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Studies of Design and Enhancement Mechanism of Resonance SERS Substrates

Author: ZhouYing
Tutor: YangLiangBao;ZhangLi
School: Anhui University
Course: Inorganic Chemistry
Keywords: Surface-enhanced Raman scattering Local surface plasmon resonance surface plasmon resonance Surface-enhanced resonance Raman scattering doubleresonance
CLC: O657.37
Type: Master's thesis
Year: 2014
Downloads: 4
Quote: 0
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Abstract


Surface-enhanced Raman spectroscopy technology (SERS) has become an important analysis technique due to its high sensitivity. At present, the SERS active substrates mainly confined to some researches of noble metals and transition metals, many people obtain good SERS effect via regulating the structure and morphology of nanomaterials. While in this article we study the SERS enhancement mechanism, based on electronic absorption spectra of the compound or nanoparticle substrate resonantly coupling with the incident light energy and the LSPR of nanoparticles coupling with the SPR of grating effect of resonance. Then the resonance SERS substrates with high efficiency and higher SERS enhancement effects are obtained. The main summaries are as follows:(1) After the reaction of1,10-phenanthroline (phen) and Fe2+, a stable orange-red complex (phen-Fe2+) is formed, the absorption band is at510nm, it overlaps with Ag nanoparticles LSPR absorption and resonantly couples with incident light energy. Based on these two points, this chromophore absorbs the visible light that matches with the incident laser and plasmon resonance of Ag sols by the use of a532.06nm laser, and offered large resonance Raman enhancement. The detection limit of phen-Fe2+reaches as low as to10-13M. Then the study of the selective detection of Fe2+is conducted, the experimental results show that only the Fe2+can form effective charge transfer chromophores complexes to cause the Raman enhancement of phen, the selective testing purposes of Fe2+is achieved.(2) Based on the fact that the nanoparticle-film coupling systems that metal nanoparticles (supported localized surface plasmons LSPs) separated from a flat metal film (supported surface plasmon polaritons SPPs) by a spacer has strong local enhancement field, we propose and fabricate a novel double-resonance SERS system through strategically assembling Au NPs spaced by MoO3nanospacer from an Ag grating film. It is the first time to use the Ag grating which shows clear SPP effect in the double-resonance system and the monolayer Au NPs array is well assembled onto the top of the Ag grating with compact and uniform distribution (inter-particles gap about5nm). As a result, we experimentally and theoretically demonstrate a significant near-field enhancement. The very strong near-field produced in the proposed SERS substrates is due to multiple couplings including the Au NPs-Ag grating film coupling and Au NPs-Au NPs coupling, the largest SERS EF is measured to be2.47×107.(3) Because of the limitation of SERS sensitivity of Au NPs, we demonstrate a different means to achieve double resonances by use of silver nanoparticle as the enhanced substrate. The assembly method of Ag NPs is easy to realize. Now that Ag provides a higher SERS enhancement efficiency than Au, it is natural to expected that Ag NP/MoO3/Ag grating substrate can achieve a higher SERS enhancement than Au NP/MoO3/Ag grating substrate. In this work, SERS spectra of crystal violet (CV) molecules adsorbed on double-resonance substrates with different dielectric thicknesses are used to investigate the SERS application. The SERS enhancement factor for the double-resonance structure is found to be more than8times larger than that of a regular Ag nanoparticles array on a silicon substrate and the double resonance structure with optimal array dielectric thickness produces considerably higher SERS EF than the structures with nonoptimal dielectric. The largest SERS EF for the1620cm-1Raman line of the CV molecule is measured to be2.65×108.Through above studies, we prepare the novel resonant SERS substrate with good effect, push the in-depth application of SERS method in analytical chemistry and the field of environmental detection and extend the SERS substrate preparation method.

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CLC: > Mathematical sciences and chemical > Chemistry > Analytical Chemistry > Instrument analysis ( physics and physical chemistry ) > Photochemical analysis ( spectral analysis method) > Raman spectrometry
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