Research On Surface-enhanced Raman Scattering Substrates Based On Composite Materials

Surface-enhanced Raman scattering(SERS)is an optical phenomenon.When molecules are adsorbed on a surface of rough metal(such as gold,silver,copper,etc.)nanostructure,its Raman scattering signal is greatly enhanced under light.SERS technology,which has some advantages such as high sensitivity,low detection limit and good selectivity,has great development potential in environmental protection,food industry,medical detection,biological detection and other fields.For SERS technology,SERS substrate plays an important role,and the enhancement effect of Raman scattering signal mainly depends on the material and structure of SERS substrate.The SERS substrate made of single noble metal material has good enhancement ability,but there are some problems such as high cost,easy oxidation and poor repeatability.The SERS substrate made of semiconductor material has low cost and high stability,but the enhancement effect is not ideal.The research on SERS substrate made of noble metal/semiconductor composite material is expected to solve some problems,such as high cost,easy oxidation,poor repeatability and low sensitivity.This thesis carries out a research on SERS substrates made of composite material,and design three new types of SERS substrates made of precious metal/semiconductor composite materials.The Finite-Difference Time-Domain(FDTD)method was used to simulate and analyze the local electromagnetic field,extinction spectrum and SERS characteristics.A higher enhancement factor was obtained by optimizing the structural parameters of the SEES substrate.The main research contents are as follows:(1)Research on SERS substrates made of different semiconductor films modified by spherical Ag nanoparticlesA SERS substrate,which is consisted of Ag nanoparticles(Ag NPs)and semiconductor film,and the semiconductor film is modified by Ag NPs,was designed.The semiconductor material was Ge or Si,Ga As and In As,respectively.Based on the electromagnetic field theory,the extinction spectrum and local electromagnetic field of SERS substrate was simulated and analyzed by using FDTD method.Firstly,the influence of the radius of Ag NPs and the thickness of Ge film on SERS substrate was discussed,and then the influence of different semiconductor films on the enhancement ability of SERS substrate was discussed.By optimizing the structural parameters and calculating the enhancement factor,it was found that the SERS substrate of Ag NPs/Ge film with radius of 50 nm and thickness of 10 nm produced a stronger electromagnetic field under the excitation of incident light at 633 nm.The enhancement factor is up to 7.02×10~7.The substrate of Ag NPs/Ge film has better enhancement effect for Raman scattering signal.(2)Research on SERS substrates made of Ag NPs arranged in different ways on Ge filmWe arranged Ag NPs as a ring and a chain on Ge film respectively to form two Ag/Ge composite metaerial SERS substrate,respectively.Based on the Electromagnetic field theory,the local electromagnetic field and extinction spectrum of this two type SERS substrates were simulated and analyzed by using FDTD method.The enhancement effect on Raman scattering signal of this two type SERS substrates was discussed.By optimizing the structural parameters and calculating the enhancement factor,it was found that when the spacing of Ag NPs was the same,compared with the ring arrangement,the SERS substrate of Ag/Ge composite with chain arrangement of Ag NPs produced stronger electromagnetic field under the excitation of633 nm incident light,with the enhancement factor up to 3.0×10~7.It has better Raman scattering signal enhancement ability.(3)Research on SERS substrate made of columnar Ag/Ge composite materialA SERS substrate composed of Ag nanocolumn and Ge film was designed.Based on the electromagnetic field theory,the local electromagnetic fields of SERS substrates of Ag/Ge composites with cylindrical,quadrangial and triangular shapes of Ag nanocolumns were simulated and analyzed by FDTD method.The effects of the shape,height and spacing of adjacent nanocolumns on the enhancement ability of SERS substrates of Ag/Ge composite were discussed.It was found that the shape of Ag nanocrystals is triangular prism,the nanocolumn height is 200 nm,and the nanocolumn spacing is 8 nm,the SERS substrate of Ag/Ge composite material could generate a strong electromagnetic field with the enhancement factor up to 8.35×10~8under the ncident light excitation with wavelength 633 nm.The SERS substrate has a good enhancement effect on Raman scattering signal.The research on SERS substrate based on composite materials carried out in this thesis is expected to provide a new theoretical support for the design and research of new SERS substrate with excellent performance.