Fowler model. There are analytic and numerical solutions [7][8][9][10][11] for the model variations where either the spectrum of localization centers (traps) in the bandgap has only one or two states or the distribution of trap energy states follows the exponential law. Nanocomposite materials are characterized by existence of additional centers of localization in the bandgap. The energy distribution of these centers depends on the shape, size and concentration of nanoparticles. Thus the need to describe electrophysical properties of nanocomposites requires the RF model generalization for a certain energy distribution of localization centers in the bandgap.

Population Kinetics of Localized States in Nanocomposite Materials Under Exposure to Radiation

“…We showed [12], that the values of radiation induced electrical conductivity calculated by this method are in the good agreement with results obtained by other authors.…”

“…Previously, we showed that the ionization of inclusion has the contribution to the ionization of nanocomposite materials, comparable with the ionization of matrix material [12].…”

“…1 (~10 6 s). The equilibrium value of the radiation-induced electrical conductivity depends on the size and the concentration of the nanoparticles due to the appearance of additional charge carriers, which release from the impurity centers [12].…”

“…To calculate the energy spectrum of localized states originated from the spherical nanoparticle introduction into the matrix material, we solved the Schrodinger equation with the following potential [12]: [12]. Rouse-Fowler equation system, which describes the kinetics of free and localized on traps carrier, has the form:…”

“…where n , p are the concentrations of free electrons and holes; m n and l p are the concentrations of trapped electrons and holes; 0 m and 0 l are the numbers of energy levels for electrons and holes; The last summands in (3) and (4) take into account the fact that under ionization of the donor inclusion the electron localized on the deepest trap becomes free, while the ionization of the acceptor inclusion leads to the hole localization on the top level [12].…”