Российский технологический журнал (Apr 2018)
THE EFFECTIVE MEDIUM THEORY AS A TOOL FOR ANALYZING THE OPTICAL PROPERTIES OF NANOCOMPOSITES
Abstract
The spectral dependence of the dielectric permittivity of a nanocomposite sample in the near-IR range was investigated. Nanocomposites are inhomogeneous structures in which metal granules are placed in a semiconductor or dielectric matrix. Methods of effective medium are used to describe the optical and magneto-optical properties of nanocomposites. In such structures the existence of giant and tunnel magnetoresistance, giant anomalous Hall effect, large magneto-optical activity and anomalous optical absorption is possible. These effects are of both fundamental and practical interest. Using the Fresnel formula, the spectral dependences of the reflection and transmission coefficients of p-polarized light were constructed. The singular points of the given spectral dependences at λ = 1 and 4 μm were found and discussed. The composition of the nanocomposite (Cu + Si) was determined. The model spectral dependences of the dielectric constant for this nanocomposite were constructed. A good qualitative and quantitative agreement of the experimental and model spectral dependences was observed. The dielectric permittivity values for Cu + Si nanocomposite were calculated by the Maxwell-Garnett method. To date, there are several methods for describing the effective environment of a nanocomposite. The main approximation in the case of a small concentration of the metal component is the Maxwell-Garnett effective medium method, which describes the structure by means of the effective dielectric constant εeff. For medium concentrations the approach of Bruggeman is used. In the case of arbitrary concentrations, the symmetrized Maxwell-Garnett approximation works well. Since the concentration of the metal component was determined in our work, which is 7%, the method of Maxwell-Garnett effective medium method was chosen. The analysis carried out in the article makes it possible to predict the optical properties of any nanocomposite, which is important for the selection of materials with specified properties. The possibilities of using nanocomposites are discussed.
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