Two-dimensional Assembly Of Silver Nanoparticles And Its Application In Surface-enhanced Raman Spectroscopy

With the rapid development of nano-meter science, nano-particies of metals ,having particular properties, have been employed in various research areas. Meanwhile, some new fields such as nano-physics, nano-chemistry, nano-material and nano-electronics have become quite active fronts of investigative directions. Nano-particle of metal has many unique physical and chemical properties. It is an effective approach to make the nano- particles in an ordered structure for better investigations of these phenomena. By preparing steady metal sd of gold or silver with different size and even granularity, developing a technology for making nano-particle array with good repetition in a strongly controlled manner, suitable metal nano-particle assembled array electrodes can be fabricated and applied to electrochemistry and biochemistry. Furthermore, researches of surface-enhanced Raman scattering (SERS) of nano-particle arrays add new contains for mechanism of electrochemistry and SERS, and exploit new tract for single molecule detection. FT-Ranian spectroscopy plays an important role in microanalysis, due to its good test capability and wide spectral scale. It has notable superiority in eliminating fluorescence. Because a 1064 nm excitation is used, molecule fluorescence can not be excited in most cases, thus avoids the interference of fluorescence in Ranian spectra. In this dissertation, FT-Ranian spectroscopy was used to compare the surface properties of the metal nano- particle arrays and an ORC roughened electrode. The following research works have been presented: 1. By preparing steady, even granularity silver sol, we investigated thennodynamics, stabilization of metal nano-particles assembled on different substrates with different coupling reagents. Absorption spectra and SEM indicate distribution of the particles is uniform in a two-dimensional array structure- all particles are of the same size and dimensions, which is very important in SERS because Raman enhancement at the surface is directly correlated to nanometer scale roughness. Besides, strong covalent or non- covalent bonds to the substrate reduce the surface mobility of the nanoparticles and prevent the spontaneous coalescence of particles on the surface. Thus, the initial size uniformity is maintained. Iv ABSTRACT ~z~cm~ 2. The adsorption behavior of methylviologen (MV) on ORC roughened Ag electrode (RAg) and nanoparticle array (AAgNP/ITO) have been studied utilizing the electrochemistry and FT-SERS techniques. The observations strongly suggest that the adsorbed MV likely adopted a parallel orientation to the RAg electrode surface. Very weak SERS bands were observed on the surface of AAgNP/ITO,which may result from MV adsorbed on the aggregate of Ag particles .Thus, the surface defects andlor aggregates of Ag nanoparticles are essential for the adsorption of MV, while the isolated silver particle may not possess the necessary active sites for parallel adsorption of MV molecules. Electrolytes were found to have effect on Ranian intensity of adsorbed MV. For example, the presence of halide ions can increase Ag activity, and consequently enhance the interaction between Ag particles and MV. Due to the strong adsorption of halide ions on the silver electrode, the anions can compete with MV, leading to a intensity decrease of the signal with time. The experimental results also revealed that the SERS effect may result...