Research On Manufacture And Sers Of Vertically Coupled Metal Micro-nano Structures

Strong local electromagnetic field arises near the metal nanostructure from the surface plasmon resonance of metal nanostructure,and can excite Raman spectra of probe molecules efficiently.Moreover metal nanostructure can provide optical antenna effect,enhance the interaction between light and matter,realize interconversion between localized field and free propagating optical field,and thereby has been widely applied to regulation of light,enhancement of fluorescence and Raman,near-field optical image and so on.In this dissertation,based on the characteristics of modes,coupling properties and regulation of electromagnetic fields and luminescence of metal micro-nano structure,using Ag triangle-gap-Ag film vertically coupled structure as the basic structure,we design and fabricate three kinds of vertically coupled metal micro-nano structures which support for multiple modes,and can be easily realized and used as surface enhanced Raman scattering(SERS)substrates.The SERS signals enhanced by coupled metal micro-nano structure and the characters of modes of the micro-nano structure are investigated by theoretical simulations and experiment.The relations between Raman signals,the characters of modes and the key parameters of the structures are discussed.Our works have important significance in analyzing the characteristics of modes controlled by the parameters of the structures deeply,broadening the new applications of the structure,further understanding SERS enhancement mechanism,designing low cost and high sensitivity new SERS chips etc.The main conclusions of the dissertation are shown as following1.Gap plasmon polaritons(GPP)between layers of film,localized surface plasmon(LSP)and optical antenna effect of the corners and edges of metal nanostructure,characteristics of coupling transformation,and possible application of SERS are introduced in designing structures.The micrometer-sized Ag triangular nanoplates are synthesized by chemical method,which have excellent smooth surfaces and sharp corners,can provide anisotropic spatial and micro-nano scale characteristics,and can support the two basic modes of surface plasmon polariton(SPP)and LSP.Hereby,we fabricate a vertically coupled structure composed of Ag triangle nanoplate on Ag film separated by dielectric film.We investigate the vertically coupled characteristics and the physics of enhanced SERS of single triangle nanoplate coupled with Ag film,using SERS spectrum measured by confocal scanning optical microscopy.The micrometer-sized Ag triangular nanoplates can not enhance Raman spectra,however the Ag triangular nanoplate coupled with Ag film with nanoscale gap size can dramatically enhance SERS by visible laser excitation.And we find that the Raman intensity is exponential dependence on the gap distance.The characters of Raman spectra are investigated excited from different sites of Ag triangle nanoplate,and compared with theoretical simulations.We find that the GPP between the Ag triangle nanoplate and the Ag film,and the LSP and the antenna effect of the edges and corners of the triangle nanoplate are the physical foundation of enhanced Raman scattering.And the vertically coupled structure is an efficient SERS substrate.2.Based on the above research,we present a large area vertically coupled nanostructure composed of uniformly ordered Ag triangle array on flat Ag film(Ag grating),considering the Raman signals enhanced simultaneously by excitation and radiation in broadband.Using monolayer packed closely polystyrene(PS)microspheres as the model,we fabricate a vertically coupled nanostructure with multiple control parameters and excellent properties by the nanosphere lithography technique incorporated with film layer control technology.The relations between the Raman intensities and the thickness of Ag film and gap,height of the Ag triangles,Ag grating period and the power of exciting laser are investigated by experiments and simulations.By optimal parameter of the nanostructure,the SERS substrate has 5.8×106 Raman enhancement factor and less than 4%relative standard deviation of reproducibility.The coupled structure has broadband absorption in the visible region,so both the exciting and the Raman light are enhanced which resulting in strong Raman signals.And the coupled structure is superior to the demands for the practical SERS substrate.3.In order to achieve superior performance,stable signal and practical SERS substrate,we present a large area,Quasi-3D SERS substrate of Ag film covering free-standing Ag triangle array,based on the above research.The large area,Quasi-3D vertically coupled nanostructure is fabricated by nanosphere lithography incorporated with photolithography and Ag covering.The gap distance between the triangle and the baseplate is well controlled by the thickness of Ag film covering.The relations between the SERS intensities and the thickness of Ag film covering are investigated from experiments and simulations.And when the thickness of Ag film covering is equal to the height of the photoresist pillar,the structure exhibits the best Raman enhancement effect,and obvious Raman signals can be observed at 10-7M concentration.Because the gap of the SERS substrate is an air layer,Raman molecule can be added into the gap according to different research purpose,which improve the application flexibility of the SERS substrateThe innovations of the dissertation are shown as following1.We fabricate a vertically coupled structure composed of isolated Ag triangle nanoplate on Ag film based on GPP between layers of film,LSP and optical antenna effect of the corners and edges of metal nanostructure,and characteristics of coupling transformation.And the mode properties of the coupled nanostructure are analyzed.The vertically coupled structure can dramatically enhance SERS by visible laser excitation,and thus confirms the structure is an efficient SERS substrate.The SERS substrate breakthroughs the restriction on the size of nanostructure,and expands the freedom of the SERS exciting wavelength.2.Considering the Raman signals enhanced simultaneously by excitation and radiation in broadband,we design and fabricate a large area vertically coupled nanostructure composed of uniformly ordered Ag triangle array on Ag baseplate by the nano sphere lithography technique incorporated with film layer control technology.By optimal parameter of the nanostructure,the SERS substrate has 5.8×106 Raman enhancement factor and less than 4%relative standard deviation of reproducibility,which provide reference to design low cost and high sensitive SERS chips.3.We design and fabricate successfully a practical large area,Quasi-3D SERS substrate of Ag film covering free-standing Ag triangle array by the nanosphere lithography technique incorporated with film layer control technology,using monolayer packed closely PS microspheres as the model.Benefiting from the high density hot spot between the Ag triangle and the baseplate,the vertically coupled sructure can show obvious Raman signals at 10-7M concentration.Meanwhile,because the gap of the nanostructure is an air layer,Raman molecule can be added into the gap easily according to different research purpose,and thus the practicality of the SERS substrate is improved.