| Surface-enhanced Raman scattering (SERS) enhancement is related to the wavelength of the exciting laser, the size and morphology of the metal substrate, the quantities of the absorbate and so on. The development of SERS and SERRS has made much progress in analytical application. The lowest concentration of the absorbate in the solution can reach 10-12 mol/L by using of SERS technique. SERRS is more sensitive than SERS and thus it can even detect several molecules in lnL sample solution.The evolution of SERS technique and the broadening of SERS applications are dependent on the development of SERS substrates. Thus, the preparation and properties of SERS substrates become important to develop SERS as a usual analytical tool. However, the stability, sensitivity, selectivity and reproducibility of the present SERS substrates can not meet various analytical purposes.On the basis of the above facts, we focus our study on the preparation of SERS substrates and SERS application in various fields, as well as the SERS mechanisms from theoretical and experimental ways. We employed molecular spectroscopy to investigate the relationship between the structure and function ofSERS substrates, and further explored the optical characteristics and properties of such nanomaterials.Theoretical Analysis of Nano Materials on Spectral Properties.The spectral characteristic of the materials can indicate its component, structure and morphology. Moreover, combined with it optical properties, we can investigate the relation between the structure and function of such materials and further lay a physical foundation on selecting and designing these materials for various purposes.1. We gave the enhanced factor of the local field around the Ag nanoparticle in external laser beam field. The dielectric function of some metals (Au, Ag, Cu) at optical band is analyzed. The result of calculation demonstrates that Ag is the best metal for surface enhanced Raman scattering. On roughed Ag surface, Raman spectrum can be increased by six orders of magnitude, when surface plasma resonance (SPR) is excited. The analysis also demonstrates that many factors can affect the intensity of SPR. First, while the dielectric constant out of the metal particle increases, the frequency of SPR shifts to low frequency (LF). And the enhancement of located electromagnetic field also increases. Secondly, if the Ag particle is ellipsoidal, the frequency of SPR will shift to LF while the ratio of major axis to minor axis increases. Finally, with the dimension of sphere increasing, the variety of enhancement is up first, then down. The optimized dimension is about 50 nm.2. The IR and Raman spectra of BVPP were calculated. All the calculations were completed at the work station of SGI-OCTAIN-TWO through Gaussian 98 program after the optimization of the molecule according to the symmetry of C2h. And the assignments of IR and Raman spectra were shown.The difference between the vacuum-deposited Ag island film and the self-assembled Ag colloid film were also compared.3. Absorption spectra of spherical particles were investigated with Mie theory on the basis of classical electrodynamics. The calculated spectra by the Mie theory are compared with the experimental results. For those nonspherical particles, we introduced a numerical method named discrete dipole approximation (DDA) . It can be applied to the arbitrary particles and their environments. Then, we described the applications of DDA to problems of recent interest, particularly to the description of the triangular silver particles.Preparation and Characteristics of SERS-Active Substrates.We employed molecular spectroscopy to study the fabrication process of SERS substrates. Our purpose is to explore the relationship of the nanoparticles' structures and spectra. Three novel methods were developed, (a) The small silver nanoparticles were used as the crystal seeds to prepare the SERS substrate, (b) Various lights were employed to induce the triangle silver nanoparticles formation in solution, (c)...
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