Investigation Of The "Hot Spots" Effect On Multi-Dimensional Metallic Nanostructures

Normally,surface-enhanced Raman spectroscopy(SERS)is mainly contributed by the "hot spots" effect The SERS activity of "hot spots" is critically dependent on the material nature,morphology,size,aggregation state and laser wavelength.The small changes can lead to significant differences in SERS activity,besides,"hot spots"are usually randomly distributed on the metallic nanostructures.Therefore,it is of great significance to investigate the "hot spots5" effect both for the further understanding of SERS enhancement mechanisms and the guidance of fabrication on SERS substrates.At present,the investigation on the "hot spots" effect is mainly based on theoretical simulation and simple experimental models,such as a nanoparticle dimer.However,little attention has been paid to the SERS substrates with practical applications.The main reason is that it is difficult to construct a suitable coupled model with great uniformity and sensitivity,which brought the lack of comparability of SERS intensities from different spots or substrates.In this thesis,combined with the probe molecular strategy,several kinds of metal nanoparticles films coupled with Au single crystal plates were constructed to investigate the "hot spots" effect.The main results were listed as follows:(1)Developed a dual-probes strategy for investigating the "hot spots" effect.Au nanoparticles mono-/bi-layer films coupled with Au single crystal plates were constructed to investigate the wavelength dependence of the "hot spots",effect based on the experimental and theoretical simulation.The transfer of "hot spots" from"particle-particle" mode to "particle-surface" mode was preferred with 638 nm laser for Au monolayer film-Au plate coupled system,while it disappeared on the naked Si substrate without Au plate.As the second layer of naked Au monolayer film was transferred onto the first Au nanoparticles monolayer film,"hot spots" was transferred to the "particle-particle" gap area between the upper and lower Au nanoparticles films with 638 nm laser as excitation line.(2)Au@Ag nanoparticles mono-/bi-layer films coupled with Au single crystal plates were constructed to investigate the "hot spots" distribution and the electromagnetic field enhancement.The 638 nm and 532 nm laser were well matched with the "particle-surface" coupling mode and "particle-particle" coupling mode,respectively.The introduction of the second layer of Au@Ag film resulted in the change of the local distribution of the electric field,which was critically relevant to the laser wavelength.Moreover,the upper naked Au@Ag film played the similar role as the Au plate in this case.(3)Surface plasmon catalytic coupling reactions of PATP and PNTP were utilized to investigate the "hot spots" effect of Au and Au@Ag nanoparticles mono-/bi-layer films.The results revealed that the catalytic efficiency was related with the laser wavelength and material nature in the following sequence 638 nm>785 nm for Au substrate and 532 nm>638 nm>785 nm for Au@Ag substrate,and it was independent with the number of nanoparticle monolayers.For bilayer films,the transfer of "hot spots"from intralayer "particle-particle" mode to interlayer "particle-particle" mode was preferred with 638 nm laser for both Au and Au@Ag substratesThis research provides the experimental basis for the design of well-performed SERS substrates and optimizing the detection of SERS signals at specific surfaces.It also provides the suitable model systems for the investigation of enhancement mechanisms.It is beneficial to the development of theoretical simulation and practical applications of SERS.