Study On The Local Field Enhancement Characteristics Of Surface Plasmon Nanostructure

Under the excitation of the incident electromagnetic wave,the interaction between the electromagnetic wave and the free electrons on the surface of surface plasmon?SP?nanostructure will form a resonant mode,thus changing the distribution of the local electromagnetic field on the surface of the SP nanostructure.It can realize the nanoscale regulation of photon state.When the frequency of the incident electromagnetic wave is the same as the free electron frequency of the nanostructure,the localized electromagnetic field can be greatly enhanced in the optical near-field range of the surface.Many novel optical phenomena,such as near-field enhancement,surface electromagnetic localization and non linear enhancement,will be revealed when the SP nanostructure resonate.It can be widely uesd in many fields such as surface-enhanced Raman scattering?SERS?spectrum,surface-enhanced fluorecence spectrum,solar cell,biosensor and light absorption enhancement.However,the resonance frequency of the SP is strongly dependent on the morphology,geometric size and the dielectric environment of the SP nanostructures,especially on the nanoparticles with tip structures.Because of its“hot spots”effect at the tip,it can significantly enhance the local effect of light at the nanometer scale,and increase the electric magnetic field intensity of the“hot spots”region by several orders of magnitude.It provides a new technical for the development of surface-enhanced spectroscopy under local field,and has gradually become the focus of research in the field of SP.The purpose of this thesis is to explore the local field enhancement mechanism,optimization design and fabrication process of multi-tip SP nanostructures.On this basis,nanostructures with“hot spots”effect were prepared and their local enhancement properties and applications were studied.How to improve the distance and efficiency of the surface enhanced change and energy transfer on the surface of the SP nanostructures by using the mechanism of the localized surface plasmon resonance?LSPR?enhancement is analyzed in depth.And the influence of“hot spots”effect on fluorescence resonance energy transfer in different tip nanostructures,thus revealing the resonance energy transfer mechanism in which nanostructures participate.It provides a theoretical and experimental basis for the future development of surface-enhanced spectroscopy devices based on a novel SP nanostructure substrate,and studies its application in photovoltaic enhancement by using the antenna convergence of nanostructures.The main research work are listed as follows,?1?In the design and optimization of multi-tip metal nanostructures.The influence of the morphology of metal nanoparticles?MNPs?and the coupling effect between them on the surface electric field intensity was simulated by finite element method.The electric field distribution of four silver nanoparticles with different curvature radius was studied.The relationship between the tip morphology of MNPs and the local field enhancement properties was obtaind.On this basis,we have designed a multi-tip gold nanostar?GNS?SP nanostructures.The influence of structure parameters such as the morphology of metal nanostructures,the size of GNS particles,the gap and the number of GNS particles on their optical propreties was studied.The intensity of“hot spots”and the position of resonance peaks in GNS particles were regulated.It provides theoretical guidance for experimental preparation and application of multi-tip GNS particles in later stage.?2?The SERS properties of GNS particles“hot spot”substrate were studied.In the experiment,the multi-tip nanostructures were prepared by seed growth method,and the yield of the GNS particles reached nearly 100%.The growth mechanism of GNS particle tip was discussed,and the control of GNS particle tip morphology was realized.For the first time,an assistant-free self-assembly technique was proposed to prepare the GNS particle SERS substrate.The shell layer on the surface of the SERS substrate was removed by the acetone soaking method to suppress the fluorescence background in the SERS signal detection,improving the SERS signal.By accurately controlling the distance between the analyte and the GNS particles,the energy transfer characteristics of the analyte on the surface of the MNPs are affected,and the fluorescence quenching of the analyte results in the enhancement of the SERS signal.The competition relationship between fluorescence background and SERS signal caused by shell layer is explained theoretically.It also provides a way for us to study the surface enhanced fluorescence properties based on the GNS particles.?3?Fluorescence enhancement of GNS@SiO₂ core-shell nanostructure.A novel GNS@SiO₂@CdSe/ZnS quantum dots?QDs?nanocomposite structure has been developed experimentally.The distance between the surface of the metal nanostructure and the CdSe/ZnS QDs is effectively controlled by the SiO₂ thickness of the shell.Then,with the help of the“hot spot”characteristic of multi-tip GNS particles,the method of enhancing fluorescence effect and the corresponding new metal nanostructure system are found.Surface enhanced fluorescence resonance energy transfer efficiency was improved,which revealed the fluorescence enhancement mechanism between GNS particles and CdSe/ZnS QDs.?4?Study on photovoltaic efficiency characterisitics of metal nanostructrres inlocal field.Based on the antenna convergence characteristics of metal nanoparticles?MNPs?,the effect of MNPs embedded in different functional layers?photovoltaic and buffer layer?of organic solar cells is analyzed in depth,and the position of MNPs embedded in the cells is determined.The law of the light absorption performance of the cells enhanced by embedded MNPs with different shapes in the functional layer was discussed,and the optimized design method of the MNPs structure parameters was established based on the theoretical model.The effects of four kinds of MNPs with different curvature radiuses on the light absorption characteristics of the cells were studied,obtaining the maximum light absorption enhancement of 1.19 times.