Simulation Research On Raman Scattering Enhancement Characteristics Of Novel Tip-substrate Structure

Raman spectroscopy is widely used in nanomaterial molecular detection,and has made remarkable progress in non-destructive testing of composite materials and molecular imaging.High spatial resolution spectral imaging presents challenges due to the limitations of Raman scattering signals and optical diffraction limits.The TERS technology breaks through the weak limitations of Raman spectroscopy signals and enables the detection and structural characterization of nano-substance components.In this paper,the theoretical simulation analysis and experiment are carried out for the Raman enhancement effect of the new tip-substrate structure.Firstly,the TERS effect principle and evaluation method are theoretically studied,and the FDTD Solutions simulation analysis platform is determined.Secondly,a new concave tip and stepped tip structure are proposed.The influence of tip shape,material,Ag film thickness and height on the electric field enhancement is analyzed,and then the electric field distribution of the conical tip is analyzed.Numerical calculations are also carried out to verify the effectiveness of the designed tip structure in electric field enhancement.A new tip is prepared using the tip preparation device of laboratory,and the Raman spectrum of the single-walled carbon nanotube sample is plotted using a TERS measuring device.Finally,based on the best-enhanced stepped tip,the influence of factors such as the tip curvature radius,the laser incident angle,the type of substrate and the tip-substrate gap on the enhancement effect of the TERS system is analyzed.The results show that under the excitation of a light source with a wavelength of 632.8 nm,the Ag-coated SiO₂ stepped tip-Au/CNTs three dimensional substrate structure has the best field enhancement effect.When the tip curvature radius is 5 nm,the thickness of the Ag film is 15 nm,the height of the Ag film is 300 nm,the diameter of the Au nanoparticle is 30 nm,the laser incident angle is 45°,and the tip-substrate gap is 1 nm,the TERS enhancement factor is maximized and can reach the order of 10⁸.