Embedded nanoparticles optical properties

Optical properties of metal nanoparticles embedded in dielectric media can be derived from the electrodynamic calculations within solid state theory. A simple model of electrons in metals, based on the gas kinetic theory, was presented by Drude in 1900 [9]. It assumes independent and free electrons with a common relaxation time. The theory was further corrected by Sommerfeld [10], who incorporated corrections originating from the Pauli exclusion principle (Fermi-Dirac velocity distribution). This so-called free-electron model was later modified to include minor corrections from the band structure of matter (effective mass) and termed quasi-free-electron model. Within this simple model electrons in metals are described as... 

A key issue in nanostructured materials is the dipole coupling between nanocrystals which will cause the optical properties of a nanocrystal ensemble to become like those of the bulk material. There has been extensive investigation of the interactions between particles embedded within media for a range of boundary conditions. We have found that the effective dielectric function given by Eq. (10), based on the Maxwell-Garnett model [1] is very accurate for quite dense nanocrystal arrays. In practice, one measures the transmittance of a thin film of the dense nanoparticle based film. Conventional solutions are simply... 

Total energy calculations have been performed to understand the role of oxidation on the structural, electronic and optical properties of Si nanoclusters. Our aim is to explain the peculiar properties of aged porous Si samples, heavily oxidized Si nanoparticles and embedded Si nanocrystals. We have studied two types of structures isolated H-covered clusters, replacing Si-H bonds with various Si-0 bonds and Si nanoclusters embedded in a SiOz matrix. Regarding the isolated clusters we find that the optoelectronic properties depend on the type and the number of Si-O bonds at the cluster surface. For the embedded systems our results show that a close interplay between chemical and structural effects plays a key role in the light emission processes. 

The optical properties of metal nanoparticles embedded in an insulating host differ substantially from the optical properties of bulk metals. Under the influence of an electrical field, there is a plasmon excitation of the electrons at the particle surface. This resonance, which takes place at a certain energy of the incident light, results in an optical absorption, the so-called plasmon absorption or plasma resonance absorption [1,2]. 

For the calculations of the optical properties of polymer films with embedded nanoparticles, two routes can be selected. In the exact route, the extinction cross sections Cact(v) of single particles are calculated. The calculated extinction spectra for single particles—or, better, a summation of various excitation spectra for a particle assembly—can be compared with the experimental spectra of the embedded nanoparticles. In the statistic route, an effective dielectric function e(v) is calculated from the dielectric function of the metal e(T) and of the polymer material po(v) by using a mixing formula, the so-called effective medium theory. The optical extinction spectra calculated from the effective dielectric functions by using the Fresnel formulas can be compared with the experimental spectra. 

In view of the specific phase structure of the polymer irradiated, it is of interest to analyze the optical properties (extinction) of Ag nanoparticles embedded in the amorphous carbon matrix (C matrix). For this system, the extinction cross-section spectra versus particle size dependence (Figure 8.6)... 

When analyzing the optical properties of nanoparticles embedded in a medium, one should take into account effects arising at the particle-matrix interface, such as the static and dynamic redistributions of charges between electronic states in the particles and the environment in view of their chemical constitution [59]. 

In this study, the possibilities of using polymers containing silicon nanopaiticles as effective UV protectors are considered. First, the stmcture of nc-Si obtained under different conditions and its aggregates, their adsorption and optical properties was studied in order to find ways of control the UV spectral characteristics of mirlti-phase polymer composites containing nanocrystalline silicon. Also, the pirrpose of this work was to investigate the effect of the concerrtration of siUcon nanoparticles embedded in polymer matrix and the methods of preparation of these nanoparticles on the spectral characteristics of such nanocomposites. On the basis of the data obtained, recommendations for designing UV protectors based on these nanocomposites were formrrlated. 

At present, the major focus of the researchers is on the nanocomposite materials based on the nanoparticles of metals and their compounds stabilized within a polymeric dielectric matrix [1-4]. The dielectric and optical properties of these materials have been demonstrated to be highly dependent on the size, structure, and concentration of the nanopartides, as well as on the type of polymeric matrix [5-8]. These have shown the possibility of the purposeful change of parameters of the nanocomposite materials such as electrical conductivity, complex permittivity, refraction coefficient, and so on. It is believed that these materials would demonstrate low acoustic impedance because they are based on the polymeric matrix [9]. At that, the impedance value should be varied within certain limits by adjusting the parameters of the embedded nanopartides. All of these would allow one to use these materials for low disturbing substrates in various devices based on the waves in thin piezoelectric plates [10]. 

Nanocomposites containing metal nanoparticles have attracted a great deal of attention, with resulting magneto-optical properties that strongly depend on the structure, size, and dispersion of the embedded particles looking for their scientific and industrial applications in areas such as optical fiber sensors, optical isolators, information storage, and so on. The narrow particle size distribution and... 

Metal nanoparticles embedded in a dielectric are known to exhibit interesting optical properties resulting from collective electronic excitations at the interfece between the metal and the dielectric matrix, leading to surface plasmon... 

With advances in nanotechnology, quantum dots are ubiquitous in surfaces with myriad applications in electrochemistry. In this chapter, we discuss the numerical modelling of quantum dots both the spherically symmetric (metal or semiconductor) dots embedded in a matrix (usually a dielectric) and the hemispherical metal dots (a.k.a. nanoparticles or thin-film islands) supported by a substrate (again, usually a dielectric). We are particularly concerned about the optical properties of quantum dots, since the interaction of light with quantum dots is used widely for several applications in surface electrochemistry - from characterization of the thickness and quality of thin films, to the development of surface sensors - as well as in nanoelectronics and quantum computing. 

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