https://onlinelibrary.wiley.com/doi/pdf/10.1002/andp.19083300302

Beiträge zur Optik trüber Medien, speziell kolloidaler Metallösungen

In 1978 it was discovered, largely through the work of Fleischmann, Van Duyne, Creighton, and their coworkers that molecules adsorbed on specially prepared silver surfaces produce a Raman spectrum that is at times a millionfold more intense than expected. This effect was dubbed surface-enhanced Raman scattering (SERS). Since then the effect has been demonstrated with many molecules and with a number of metals, including Cu, Ag, Au, Li, Na, K, In, Pt, and Rh. In addition, related phenomena such as surface-enhanced second-harmonic generation, four-wave mixing, absorption, and fluorescence have been observed. Although not all fine points of the enhancement mechanism have been clarified, the majority view is that the largest contributor to the intensity amplification results from the electric field enhancement that occurs in the vicinity of small, interacting metal particles that are illuminated with light resonant or near resonant with the localized surface-plasmon frequency of the metal structure. Small in this context is gauged in relation to the wavelength of light. The special preparations required to produce the effect, which include among other techniques electrochemical oxidation-reduction cycling, deposition of metal on very cold substrates, and the generation of metal-island films and colloids, is now understood to be necessary as a means of producing surfaces with appropriate electromagnetic resonances that may couple to electromagnetic fields either by generating rough films (as in the case of the former two examples) or by placing small metal particles in close proximity to one another (as in the case of the latter two). For molecules chemisorbed on SERS-active surface there exists a "chemical enhancement" in addition to the electromagnetic effect. Although difficult to measure accurately, the magnitude of this effect rarely exceeds a factor of 10 and is best thought to arise from the modification of the Raman polarizability tensor of the adsorbate resulting from the formation of a complex between the adsorbate and the metal. Rather than an enhancement mechanism, the chemical effect is more logically to be regarded as a change in the nature and identity of the adsorbate.

Surface-enhanced spectroscopy

Some of the greatest scientists including Poisson, Faraday, Maxwell, Rayleigh, and Einstein have contributed to the theory of composite materials Mathematically, it is the study of partial differential equations with rapid oscillations in their coefficients Although extensively studied for more than a hundred years, an explosion of ideas in the last five decades (and particularly in the last three decades) has dramatically increased our understanding of the relationship between the properties of the constituent materials, the underlying microstructure of a composite, and the overall effective (electrical, thermal, elastic) moduli which govern the macroscopic behavior This renaissance has been fueled by the technological need for improving our knowledge base of composites, by the advance of the underlying mathematical theory of homogenization, by the discovery of new variational principles, by the recognition of how important the subject is to solving structural optimization problems, and by the realization of the connection with the mathematical problem of quasiconvexification This 2002 book surveys these exciting developments at the frontier of mathematics

/pdf/the-theory-of-composites-1ruy3p9ier.pdf

The Theory of Composites

Acknowledgements 1. Introduction 2. Electromagnetic wave propagation 3. The absorption of light 4. Specular reflection 5. Single particle scattering: perfect spheres 6. Single particle scattering: irregular particles 7. Propagation in a nonuniform medium: the equation of radiative transfer 8. The bidirectional reflectance of a semi-infinite medium 9. The opposition effect 10. A miscellany of bidirectional reflectances and related quantities 11. Integrated reflectances and planetary photometry 12. Photometric effects of large scale roughness 13. Polarization 14. Reflectance spectroscopy 15. Thermal emission and emittance spectroscopy 16. Simultaneous transport of energy by radiation and conduction Appendix A. A brief review of vector calculus Appendix B. Functions of a complex variable Appendix C. The wave equation in spherical coordinates Appendix D. Fraunhoffer diffraction by a circular hole Appendix E. Table of symbols Bibliography Index.

Theory of Reflectance and Emittance Spectroscopy

Gold nanorods with different aspect ratios are prepared in micelles by the electrochemical method and their absorption spectra are modeled by theory. Experimentally, a linear relationship is found between the absorption maximum of the longitudinal plasmon resonance and the mean aspect ratio as determined from TEM. It is shown here that such a linear dependence is also predicted theoretically. However, calculations also show that the absorption maximum of the longitudinal plasmon resonance depends on the medium dielectric constant in a linear fashion for a fixed aspect ratio. Attempts to fit the calculations to the experimental values indicate that the medium dielectric constant has to vary with the aspect ratio in a nonlinear way. Chemically, this suggests that the structure of the micelle capping the gold nanorods is size dependent. Furthermore, comparison with the results obtained for rods of different aspect ratios made by systematic thermal decomposition of the long rods further suggests that the medi...

http://depa.fquim.unam.mx/amyd/archivero/RodrigoCastanedaRivera_4930.pdf

Simulation of the Optical Absorption Spectra of Gold Nanorods as a Function of Their Aspect Ratio and the Effect of the Medium Dielectric Constant

The present paper contains a discussion of some optical properties of a medium containing minute metal spheres. The discussion is divided into two Parts: the first Part dealing with colours in metal glasses, in which the proportion of volume occupied by metal is small; the second Part dealing with metal films, in which this proportion may have any value from zero to unity. In Part I. the observations of Siedentopf and Zsigmondy beyond the limit of microscopic vision (‘Ann. der Phys.,’ January, 1903) are discussed. It is shown that the particles seen in a gold ruby glass are particles of gold which, when their diameters are less than 0.1μ, are accurately spherical. I have endeavoured to show that the presence of many of these minute spheres to a wave-length of light in the glass will account for all the optical properties of “regular” gold ruby glass, and that the irregularities in colour and in polarisation effects sometimes exhibited by gold glass are due to excessive distance between consecutive gold particles or to excessive size of such particles, the latter, however, involving the former. It is also shown that the radiation from radium is capable of producing in gold glass the ruby colour which is generally produced by re-heating. The method adopted enables us to predict from a knowledge of the metal present in metallic form in a glass what colour that glass will be in its “regular” state.

/pdf/colours-in-metal-glasses-and-in-metallic-films-1ft6dzmvla.pdf

J. C. M. Garnett

Papers

Colours in Metal Glasses and in Metallic Films