Optical extinction simulation

Figure 7.4 Influence of nanorod shape on its optical extinction properties, as simulated using the discrete dipole approximation, (a) different aspect ratios, fixed volume, (b) fixed aspect ratio, variable volume, (c) aspect ratio and volume fixed, variable end cap geometry, (d) convexity of...

In this chapter, we studied the formation of silver nanoparticles in PMMA by ion implantation and optical density spectra associated with the SPR effect in the particles. Ion implantation into polymers carbonizes the surface layer irradiated. Based on the Mie classical electrodynamic theory, optical extinction spectra for silver nanoparticles in the polymeric or carbon environment, as well as for sheathed particles (silver core -l- carbon sheath) placed in PMMA, as a function of the implantation dose are simulated. The analytical and experimental spectra are in qualitative agreement. At low doses, simple monatomic silver particles are produced at higher doses, sheathed particles appear. The quantitative discrepancy between the experimental spectra and analytical spectra obtained in terms of the Mie theory is explained by the fact that the Mie theory disregards the charge static and dynamic redistributions at the particle-matrix interface. The influence of the charge redistribution on the experimental optical spectra taken from the silver-polymer composite at high doses, which cause the carbonization of the irradiated polymer, is discussed. Table 8.1, which summarizes available data for ion synthesis of MNPs in a polymeric matrix, and the references cited therein may be helpful in practice. 

There is strong evidence that massive injections of particulate material have occurred over Earth s history and that such episodes may have coincided with the extinction of species (Claeys et al., 1992). Simulations of the climatic consequences of large-scale nuclear war indicate that land temperatures over the 30 to 70 " N latitude zones would decrease by 5 K, 13 K, and 22 K, respectively, for smoke optical depths of 0.3, 1.0, and 3.0 (Turco et al., 1990). 

Simulated extinction spectra for Ag nanoparticles embedded in a polymer matrix to compare with experimental data shown in Figure 8.4. In theoretical calculations, we used the complex value of the optical constant CAg in the visible range [48] that was obtained by measurements on a set of fine silver particles. Such an approach [48] takes into account limitations imposed on the electron free path in particles of different size and electron scattering at the particle-insulator interface [49] and thus yields a more exact value of eAg than does the procedure of correcting optical constants for bulk silver [50], The complex value of Epmma for the polymer matrix was found elsewhere [42]. The extinction was calculated for particles of size between 1 and 10 nm (according to the MNP sizes in Figure 8.2). 

Lion that the polymer irradiated is completely carbonized, which was used in the simulation (Figure 8.6), does not become a reality when the process lasts for a long time. Below, the variation of the extinction spectra with amount of carbon in the PMMA layer is analyzed in terms of a model that considers the optical properties of silver MNPs covered by the amorphous carbon sheath. 

Although DDA simulations for nanoparticles mostly focus on extinction efficiency, as this is usually measured experimentally, several researchers have studied its constituents—absorption and scattering efficiencies—separately [132, 135, 136], This should result in a better understanding of DDA errors, especially their size dependence. Moreover, absorption efficiency is relevant to practical applications involving optical heating of nanoparticles. 

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