| Surface-enhanced Raman scattering(SERS)mainly uses the electric field enhancement effect caused by plasmon excitation with metal nanostructure to amplify the Raman signal,thus obtaining the structural information of adsorbed molecules.Currently,it has developed into a powerful and non-destructive analysis method,which is widely used in analytical science,biomedicine,environmental monitoring and other fields.The properties of surface enhanced Raman substrates are mainly determined by the structural characteristics of metal nanostructures.Studies have shown that due to plasmon excitation and coupling,the significantly enhanced local electromagnetic fields("hot spots")are generated near the tip of metal nanostructures and in the gaps between adjacent metal nanostructures.It is the key to obtain high-intensity and high-density electromagnetic "hot spots" for the realization of highly sensitive SERS detection.The larger surface area of the three-dimensional array structure can adsorb more molecules to be measured,which provides the possibility for the generation of high-density "hot spots".In addition,the natural anti-reflection structure of the three-dimensional array can capture more incident photons and excite Raman scattering,which is also conducive to improving the sensitivity of Raman detection.Based on the above background,this study combines V Shape anodic aluminum oxide(AAO)template and physical vapor deposition technology,large-area ordered silver nano-cone arrays were prepared.On this basis,high-density gold nanoparticles were loaded on silver nano-cones by thermal evaporation,and a three-dimensional hybrid system with multiple plasmon coupling was constructed.The electric field enhancement effect in the system was studied,and highly sensitive SERS detection was realized.The specific research results are as follows:1.A new method for preparing ordered metallic nano cone arrays was developed.Through adopting V-shaped alumina templates with different structures,three kinds of silver nano cone arrays with different aspect ratios were prepared to study their electric field enhancement and Raman enhancement properties,combined with FDTD simulation and Raman measurement.The results show that the surface of the silver nano cone array exhibits multiple plasmon resonance under the excitation of light.Compared with single silver nano cones,the plasmons coupling between adjacent silver nano cones in the array occurs,and the electric field near the surface of the nano cone increases significantly,and the electric field enhancement effect increases with the increase of aspect ratio of silver nano cones.Raman test showed that the silver nano cone array had good SERS sensitivity,the enhancement factor for CV and R6G molecule was up to 106 magnitude,the detection limit was 10-8magnitude,and the signal homogeneity was good,the relative standard deviation of the signal was 6.7%.2.Thermal evaporation was used to load high-density gold nanoparticles on the surface of ordered silver nanocone array to construct a three-dimensional hybrid plasmon system.Combined with Raman measurement and FDTD simulation,the results show that this silver nano cone loaded with gold nanoparticle generates strong inter-particle strong coupling,particle-membrane coupling and particle-cone coupling,producing significantly enhanced electric fields on the nano cone surface.The multiple plasmon coupling generates high-density electromagnetic hot spots,resulting in highly sensitive detection of CV and R6G molecules with an enhancement factor of about 1.74×108,a detection limit of 10-10 M and a relative standard deviation of less than 13%.In addition,there is a linear correlation between Raman intensity and logarithm of concentration,conferring quantitative analysis capability to this nano cone array.3.Four substrates with different dielectric properties,including aluminum,silicon,sapphire and quartz,were selected,and disordered and ordered two-dimensional silver nanoparticle arrays were prepared by thermal annealing and template-assisted methods respectively.By adjusting silver deposition thickness,annealing temperature and template structure,the size and distribution of silver nanoparticles were adjusted.On this basis,the influence of dielectric properties of this four substrates on SERS enhancement was studied.Results of Raman test show that the silver nanoparticle array on the surface of aluminum substrate has the strongest SERS signal,followed by the silicon surface and the weakest on quartz surface.Therefore,dielectric property of substrate has a certain influence on SERS enhancement,which is of great significance for understanding the plasmon characteristics of metal nanostructures and further optimizing the properties of SERS substrates. |
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