The Study On The Structure,Plasmonic Resonance Modes And SERS Properties Of Metallic Nanoparticle Arrays Fabricated By Nanosphere Lithography

With the increasing advances in nano-fabrication techniques,various new type of metallic nanostructures have been designed and fabricated out,which exhibit rich and varied optical properties.In these optical properties,as a super-sensitive and nondestructive detection technology,surface enhanced Raman scattering(SERS)has been applied in various field,such as chemistry,biology,material science and medical detection,and is one of the hotspots in present academic researches in the world.In this thesis,we gave detailed studies on optical properties of the novel metallic nanostructures fabricated by nanosphere lithography(NSL).We experimentally explored how the surface plasmon(SP)properties and the SERS performances of the novel metallic nanostructures were influenced by their geometric parameters,and studied the relations between the SP mode and the SERS properties.The thesis is mainly composed of three sections that are arranged as following:1.The transmission,reflection,absorption spectra and the SERS performance of the noble metal half-shell arrays were researched.A general rule about the SERS intensities and the absorption properties of the substrates has been found.Using the NSL technology,we prepared a series of 2D ordered arrays of silver half shell by depositing a thin metal layer onto 2D colloidal crystal composed of polystyrene(PS)microspheres.The linear optical spectra and the SERS spectra of the half-shell array substrates with the different periods and the different silver deposition thicknesses were measured and analyzed.It was found that the optimized SERS-sustrate owned the optical quasi-perfect absorption band covering excitation and Stokes wavelengths.Further study revealed that under the mode of the dipolar plasmon resonance,the SERS intensity measured in the half-shell array substrates was proportional to the product of the absorptances at excitation and Stokes wavelengths.2.The absorption properties and the SERS performance of a hotspot-engineered quasi-3D metallic network with controllable nanogaps were researched.We found that the vast quality of sub-10 nn gaps in the metallic network brought better SERS performance.The metallic network was prepared by a combination of non-close-packed colloid monolayer templating and metal physical deposition.By precisely tuning the diameter of the PS microspheres through plasma etching and the quantity of silver deposition,the size of the nanogaps could be optimized to～10 nm,while a high optical absorption(over 90%)band of this metallic network spectrally covering the wavelengths of excitation laser and Raman band was still maintained.Through the optimization,under the 514 nm laser excitation,the Raman enhancement factor(EF)reached a large value of 1.5×108 and the detection concentration limit of Rhodamine 6G(R6G)was decreased to 1 nM due to the dramatically enhanced local electric fields in the sub-10 nm nanogap network,which was also verified by the numerical simulations.3.We studied how the geometric parameters of the metal triangle/insulator/metal(MIM)nanostructures affected their absorption properties and SERS performances,and analysed the physics mechanisms hehind the experiment.First,the MIM nanostructures consisting of the large area Au nanotriangles array on top of an optically opaque gold film separated by a silica layer was fabricated by NSL process.By optimizing the thickness of the silica layer,we got a broadband and polarization independent perfect absorber,whose absorption band could be tuned from visble to near infrared by controlling the size of the microsphere.In further SERS measurements,we found that the high optical absorption of the substrates benefited their SERS performances,and obtained the highest Raman EF as large as 4.9×106 with an improvement of 22 times increase compared to the same Au nanotriangles array deposited directly on a silica substrate.According to our numerical calculations,we found that the broad absorption band resulted from the generation of multi-plasmonic modes in the MIM nanostructure accompanying with the the enhancement of local electromagnetic field.Through controllable plasma etching process,the size of nanogaps of neighbouring Au nanotriangles was decreased to～10 nm,the Raman EF of MIM nanostructure was increased to 3.1×107 due to the dramatically enhanced local electric fields between the Au nanoparticles.Owing to the simple,productive,and inexpensive fabrication technique,above-mentioned metal nanostructures could be potential candidate for vaious applications such as SERS and solar cell.