Metallic colloidal scattering

Kerker M., Electromagnetic Model for Surface-Enhanced Raman-Scattering (Sers) on Metal Colloids, Accounts Chem. Res. 1984 17 271-277. 

Dou, X.M. and Ozaki, Y. (1999) Surface-enhanced Raman scattering of biological molecules on metal colloids basic smdies and applications to... 

If the measured extinction is due to metal colloids, the relative amounts of absorption and scattering will depend on particle size. In contrast, clusters of nitrogen might be expected to cause extinction which is due to scattering but not to absorption for the wavelength range of interest. It is possible to deter-... 

In 1906, J. C. Maxwell Garnett used the Maxwell Garnett theory, equation (12), for the first time to descibe the color of metal colloids glasses and of thin metal films. Equation (12) can be deviated from the Rayleigh scattering theory for spherical particles [21], or from the Lorentz-Lorenz assumption for the electrical field of a sphere and the Clausius-Mossotti Equation by using the polarizability of an metal particle if only dipole polarization is considered [22]. 

Raman spectroscopy is not particularly surface sensitive but a surface enhanced Raman scattering (SERS) effect is observed on some metals (copper, gold, silver, nickel etc). On an appropriately prepared (roughened) surface or on metal colloids the surface coverage of molecules can be measured by Raman spectroscopy with high sensitivity. 

Several techniques are commonly used to measure the size distributions of metal colloid particles. Electron microscopy. X-ray diffi ction, and small angle X-ray scattering are the most commonly used, although dassical methods such as sedimentation rates are sometimes reported. The techniques whidi have been extensively applied to the sizing of polymer colloids and emulsions, [183] such as light scattering and neutron scattering, have been only rarely applied to the characterization of metal sols. [103, 151, 153, 184]... 

Vibrational Raman scattering [16-22]. Surface-enhanced Raman scattering (SERS) refers to the observation that certain molecules adsorbed on specially prepared metal surfaces or on metal colloids show Raman spectra with some bands enhanced by a factor 10 -10 " in comparison with the ones of non-adsorbed molecules. Recently, huge enhancement factors of... 

Recently, various sol-gel based recipes incorporating metal colloids have been shown to result in successful SERS substrates (49, 50, 52-57). Large Raman enhancements have been found for nano-sized metal particles dispersed in the resulting gel structure, in part, due to the large stabilized metal surface areas available to molecular-sized scatterers. In contrast, the sol-gel derived SiOa SERS substrate produced by the procedure described here is covered by immobilized clustered aggregates of monodispersed sized gold nano-particles that have been grown in-situ. 

In practice, the invariant can be used for the purpose of calibration to absolute scattering intensity by means of samples for which the absolute invariant can easily be computed. For this purpose colloidal suspensions of noble metals with known volume concentration are suitable [96], All the noble metal particles must be small enough so that they really contribute to the observed particle scattering. They must not agglomerate. 

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