Silver particles extinction

Silver nanoparticles can be deposited on Ti02 by UV-irradiation. Deposition of polydisperse silver particles is a key to multicolor photochromism. The nanoparticles with different size have different resonant wavelength. Upon irradiation with a monochromatic visible light, only the resonant particle is excited and photoelectrochemically dissolved, giving rise to a decrease in the extinction at around the excitation wavelength. This spectral change is the essence of the multicolor photochromism. The present photoelectrochemical deposition/dissolution processes can be applied to reversible control of the particle size. 

Absorption resonances resulting from excitation of surface modes are accompanied by scattering resonances at approximately the same frequencies this was pointed out following (12.26). In most experiments transmission is measured to determine extinction, which is nearly equal to absorption for sufficiently small particles. However, surface mode resonances have been observed in spectra of light scattered at 90° by very small particles of silver, copper, and gold produced by nucleation of vapor in an inert gas stream (Eversole and Broida, 1977). The scattering resonance peak was at 3670 A, near the expected position of the Frohlich mode, for the smallest silver particles. Although peak positions were predictable, differences in widths and shapes of the bands were concluded to be the result of nonsphericity. 

Fig. 4.2. Extinction spectra of spherical silver particles with radii 20-100 nm.

Fig. 4.4 shows extinction spectra from many different shaped silver particles (spheres, cylinder, cube, prism, pyramid), all for an effective radius (radius of a sphere of equal volume) of 50 nm. This shows very clearly that the plasmon maximum is strongly shape... 

Extinction of Silver Particles in Dependence of Surrounding Matrix... 

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). 

Extinction of Silver Particles with Carbon Shell... 

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. 

Figure 2. Calculated absorption, scattering, and extinction cross-section from a 40 nm diameter Ag particle and a 60 nm diameter Au particle. The spectrum from the silver particle has a sharp resonance and its extinction is equally split between scattering and absorption components, udiereas, the 60 nm diameter gold particle has a broader resonance and is dominated by absorption.

Fig. 12 a Extinction spectra of aqueous suspensions of rodhke silver particles as a function of ageing time at 25 °C b density functions of the aspect ratio distribution for freshly prepared silver nanorods (black solid line) and for rodKke silver particles aged for 24 h (blue dashed line) and 17 d (red dashed-dotted line) at 25 °C (adopted from Damm et al. [8]) [61]... 

When a nanoporous Ti02 film consisting of Ti02 nanoparticles is used instead of the single crystal, the extinction band of silver nanoparticles deposited by UV-irradiation is much broader. This is probably because the nanopores in the Ti02 film mold the silver nanoparticles into various anisotropic shapes [9], although direct observation of the particles in the nanopores is difficult. 

Wang and Kerker" and Chew and Wang" " have presented a theoretical treatment, based on the electrodynamic approaches used for the SERS problem, and provide a full description of the extinction of the dye-coated spheroids. They also calculated the luminescence enhancement, and find it to be up to 10" on silver for optimal wavelengths and particle shapes. 

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