| When molecules are adsorbed on special metal surface, their Raman intensities can be increased by a factor of 104~106 compared with their normal spectra observed. This phenomenon is generally known as surface-enhanced Raman scattering (SERS). A number of chemists and physical scientists are very interested with the study on SERS which have been an active research field. However, the evolution of SERS-active substrates is the key role to initiate and /or broaden novel SERS applications. To make SERS become a usual analytical tool, developing stable and reproducibly prepared substrates with high enhancement become important. Therefore, the methods of preparing SERS substrates have long been a matter of great concerns and have become a crucial role in the development of SERS.Additionally, the study on ultrathin organic molecular films can not only help people to understand the fabrication of organic molecules in organism, but also help people to fabricate organic thin films with special functions. Consequently, people can construct molecular devices or supermolecular devices. For thin organic molecular film, its properties depend on its molecular structure and character. As a sensitive analytic tool, SERS have unique advantages in studying the structure and orientation of thin films. Thus, study on the self-assembled films by using spectroscopy can make people understand the relationship between the structure and properties of the thin films, which can help spread the application of such films in practice.Based on the above facts, our study is outlined as follows: 1. Mercaptoacetic Acid-Capped Silver Nanoparticles Colloid --- Formation, Morphology and SERS ActivityWe discuss the formation, morphology and SERS activity of the mercaptoacetic acid-capped silver nanoparticles colloid. The formation process of the silver nanoparticles was investigated by UV-vis spectroscopy and TEM. The results show that the spherical and rodlike particles were formed at the beginning of the reaction, and then the rodlike particles were gradually converted into spherical particles with the reaction continuing. Finally, the content of the rodlike particles was less than 3% in the silver colloid. Thus, the final obtained silver nanoparticles were uniform in their shapes and showed little variation in their sizes. This silver colloid can remain stable for several weeks, which makes it convenient for use in practice. We also investigated the effect of Cl- on the rate of changes in the optical properties of the silver colloid by UV-vis absorption. The results indicate that Cl- accelerates the aggregation of the colloidal particles by effectively screening the repulsive electrostatic interactions between the negatively charged silver particles. We used the self-assembled technique to transfer the silver nanoparticles onto solid substrates from the colloid with and without Cl- in the solution. The UV-vis spectra show that the absorption band red shifts and a new band appears at a longer wavelength when the silver nanoparticles are transferred onto the substrate from the colloid with Cl- in the solution, indicating that the silver nanoparticles can grow and aggregate on the substrate. This was further confirmed by the atomic force microscopy measurements. Both the silver colloid and the substrates prepared by transferring the silver nanoparticles from the silver colloidal solution onto the quartz slides can serve as SERS-active substrates. It was found that the SERS enhancement depends on the size and aggregation of the silver particles, and the addition of Cl- generates much stronger SERS signals.2. Self-Assembled Metal Colloid Films: Two Approaches for Preparing New SERS Active SubstratesWe report the two new approaches for preparing SERS-active substrates. In the first approach (Method 1) one transfers AgI nanoparticles capped by negatively charged mercaptoacetic acid from a AgI colloid solution onto a quartz slide and then deoxidizes AgI to Ag nanoparticles on the substrate. The second approach (Method 2) deox...
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