Surface-enhanced Raman Scattering Study On The Composite Structure Of Gold Nanodisk Array And Gold Thin Film

Since it was discovered by Fleischmann in 1974,surface-enhanced Raman scattering(SERS)has received extensive attention from researchers.The reason is that SERS can analyze and identify molecular structures at low concentrations,and the detection limit reaches the molecular level.In recent years,the research of SERS has mainly focused on searching for high-efficiency SERS substrates with good uniformity,high stability,and strong practicability.Due to the excellent surface plasmon properties of noble metal nanostructures,it is considere d to be an efficient SERS substrate.Therefore,how to optimize the noble metal nanostructures and fabricate efficient SERS substrates is a problem that researchers have been solving.In this paper,a composite structure of Au nanodisk array and gold film is designed and fabricated,which is used as a SERS substrate.This structure can excite localized surface plasmons and propagative surface plasmons,so that the two have a strong resonance coupling.The surface plasmon effect of the structure was studied by the finite difference time domain(FDTD)method.Furthermore,we experimentally fabricated the designed SERS substrate sample,used R6G as the Raman probe molecule,tested the Raman spectrum of the composite SERS substrate,studied the stability of the SERS substrate,and calculated its Raman enhancement factor(EF).The results show that the designed SERS substrate can perform Raman detection at a single wavelength and dual-wavelength,and has good SERS characteristics.In this paper,the structure morphology,SERS performance,and enhancement mechanism of the composite substrate are characterized,tested,and discussed in detail.The specific content is as follows:1.A composite structure of Au nanodisk array and gold film for single wavelength excitation of SERS is designed.The structure from top to bottom is 50-nm Au nanodisc array,5-nm Ti nanodisk array,25-nm Si O2 film,100-nm gold film,10-nm Ti film,and 1-mm quartz substrate.The nanodisk array has a period of 750 nm and a radius of 125 nm.When the incident light wavelength changes from 500 nm to2000 nm,the reflection spectrum of the composite stru cture has three resonance modes.By optimizing the parameters of the structure,the resonance wavelength of mode 2 is adjusted to 785 nm for SERS experiments.2.A composite structure of Au nanodisk array and gold film that can be used for dual-wavelength excited SERS is optimized and designed.The structure is still Au nanodisk array,Ti nanodisk array,Si O₂ film,gold film,Ti film,and quartz substrate,from top to bottom,the thickness is 80 nm,5 nm,40 nm,100 nm,10 nm,and 1 mm in order.The radius of the nanodisk is 70 nm,and the period of the array is 580 nm.When the incident light wavelength changes from 500 nm to 2000 nm,the resonance wavelength positions of the reflection spectrum are located at 633 nm and 785 nm,respectively.3.In the experiment,a single-wavelength excited SERS composite substrate was fabricated by photolithography and electron beam evaporation.The thickness of the structure from top to bottom was 50 nm,5 nm,25 nm,100 nm,10 nm,and 1 mm.The morphology of the structure was characterized by scanning electron microscope(SEM),and the period of the nanodisk array was 759 nm and the diameter was 256 nm,and the error with the design parameters was less than 1.5%.Rhodamine 6G(R6G)was used as the Raman probe molecule to study the Raman spectrum and stability o f the composite SERS substrate.The Raman intensity of the substrate decreased by 17.1%after 30-days.4.The composite substrate with dual-wavelength excited SERS was fabricated experimentally,and the thickness of the structure from top to bottom was 80 nm,5 nm,40 nm,100 nm,10 nm,and 1 mm,respectively.The fabricated nanodisk array has a period of 580 nm and a diameter of 145 nm,and the error with the design parameters is less than 3.5%.The Raman spectrum of the composite SERS substrate was studied experimentally,and its Raman enhancement factor was 2.9×10⁴.Theoretical and experimental results show that the substrate successfully realizes material detection at two wavelengths,and has good SERS characteristics at both wavelengths.