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Study Of Surface-Enhanced Raman Spectroscopy And UV Raman Spectroscopy

Posted on:2003-03-27Degree:MasterType:Thesis
Country:ChinaCandidate:E Z TanFull Text:PDF
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Surface-enhanced Raman Spectroscopy (SERS), a highly sensitive technique for studying the vibration spectra of molecules, has been extensively used in biology, physics, chemical industry and material, etc. Metal colloids are used usually as one kind of SERS substrates. Colloids preparation, as well as the study of their optic characters and shapes, plays an important role in SERS study. Ultraviolet (UV) Raman also draws much attention because of a number of advantages. We focus on several aspects mentioned above in this thesis, which includes three parts: the synthesis of metal colloids, their absorption spectra, their shape characters and Raman activity; the influence of halogen ions on SERS of aromatic carboxylic acids; UV Raman of aromatic carboxylic acids.SERS of metal colloids is discussed in the first part of this thesis. We analyze the optical absorption spectra, the transmission electron microscope (TEM) images of the colloidal silver and gold. We record the overall spectra of them, from UV to near-infrared (NIR) band, in order to understand the dependence of enhancement on exciting wavelength. We compare the achieved results with those from theory calculation. We improve the theory to make it fit the experiment results better. We also prepare two kinds of mixture colloids, Ag-coated Au and Au-coated Ag colloids. We study them by the methods mentioned above and find that it makes the enhancement of Au SERS better by depositing Au on performed Ag colloid particles.The influence of halogen ions on SERS of aromatic carboxylic acids is discussed in the second part. The SERS signal is usually enhanced when chlorine ions are added to the adsorbate-Ag colloids system as in the experiments done before. Most accepted explanation to this is that chlorine ions speed the aggregation of colloids. However, we find the opposite changes in SERS of aromatic carboxylic acids adsorbed on colloidal silver caused by adding halogen ions. Our interpretation is that the acid molecules fall from the silver surface when the halogen ions are adsorbed there. We also observe that scattering background of the aromatic carboxylic acids-halogen ion-colloids system falls, like the Raman signal, when the exciting light wavelength is 514.5nm. Whereas abnormal changes take place with a 1064nm exciting light: the scattering background rises when the Raman signal lowers. We explain this in that the system has different response to light of different wavelength.UV Raman spectra of aromatic carboxylic acids solution is discussed in the third part. We compare these with visible and NIR Raman spectra of their solids as well as SERS of their solutions. The sensitivity of UV Raman is at least 102-fold higher than visible and NIR Raman because of high frequency of UV and resonance enhancement.
Keywords/Search Tags:Surface-enhanced Raman Spectroscopy, optical absorption, silver colloids, mixture colloids, p-hydroxybenzoic acid, UV Raman Spectroscopy
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