Study Of 3D Surface Plasmon Structures For SERS

As one of the most powerful analytical methods,surface enhanced Raman scattering(SERS)was able to perform unlabeled single molecule detection and provided high-resolution vibration information.Its discovery was a milestone in the history of spectroscopy and analysis technology.Over the past several decades,SERS developed a series of other spectral technologies in its research field,such as fluorescence spectrum,nonlinear optics,etc,and had a wide range of applications in different directions,including electrochemistry,biology,medicine,materials science,etc.Currently,there are two generally accepted SERS enhancement mechanisms:Electromagnetic field enhancement(EM)caused by local surface plasmon resonance(LSPR)on rough metal(Ag,Au and Cu)and chemical enhancement(CM)caused by charge transfer.The enhancement of electromagnetic field caused by LSPR is widely considered to be the most important contribution of SERS enhancement.SERS based on structure is the hot research topic recently,among which the three-dimensional(3D)surface plasmons structures have the large specific surface area,which can realize the regulation of light field and the construction of multi-dimensional"hot spots"to effectively enhance the interaction between light and matter.In this paper,the surface plasmons composite structures are designed in theory and experiment by preparing 3D substrates with a large specific surface area to increase the density and intensity of"hot spots"and to further enhance the Raman signal.The finite-difference time-domain(FDTD)method was used to design the surface plasmons complex by constantly adjusting the structural parameters to explore the tuning rules for realizing the optimization of electromagnetic field enhancement,which laid a good theoretical foundation for matching the exciton energy of two-dimensional(2D)material and realizing the strong coupling of LSPR.The 3D substrates with different morphologies were prepared by chemical etching or electrospinning to realize light field regulation and improve the utilization rate of light.Homogeneous metal nanostructures were prepared by chemical sol method,chemical reduction or magnetron sputtering method,and combined with 2D materials prepared by thermal decomposition or hydrothermal method,which laid an experimental foundation for the qualitative and quantitative detection of harmful molecules with high sensitivity.The main conclusions are as follows:(1)By in-situ spinning the solution of polyvinyl alcohol(PVA)mixed with silver colloid,ordered nanofibers of PVA wrapped silver(Ag)were obtained,and then silver nanoparticles(AgNPs)were compounded by thermal evaporation to obtain AgNPs/PVA@Ag 3D SERS substrate.The detection of crystal violet(CV)and malachite green(MG)at low concentration were realized with strong electromagnetic fields generated by the synergistic effect between horizontal and vertical silver particles.We further demonstrated its great potential for in-situ detection on the complex geometric structure.(2)We presented a 3D flexible inverted pyramids hybrids system with poly(methyl methacrylate)(PMMA)films clinging AgNPs and graphene oxide(GO).By adjusting and changing the amount of silver,the best Raman enhancement characteristics were explored,and the SERS effect with or without GO was compared,which confirmed the effect of GO in SERS enhancement.The excellent sensitivity,stability and uniformity of the substrate were demonstrated by detection of Rhodamine 6G(R6G)and CV.The robust as SERS sensor was verified experimentally and theoretically,which opened a new direction for the preparation of flexible and low-cost SERS substrate.(3)We proposed a method to construct the heterogeneous and cross-distributed Au NPs-AgNPs bi-metal structure hybridized with MoS₂on pyramid silicon(P-Si)as SERS substrate(Au NPs-AgNPs/MoS₂/P-Si)to realize the detection of R6G,CV and MG at low concentration.The electric field intensity of single metal and bi-metal were compared by FDTD solution to analyze the enhancement of surface plasmons.The P-Si was further etched to obtain MoS₂/Au NPs-AgNPs/PMMA flexible substrate to realize the low concentration detection of 10^-9M melamine,showing its great potential in the in-situ detection of toxic solution.(4)We directly grew 3D MoS₂nanocavity over P-Si microstructure to form the multiscale cavities(MSCs)composited with Au NPs to increase the propagation path of light,improve the utilization of light and further promote the interaction between photons and molecules.Theoretical simulations show that the surface of the cavity wall generates a strong electromagnetic field due to the local surface coupling effect of the Au NPs under appropriate photo-excitation conditions(?=532 nm).This structure can realize rapid detection of R6G molecules(<10^-11M),and its excellent uniformity provides a guarantee for practical application.With the support of Au NPs,the cavity structure has excellent hydrophobic effect to realize the directional detection in oil-water mixed solution,and shows its great potential in sewage detection.In addition,due to its high light utilization and rapid electron transfer rate,the substrate can realize photocatalytic degradation of dye molecules with good self-cleaning ability and recycle performance.(5)We prepared Ag-Au bimetal with different particle sizes and combined MoS₂as a supporting layer decorated on FTO conducting glass(MoS₂/Au/Ag)with size effect generating multiple surface plasmons coupling with good synergistic enhancement of SERS and PEC performance.The FDTD was used to simulate the electric field distribution of MoS₂,MoS₂/Au,MoS₂/Ag and MoS₂/Au/Ag,proving that the ternary heterostructure has the strongest electric field,which is further confirmed by the experimental results of R6G detection.The work has a wide application prospect in the realization of SERS and PEC synergistic enhancement.