Surface Enhanced Raman Scattering Substrate With Hierarchical Structures Fabricated By Self-assembly Of Colloidal Spheres

Surface-enhanced Raman scattering as a mean of trace detection has the advantages of non-contact,low cost,high sensitivity and so on.Since the discovery of surface-enhanced Raman scattering,the exploration of SERS substrate and the mechanism of enhancement have never stopped.Sensitivity,stability,uniformity and repeatability are important indexes to evaluate the performance of the substrate.Under the premise of ensuring high performance of the substrate,it is necessary to explore a low-cost preparation method to promote the extensive application of SERS substrate.The preparation technology and mechanism of the enhancement for SERS substrate with hierarchical structure were studied here.The contents are as follows:(1)The Au Film over Nanosphere(AuFON)SERS substrate was prepared by combining spin self-assembly with ion beam sputter coating.To ensure the performance of the assembly template,concentration of monodisperse liquid was deduced from the size of spin coating substrate,materials and size match of colloidal spheres.(2)The enhancement performance of SERS substrate was controlled by the thickness of coating.Results showed that a line space of ~10nm will emerge when the PS nanospheres have a diameter of 200 nm and the coating thickness is 50 nm.Meanwhile,Metal nanoparticles with a size ~30nm covered the surface of the PS nanospheres.The Raman characterization indicated that the hotspot structures with ~10nm line gap and hierarchical structure are beneficial to the enhancement of SERS substrate.(3)The relationship between LSPR wavelength and the thickness of coating was studied here.Results showed that the enhancement performance of SERS substrate is better when the wavelength of LSPR is close to the excitation wavelength in Raman characterization process.(4)FDTD was used to analysis how the performance of SERS substrate will be influenced by multilevel structure.Meanwhile,the nano-structure spacing and relationship between the size of multilevel structure with the electromagnetic field strength were also simulated.The results show that for spherical structures with a size of 200 nm,when the spacing was about 5nm and the size of the three-dimensional gold particles was about 20 nm to 30 nm,the structure has the strongest electromagnetic field strength.