Gold optical constants

It is well known that the SPR may be registered as the sharp minimum of the reflection coefficient for the plane-parallel light which depends on the incidence angle. The position of the resonance angle and the minimum depth of the incidence are determined by the parameters of the metal layer, and the optical constants of the external medium. As molecules adsorb and interact at the gold surface, the dielectric properties of the formed layer change, which leads to the transformation of the resonance curve and to the displacement of the resonance angle [7, 9, 15]. 

The shapes of the absorption band cease to be independent of size for particles smaller than about 26 A, which suggests that the bulk dielectric function is inapplicable. Indeed, the broadening and lowering of the absorption peak can be explained by invoking a reduced mean free path for conduction electrons (Section 12.1). Thus, the major features of surface modes in small metallic particles are exhibited by this experimental system of nearly spherical particles well isolated from one another. But when calculations and measurements with no arbitrary normalization are compared, some disagreement remains. Measurements of Doremus on the 100-A aqueous gold sol, which agree with those of Turkevich et al., are compared with his calculations in Fig. 12.18 the two sets of calculations are for optical constants obtained... 

Fig. 88. Theoretical spectra of gold-coated silver colloids. The optical constants were taken from Johnston and Christy [536], The dielectric constants were corrected for the effect of the mean free path using the method proposed [537] by Kreibig [534]...

In general for a highly reflective sample, 50 to 60 percent of the energy is lost through the reflection optics. If the optical constants of the film are known, the thickness of the film can be calculated based on optical theory 134-144>. Studies have been made of thin films of poly(methyl methacrylate) depolymerization on gold, nickel and zinc surfaces using ERS 135) and FT-IR. 

The optical constants for BPA-PC at the fundamental vibrational frequencies were determined by application of the techniques described above. Values of ri2 and k2 measured for the BPA-PC absorption at 1775 cm , as well as the optical constants for air (n, = 1.0, 0.0) and for gold (n = 4-2. kj = 27.6 [19]), were used to predict IR-RA values at 1775 cm for BPA-PC films ranging in thickness from 0.01 to 10 pm on gold substrates. Calculations were performed for both polarization states using Eq. 2. Effects of the substrate properties on these calculations are minor. For example, using the optical constants of aluminum (n = 6.8, kg = 32.0 [19]) resulted in changes of <1% in the values obtained. 

Fig. 9.2 Angular dependences of the phase shift (a), mean square electric field strength (MSEFS) (b), and reflectivity (c) for an air/Au interface at 1500 cm Optical constants for gold at this wavenumber are n = 3.04, /c=45.25.

Figure 9.22 illustrates the procedure. Plot A represents the calculated spectrum of 6.2x10" ° mol cm" of pyridine molecules homogeneously distributed within a 7.2 pm thick layer of D2O between the gold electrode and the hemispherical ZnSe window. The spectrum was calculated from optical constants of pyridine shown in Fig. 9.14 using Eq. (52). This spectrum is equal to... 

For the calculations, two different sets of optical constants were used for gold. The first set was taken from values for evaporated thin films [151], while the second corresponds to a single crystal [153]. The (uncoated) gold sols used had a maximum at 518.5 nm (in water), whereas the data of Johnson and Christy lead to a predicted peak at 521.5 nm, and those of Weaver at 527, a difference of 3.5 and 9.5 nm respectively. 

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