Surface-enhanced Raman Scattering Study On Composite Structure Of Gold Nanocube And Gold Thin Film

The surface plasmon resonance coupling effect in metal micro-nano structure can produce high electric field enhancement,which is widely used in surface-enhanced Raman scattering（SERS）.In order to realize the SERS detection of lower concentration substances,the development and fabrication of SERS substrates with various shapes and higher electric field enhancement have been the research direction of researchers in related fields.In this paper,the composite structure of gold nanocube and gold film as SERS substrate is designed and fabricated.The surface plasmon effect exists in the composite structure is studied by finite element method,and the optimized parameters are obtained.The SERS effect of rhodamine 6G（R6G）probe on the composite substrate was studied by changing the concentration of the aqueous solution and the thickness of the PMMA spacer.The lowest detection concentration of R6G probe molecule on the composite SERS substrate can reach10^-1212 mol/L.The composite SERS substrate has the advantages of easy preparation,low cost,high sensitivity and excellent stability,which can be widely used in low concentration detection.1.A composite structure of gold nanocube and gold film is designed.From the bottom to the top,it is SiO₂ substrate,5 nm titanium film,50 nm gold film,PMMA spacer and gold nanocube.The wavelength of 633 nm is used as the excitation source.Through the study of the electric field distribution of the composite structure of gold nanocube and gold film,it is found that the composite structure has a great enhancement effect on the electric field strength.For the composite structure of different sizes of gold nanocube and gold film,there is an optimal thickness of PMMA spacer.Taking the gold nanocube with a side length of 170 nm as an example,the optimal thickness of the PMMA spacer of the composite structure is 35 nm,and the maximum electric field intensity（E/E₀）of the structure is 29.9.2.The effect of different concentration of gold nanocube aqueous solution on the composite SERS substrate was studied.The mixed solution of 90 nm gold nanocube and R6G with different concentrations was dropped on the PMMA-gold film substrate prepared by magnetron sputtering,and the SERS substrate of the composite of gold nanocube and gold film was obtained.In the mixed solution of 10^-44 mol/L R6G and5.625μg/mL 90 nm gold nanocube,the SERS signal of the composite SERS substrate is the largest,which is 9 times stronger than that of single gold nanocube.3.170 nm gold nanocubes and gold thin film composite SERS substrates with PMMA spacings of 0,14,25,30,36,50,and 70 nm were prepared experimentally.The SERS effect of the R6G molecule was studied,and the results show that when the thickness of the PMMA spacer layer is 35 nm,the SERS signal of the composite SERS substrate is the largest,which is five times than that of a single 170 nm gold nanocube structure.It is three times the intensity of the Raman signal of a composite SERS substrate with a PMMA spacer layer thickness of 0 nm.4.The minimum detection concentration of R6G in the composite SERS substrate was studied.The minimum detection concentration of R6G with a composite structure of 90 nm gold nanocube and gold thin film is 10^-1111 mol/L.And The minimum detection concentration of R6G with a composite structure of 170 nm gold nanocube and gold thin film is 10^-1212 mol/L.The composite SERS substrate with a 30 nm thickness PMMA spacer under the condition of the mixed solution of 10^-44 mol/L R6G and 5.625μg/mL 170 nm gold nanocub was used to study the SERS spectrum of the sample after 112 days of exposure.The results show that the intensity of the second Raman signal is 90%to that of the first time,which shows that the composite SERS substrate has good stability.