Fabrication And Characteristics Of Surface-enhanced Raman Spectroscopy Substrate Based On Template Method

Raman spectroscopy has the advantages of strong anti-interference ability,simple sampling,wide spectrum range,and relative abundance in aqueous solutions,etc.It has become a powerful tool for identifying the molecular structure of different substances.The detection sensitivity of traditional Raman scattering signal is extremely low,which limits the application of Raman spectroscopy.Surface-enhanced Raman spectroscopy（SERS）has overcome this defect and brought Raman spectroscopy back to life in its application.At present,the researh about surface-enhanced Raman scattering mainly focuses on the preparation of stable,efficient,economical and repeatable SERS substrates.The idea of SERS substrates preparation is to design templates with different dimensions as SERS substrates to provide high-density hotspot areas from multiple angles.In this paper,the electric field intensity distribution of several different micro-nano structures was simulated and analysed by the software of Finite-Difference Time-Domain（FDTD）.The SERS substrates based on black silicon were prepared by femtosecond laser irradiation of silicon wafers combined with vacuum coating technology.The main research contents are as follows:（1）Several models with different structures for SERS are designed,and the simulation analysis of the system is carried out using FDTD.For double gold nanosphere model,a better electric field enhancement effect can be obtained when it is arranged horizontally,and the particle spacing that produces the best enhancement effect is within6nm;for the double Au nanosphere and Al₂O₃/Au plane substrate model based on bulk plasmon polaritons resonance,as well as the Au/Ag nanosphere and Al₂O₃/Au plane substrate model,the hyperbolic metamaterials formed by the periodic superposition of noble metal Au and dielectric material Al₂O₃ can effectively enhance the electric field.Al₂O₃ acts as an interval layer to provide space for the surface plasma resonance coupling on the surface of the adjacent Au layer.At the same time,the coupling of two nanospheres of Au/Ag materials can also produce additional electric field enhancement effects.For Ag nanospheres and Al₂O₃/Au bowl-shaped substrate models,the 5-7 nm Al₂O₃ shell provides a suitable nanogap for local surface plasma resonance.The 35 nm Au shell provides a sufficient number of free electrons to participate in local surface plasma resonance,and the individual plasma excitation stimulated by the 2-layer Al₂O₃/Au composite structure further enhances the electric field.（2）The SERS substrates based on black silicon were prepared by femtosecond laser irradiated silicon wafer combined with vacuum evaporation:under the preparation parameters of laser power of 0.2 W,scanning speed of 1.25 mm/s,laser spot diameter of300μm,and SF₆ pressure of about 70 k Pa,the surface of silicon wafer induced a smooth convex lifting array structure.With different parameters of scanning speed,laser spot diameter,the femtosecond laser power is adjusted to 0.8 W and 0.4 W respectively.Then sharp conical array structures with serious damage and slightly sharp ones with minor damage in partial area are induced on the surface of silicon wafers,respectively.The Ag film with thickness of 100 nm on the surface of black silicon（produced at the laser power0.2 W）was prepared by resistive thermal evaporation,which can produce the best enhancement effect of SERS.The detection limit of 4-MBA molecules in this SERS substrate is 10^-11M,and the enhancement factor value is 2.59×10⁶;The intensity at the characteristic peak of 1585 cm^-1 at 15 points on the SERS substrate was randomly collected.It shows that the SERS substrate is uniform with a relative standard deviation of8.24%of Raman signal.The SERS substrate can be used to detect 10^-3M 4-MBA samples at the distance of 15 m using the time-gated standoff Raman system.