Plasmon extinction

Figure 16.6 Tunability of the plasmon resonance maximum in gold nanostructures. Variation of the surface plasmon extinction maximum with (a) nanospheie diameter D (b) nanoshell total radius R2 with fixes R1/R2 = 0.857 (c) nanoshell core/shell ratio R1/R2 at fixed R2 = 70 nm (d) nanorod effective radius = (3V/4II) / at fixed aspect ratio R = A/B = 3.9 (e) nanorod aspect ratio R at fixed r ff = 11.43 nm. (Reproduced with permission firam P. K. Jain et al., 2006. J. Phys. Chem. B 110 7238-7248. Copyright 2006 American Chemical Society.)...

Figure 12. (A) Time-dependent change in sur ce plasmon extinction at SSO nm as a result of specific binding of streptavidin to biodn ted gold nanoparticles surfiwe. (a) 100 pg/ml, (b) 30 pg/ml, (c-e) 10 pg/ml, (f) S tg/ml, (g) BSA, (h) biotin saturated streptavidin (i) human IgG. (B) Absorbance change at SSO nm as a fbnction of strq>tavidin concentration.

Localized plasmon resonance on noble metal nanostructures Noble metal nanostructures exhibit a strong UV visible extinction band with its peak position affected by the dielectric constant and thickness of the material surrounding the nanostructures 7,11 13... 

The same evolution of the absorption spectrum with the dose has been found in a high dose rate for various values of the Ag and Au ion fraction in the initial solution. Clusters Agi. Au are alloyed with the same composition. The maximum wavelength and the extinction coefficient Smax of the alloy depend on x. The experimental spectra are in good agreement with the surface plasmon spectra calculated from the Mie model at x values for which optical data are available (Fig. 12) [102]. Similar calculations were carried out for the alloy Ag Pdi obtained at a moderate dose rate [180]. 

Figure 12 Top Maximum wavelength of the plasmon band of alloyed gold-silver clusters as a function of the mole fraction x of gold in alloyed gold-silver clusters, produced at the dose rate 7.9 MGy hr and the dose 20 kGy. Experiments, calculated values by Mie model. Bottom Extinction coefficient at the maximum of the plasmon band as a function of the mole fraction x of gold in alloyed gold-silver clusters. Experiments, calculated values from Kreibig equation [74] with r = 5 nm A with r = 3 nm. (From Ref 102.)...

As an example of extinction by spherical particles in the surface plasmon region, Fig. 12.3 shows calculated results for aluminum spheres using optical constants from the Drude model taking into account the variation of the mean free path with radius by means of (12.23). Figure 9.11 and the attendant discussion have shown that the free-electron model accurately represents the bulk dielectric function of aluminum in the ultraviolet. In contrast with the Qext plot for SiC (Fig. 12.1), we now plot volume-normalized extinction. Because this measure of extinction is independent of radius in the small size... 

Extinction calculations for aluminum spheres and a continuous distribution of ellipsoids (CDE) are compared in Fig. 12.6 the dielectric function was approximated by the Drude formula. The sum rule (12.32) implies that integrated absorption by an aluminum particle in air is nearly independent of its shape a change of shape merely shifts the resonance to another frequency between 0 and 15 eV, the region over which e for aluminum is negative. Thus, a distribution of shapes causes the surface plasmon band to be broadened, the... 

Another example listed in the table is graphite, the Frohlich mode of which is near 5.5 eV (2200 A) the boundaries of the negative e region are about 4 and 6.5 eV. The graphite surface plasmon has been tentatively identified as responsible for a feature in the interstellar extinction spectrum (see Section 14.5). 

Prominent extinction peak at 2170 A (5.7 eV) Surface plasmon in graphite... 

The most prominent features of the empirical photoabsorption spectrum of C60 are two bands located at about 6 and 23 eV (Fig. 1.2, 50-200 nm). These bands have been interpreted as collective excitations similar to the n and a plasmon. In the fullerene C60 these type Mie plasmons are due to the strong delocalization of the valence electrons. The c-type is much more intense than the 7r-type plasmon. It has been proposed (Braga et al. 1991) that the n transition could be related to the UV bump in the interstellar extinction. 

The far-UV to near-IR EF.T, spectrum of the unexposed C60 film is exhibited in Fig. 2.2a, in close agreement with spectra reported previously for thick C60 films on Si(100) (Gensterblum 1991). The characteristic camel back features, which exclude C60 as a carrier of the interstellar extinction, are readily observed at 195 and 260 nm. The three peaks at 260, 335 and 420 nm are seen in absorption spectroscopy (AS), and correspond to dipole-allowed,1A - Tlu, single-electron n-n transitions in the C60 molecule (Leach 1992 Hare et al. 1991). The intense peak at 195 nm is the so-called ir-plasmon that results from a collective excitation of the molecular TT-elcctron subsystem. The collective nature of this excitation is affirmed by our experimental observation that its intensity is variable upon changing the primary electron energy of the EEL spectrometer (Lucas 1992). Additionally, this band is broadened and blue-shifted when compared to the narrower transition seen in AS... 

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