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Surface-enhanced Raman Study Of Molecules Adsorbed On Nanostructured Metal Surface

Posted on:2005-06-24Degree:MasterType:Thesis
Country:ChinaCandidate:Y JiFull Text:PDF
GTID:2121360125466339Subject:Physical chemistry
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Nanosized particles of metals, particularly silver and gold, have recently received increasing attention, due to their size, shape and environmental tunable optical and electrical properties. They have shown various potential applications in many fields, including nanodevices, nanocatalysis, biosensors and chemical sensors. For those applications, it is necessary to immobilize metal particles onto a solid substrate. Therefore, efforts have devoted to the assembly of nanoparticles in high ordered structures. Among various methods that used for the assembly of metal nanoparticles, self-assembly technique is one of the most flexible approaches for the immobilization of metal particles on substrates. In this thesis, we employed different methods to modify the surfaces substrates, including glass, silver and aluminum, and assembled silver and gold nanoparticles via electrostatic interaction and covalent bonding, the fundamental molecules for metal particle assembly were also studied by Surface-enhanced Raman spectroscopy (SERS).Silver nanoparticles were assembled on the surface of glass modified with polyvinylpyridine(PVP), forming two-dimensional submonolayer structure. The particles were uniformly distributed on the glass surface due to the electrostatic repulsion among the particles. The assembled silver particles showed quite different optical behavior from that of individual particles. Thus, blue shift of the dipolar resonance of silver particles was observed in the assembly, as compared to that of the particles in colloid. Dipolar coupling between particles was proposed to be responsible for the spectral change. Moreover, as a result, the dipolar resonance of the assembled silver particles depended on the incident angle of the lights.The interface acidity and complexation of Mercupotobenzoic acid (MBA), one of the most widely used molecules in surface modifications of metals as well as metal nanoparticle assembly, were investigated on electrochemically roughened silver electrode by SERS technique. The characteristic bands of MBA were identified as the pH sensitive indicators at the silver/water interface. It was demonstrated that SERS technique can beemployed for the titration of the surface bonded organic acid. Deprotonation of MBA can interact with the metal ions, such as Cu2+ and Cd2+, in aqueous solution to form surface complexes.The assembled silver nanoparticles on a smooth silver surface can enhance the Raman scattering of the coupled molecules, p-aminothiophenol (PATP). Such enhancement was even larger than that observed on electrochemically roughened silver electrode, which is the most widely used SERS substrate in various studies. The enhancement is related to the electromagnetic coupling of the localized surface plasmon resonance of silver metal particles and the surface polariton of the silver substrate. The assembled gold nanoparticles, on the other hand, showed relatively weak enhancement for the Raman scattering of the coupled PATP. This has been ascribed to the mismatching of the surface plasmon resonance of the gold particles with the surface polariton of the silver substrate. Aluminum, as a substrate, can induce the aggregation of the assembled silver nanoparticles, which, in turn, generate large surface bonded silver crystal. Both silver and gold particles on aluminum surface can enhance the Raman scattering of the coupled MBA molecules, which were chemically attached to the surfaces of the aluminum substrate and metal nanoparticles.
Keywords/Search Tags:Surface-enhanced Raman Spectroscopy, SERS, metal nanoparticles, Self-assembled monolayer, SAM.
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