Mercaptoacetic acid-capped spherical silver nanoparticles with a diameter of about 17nmwere prepared by a simple chemical reaction. The formation process of the silver nanoparticles was investigated by UV-visible(UV-vis) spectroscopyandtransmission electron microscopy.Theresultsshowthat 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

In this paper, we propose two new approaches for preparing active substrates for surface-enhanced Raman scattering (SERS). 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 Agnanoparticles on the substrate. The second approach (method 2) deoxidizes AgI to Agnanoparticles in a colloid solution and then transfers the Ag nanoparticles capped by negatively charged mercaptoacetic acid onto a quartz slide. By transfer of the AgI/Ag nanoparticles from the colloid solutions to the solid substrates, the problem of instability of the colloid solutions can largely be overcome. The films thus prepared by both approaches retain the merits of metal colloid solutions while they discharge their shortcomings. Accordingly, the obtained Ag particle films are very suitable as SERS active substrates. SERS active substrates with different coverages can be formed in a layer-by-layer electrostatic assembly by exposing positively charged surfaces to the colloid solutions containing oppositely charged AgI/Ag nanoparticles. The SERS active substrates fabricated by the two novel methods have been characterized by means of atomic force microscopy (AFM) and ultraviolet-visible (UV-vis) spectroscopy. The results of AFM and UV-vis spectroscopy show that the Ag nanoparticles grow with the increase in the number of coverage and that most of them remain isolated even at high coverages. Consequently, the surface optical properties are dominated by the absorption due to the isolated Ag nanoparticles. The relationship between SERS intensity and surface morphology of the new active substrates has been investigated for Rhodamine 6G (R6G) adsorbed on them. It has been found that the SERS enhancement depends on the size and aggregation of the Ag particles on the substrates. Especially, we can obtain a stronger SERS signal from the substrate prepared by method 1, implying that for the metal nanoparticles capped with stabilizer molecules such as mercaptoacetic acid, the in situ deoxidization in the film is of great use in preparing SERS active substrates. Furthermore, we have found that the addition of Cl

Near-infrared surface-enhanced Raman spectroscopy was applied to the investigation of 4, 4′-bipyridine, 4, 4′-azopyridine, bissalicy-laldehydeethylenediimine Co (II). and Ni (II). abbreviated as Salen-Co and Salen-Ni, respectively. as mono- and alternating multi-layer self-assembly films deposited onto the roughened silver foil substrate. 4, 4′-Bipyridine, 4, 4′-azopyridine can be adsorbed onto the silver substrate through the interaction of N-atom of the pyridine ring via metal surface. The orientation of molecular long axis for both molecules are normal to the surface of the substrate. The alternating films can be obtained by the coordinate interaction between the pyridine and the metal chelates of Salen-Co and Salen-Ni. The plane of the metal chelates are parallel to the surface of silver substrate. © 1999 Elsevier Science S.A. All rights reserved.

Silver colloids are one of the extensively employed surface-enhanced Raman scattering (SERS) active substrates. To obtain the SERS effect, their aggregation upon addition of analyte is necessary. However, problems of instability and irreproducibility in the magnitude of the signal are caused by the formation of aggregates. Considering that the aggregation of silver colloids is essential to induce small silver clusters, in the present study, we develop a drying process to prepare silver particle films (silver clusters) that are supported directly on a glass slide. These silver particle films arise through the aggregation of silver colloids occurring in thin water films supported on a solid substrate. With the evaporation of water, silver clusters are left on the solid substrate. Thus, the assembly meets perfectly the requirement of aggregation of silver colloids and, at the same time, possesses the stability of solidlike SERS-active substrates. We can easily obtain excellent SERS spectra from these silver particle films. These substrates show great potential in practical applications such as ultrasensitive microanalysis with micro-Raman spectroscopy and are suitable for studying the optical properties of silver clusters. 4-Mercaptopyridine (4MPY) was used to test the utility of the proposed method and to compare it with the chemically deposited silver film (silver mirror) method. The intensity of SERS signals of 4MPY on the silver particle films is stronger by about 100 times than that of 4MPY on the silver mirror. In addition, the experimental results of SERS reveal that the activation agent, coadsorbed chloride ions, can further enhance the SERS signals from both the silver mirror and the silver colloids.