Control And Application Of Plasmonic Resonance In Metallic Arrays

During the last several decades,surface enhanced Raman scattering(SERS)has become an important molecular detection technology,widely used in the field of spectral analysis.This attributed to the tremendous enhancement of Raman signals on plasmonic nanostructured surfaces.Generally,the well-recognized requirements are the high sensitivity and the great uniformity for super performance of SERS substrate.High sensitivity of Raman signal is derived from powerful hotspots by tuning nano particle size,shape,and spacing between two particles.On the other hand,the enhancement effect of SERS substrate should be consistent at various test areas.The common preparation methods for SERS substrate include bottom-up methods and top-down methods.Hoever,it is difficult to fabricate large area uniform array with less than 10 nm spacing by means of the existing fabrication methods,resulting in hardly achieving high sensitivity and good repeatability of substrate for surface enhanced Raman scattering so far.The purpose of this paper is to improve the nanofabrication method,to fabricate nano metallic structure with large area,high density and small spacing,to develop uniform surface plasmonic enhanced electric fields,and to explore the applications in the field of spectral enhancement.We focus on using lithography to develop a novel sandwich structure.The main contributions in this dissertation are summarized as follows:(1)By using electron beam lithography,variety of sizes,shapes and configurations of the arrays were fabricated.Synchrotron radiation X-ray interference lithography was also used to fabricated rapidly metallic arrays with large area and small period,which were applied to detect R6 G molecular based on surface enhanced Raman scattering.Results show that the substrate has good sensitivity,high uniformity and repeatability,showing promising potential to commercial application.(2)In this work,we report an array–film(AF)nanofabrication approach that combines EBL and sputtering deposition to deterministically create plasmonic nanostructures with tunable below 10 nm gap and uniform periodic nanodisc arrays.As a result,compared with a reference gold(Au)array on a silica(SiO2)substrate,the AF hybrid SERS substrate exhibits dramatic enhancement of the Raman signal towards rhodamine 6G by one order under the same measurement conditions.(3)With the limit of a few nanometers insulation layer,Raman signal is also very sensitive to the size of gold nanoparticles and the thickness of SiO2 separation.The SERS performance of the AF substrate can be easily tuned by changing the thickness of SiO2 separation.(4)In this work,we study the multiple resonance modes in the sandwich structure theoretically and experimentally.Theoretical results show that the optical excitation and interference excited by the incident light in sandwich structure.With the spread on metal surface,plasmon resonance modes in the structure are limited at the top of gold nanoparticles and in the insulation layer under the nanodisc.(5)The sandwich structure can theoretically equivalent to the Fabry Perot cavity,and the diameter of nano disk can be regarded as the length of Fabry Perot cavity.With the changing of the cavity length,new resonant modes can be excited resonance at multi wavelength.The results show that the multi wavelength resonance in the only one sandwich structure can achieve the best results under three incident excitation.And the structure can be applied to SERS detection under multi-wavelength.