Optical extinction spectra

Figure 6.10 Theoretical (dashed line) and experimental (solid line) optical extinction spectra of NP of radius 27nm with (thick line) and without (thin line) 5mn silica shell.

Analysis of SEM images of Ag NPs deposited on a surface (data not shown) yielded the estimate of the Ag NP diameter of c sem = 57 31 nm. Measurements of optical extinction spectra of Ag nanoparticle solution and their comparison with the predictions of the optical scattering theory [5] produced a value of dahs = 55 nm. These data are consistent with the ones previously reported [6] for Ag NPs produced by the same method. 

Study of the optical extinction spectra of the same two gold clusters, Aub and AU55, in solution leads to the same result with respect to the metal non-metal transition. The AU55 cluster core forms a metallic system characterized by collective excitation of the electrons. There is no indication of any molecular fine structure even at 2 K. The observed smearing of the band edge is responsible for damping... 

Figure 10. Optical-extinction spectra of a silver azide crystal, partially decomposed by irradiation with UV light. Tq is the incident light intensity and T is the transmitted intensity. Polarized light is traveling in the [010] direction with the electric vector parallel to [001] for curve A and parallel to [100] for curve B (after McLaren [91]).

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 Figure 6.3, the optical extinction spectra before and after thermal aimeal-ing are plotted for a comparable film sample that was deposited on quartz... 

Figure 8.5. Analytical optical extinction spectra for silver nanoparticles embedded in PMMA versus particle size.

Optical extinction spectra for a Ag nanoparticle with a fixed size of the core (4nm) and a varying thickness of the carbon sheath (from 0 to 5 nm) are shown in Figure 8.7. The maximum of the SPR bands of the particles is seen to shift... 

Figure 8.7. Analytical optical extinction spectra for 4-nm silver nanoparticles with the carbon sheath that are placed in the PMMA matrix versus sheath thickness.

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. The optical extinction spectrum of three sols A. The ultrafine dispersion of gold clusters (nuclei for catalyst preparation) 1.5 run B. The coarser sol of gold catalyst particles = 3-5 run arising from coalescence of gold clusters in A, induced by boiling the sol. C. A gold sol prepared by the traditional citrate method, = 15nm...

Figure 4. (A) Assembly of I2nm nanc article on glass monitored by optical extinction. Spectrum was collected at 5,10, IS, 30,60,120, and lOSOminutes. (B) Kinetics of gold nanopaiticle adsorption on glass measured by the change in Ext° as a function of time.

FIGURE 16.2 Typical optical extinction spectrum of dog bone-shaped nanorods, measured for an aqueous suspension (authors, unpublished work). 

In more recent optical extinction measurements on specially filtered samples [60], the weak bump had disappeared. This bump may thus have been due to damaged clusters (see Sect. 3.6) or cluster aggregates which form colloidal inclusions in the sample. The main feature of the UV-visible spectrum of AU55 in solution is then a broad absorption extending across the whole visible region. 

The normalized light extinction spectrum is identical to the photoacoustic spectrum shown in Figure 1. At 600.Onm the extinction of the laser radiation was 2% for the 9.5cm spectrophone cavity optical path. Thus, from the Beer-Lambert Law,... 

Figure 4.5 (A) Darkfield optical micrograph of a typical distribution of single Ag nanoparticles immobilized on a glass cover slip. (B) Single-particle darkfield scattering spectra corresponding to the individual Ag nanoprisms labeled in (A). The ensemble solution extinction spectrum is shown as the shaded, dashed curve for comparison. Reprinted with permission from reference 9.

Several general characteristics of photosensitizers affect their efficacy as PDT agents photophysical, photochemical and pharmacological. The photophysical/ photochemical properties include the absorption (extinction spectrum) in vivo, the quantum efficiency for generating singlet oxygen (or other active photoproducts), the photobleaching rate and the quantum efficiency for fluorescence. The characteristics of particular photosensitizers and the relationship to their molecular structure are discussed in other chapters, as are the tissue uptake and clearance and microlocalization properties. Here, we will focus on the methods, primarily optical, that may be used to measure some of these characteristics in vivo. 

Earlier studies by Kreibig and co-workers also impact on the nature of the insulator-metal transition throughout extended arrays of mesoscopic particles. These authors investigated the effect of cluster-particle aggregation by monitoring the extinction spectrum from gold clusters all the way up to a thin film of the same element. The effect of aggregation on the optical response is drastic not only are the... 

Because of the uncertainty surrounding TEM images of these smallest nanoclusters, other methods for obtaining particle size information were applied to the sol. The optical extinction in the ultraviolet-visible region of the spectrum (UV-vis) shows a trace of the plasmon feature typical of gold colloids, strongly suppressed due to finite-size effects [3] (Fig. 2, curve A). The spectrum resembles that of other gold cluster systems estimated at about 2 nm mean diameter [4], 1-2 nm [5] and about 1.2 run [6]. 

Mie theory gives a general description of light scattering by particles, and allows prediction of the extinction spectrum for a collection of particles given the particle sizes and their optical constants (20). Assuming no gaseous species are present (i.e. = 0), Equation 1 can be rewritten in terms of the extinction cross-... 

To investigate the effect of size, shape, composition and aspect ratio of metal particles on the optical properties of a silicon solar cell, a DDA study was carried out on an infinite silicon plane upon which are deposited arrays of nanorods with different surface coverage ratios ranging from 4—16% (Figure 4.5). When the nanorods are randomly fabricated, the extinction spectrum becomes very broad, in contrast to the case with a periodic structure. 

Ideal nanoshells with diameters of less than 50 nm will exhibit a single tunable extinction peak. An increase in the size of the nanosheU size beyond 50 nm leads to the introduction of multipole resonances in addition, scattering effects begin to dominate the extinction spectrum. The peak in optical extinction for nanoshells may be tuned from -520 nm into the near-infrared (NIR). 

D. gigas AOR was the first Mo-pterin-containing protein whose 3D structure was solved. From D. desulfuricans, a homologous AOR (MOD) was purified, characterized, and crystallized. Both proteins are homodimers with-100 kDa subunits and contain one Mo-pterin site (MCD-cofactor) and two [2Fe-2S] clusters. Flavin moieties are not found. The visible absorption spectrum of the proteins (absorption wavelengths, extinction coefficients, and optical ratios at characteristic wavelengths) are similar to those observed for the deflavo-forms of... 

Any appropriate spectrophotometer capable for measuring both in the ultra-violet (UV) and visible range of the spectrum must essentially consist of an optical system that should produce monochromatic light in the range 190-780 nm and a suitable device for measuring the extinction (E) precisely and accurately. 

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]. 

Extinction and absorption spectra for 0.01 jum particles with optical constants appropriate to radiation-damaged MgO (see Fig. 10.1) are also shown in Fig. 11.2. The lowest-energy absorption band among the three broad bands shows clearly in extinction but not the highest-energy band. In this instance obscuration of structure is caused by the dominance of scattering over absorption, not saturation of absorption. This is obvious from the absorption spectrum, in which all three bands are evident. To observe the band at 3.5 eV... 

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