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Surface-enhanced Spectroscopies Study Of Gold And Silver Nanoparticles

Posted on:2006-07-14Degree:MasterType:Thesis
Country:ChinaCandidate:Y ZhuangFull Text:PDF
GTID:2121360155967409Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Metal nanoparticles (mainly gold, silver and copper) have been the subjects of a numbers of studies for fundamental interests and practical applications, due to that the optical properties of metal nanoparticles are strongly dependent on the size, shape and environment of the particles. Under irradiation of lights with a proper wavelength, the surface plasmon in metal particles can be excited, as a result, the local electric field close to the particles can be greatly enhanced. This is the foundation of various spectroscopic techniques sensitive to the electromagnetic fields, particularly of surface-enhanced Raman spectroscopy (SERS), surface-enhanced fluorescence spectroscopy (SEF). Recently, these methods have been used to inspect the signs of single molecules. Understanding of optical properties of metal nanoparticles is therefore extremely important. The present research works have been focused on the following issues: the contribution of charge transfer (CT) mechanism to surface-enhanced Raman scattering (SERS) and the effect of metal nanoparticles on the fluorescence of neighboring molecules. First, the SERS spectra of p-aminothiophenol were investigated on silver and gold nanoparticles. It was found that charge transfer from metal to the surface-adsorbed molecules is more favorable on the silver nanoparticles than that on the gold nanoparticles. This is attributed to the fact that the work function of gold is larger than that of silver. Besides, the charge transfer process is also influenced by surface property and architecture of nanoparticles, and coadsorbed anions on surface. Second, Ag/SiO2 core-shell nanoparticles were prepared by surface modification of silver nanoparticles. It was found that the surface plasmon resonance of the silver core can be altered by the thickness of the SiO2 shell, a red shift of the absorption band of the silver core was observed with increasing of the shell thickness. The fluorescence of Rhodamine 6G was largely enhanced in the presence of the Ag/SiO2 nanoparticles, and the enhancement was largely dependent on the thickness of the SiO2 shell. Optical properties of Rhodamine 6G (R6G) and fluorescein (FL) were also studies in the presence of gold nanoparticles. The nonradiative energy decay and unfavorable orientation of R6G to gold nanoparticles led to a decrease in the intensity of the emission of R6G. . In contrary, the emission intensity of FL was substantially increased in thepresence of the gold nanoparticles, due to the necessary space generated by the electrostatic repulsion between FL molecules and the citrate-passivated gold nanoparticles. In the case of Rhodamin B, it was also found that "hot spot" produced by aggregation of gold nanoparticles is responsible for the enormous enhancement of the fluorescence of the dye molecule.
Keywords/Search Tags:Surface-enhanced Raman spectroscopy, Surface-enhanced fluorescence spectroscopy, Nanoparticles, Dye, Charge transfer.
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