Preparation Of Pyramidal SERS Substrate And Research On The Enhancement Mechanism

Raman spectroscopy is an efficient method to achieve low-concentration molecular detection.The preparation of metallic substrates with rough surface has become a general solution to enhance Raman signal.However,the commonly used preparation techniques of substrates have high costs,low sensitivity and poor stability.Based on the template stripping method,we proposed to use the crystalline silicon solar cell substrate as the template to prepare the noble metallic SERS substrate with good sensitivity and uniformity.We selected a crystalline silicon solar cell substrate with pyramidal morphology on the surface as the template,and took advantage of the weak bonding force between the noble metal and silicon to facilitate the stripping of the noble metal film from the template;UV curable polymer was selected as the polymer to assist the stripping process,its strong flexibility protected the inverted pyramidal morphology of the noble metal film from damage and formed a flexible noble metallic substrate with good Surface-Enhanced Raman Scattering（SERS）effect after stripping.Two kinds of noble metals（Au and Ag）and the positive and inverted pyramidal structures produced before and after stripping formed four kinds of pyramidal substrates,experiments proved that these four substrates can enhance the Raman spectra of R6G probe molecules,which preliminarily explained the enhancement mechanism of the positive pyramidal substrate is mainly Surface Plasmon Resonance;Ag inverted pyramidal substrate had the strongest SERS performance among four substrates,and the lowest detection concentration for R6G molecules was 10^-12 M;we also proved that the Si template or UV curable polymer under the noble metallic film would not affect the enhancement of the pyramidal SERS substrate.The Finite-Difference Time-Domain method was used to numerically analyze the electric field distribution on the surface of the substrate,we designed suitable simulation model for both positive and inverted pyramidal substrates,and explained that the enhancement mechanism of the positive pyramidal substrate is SPR effect;we demonstrated that the nano-scale pits generated on the surface of Ag inverted pyramidal substrate after stripping had greatly enhanced the electric field,which proved that the enhancement mechanism of the inverted pyramidal substrate is scattering;it was proved that the surface morphology of the substrate makes it possible to obtain electric field enhancement in the direction perpendicular to the polarization of the excitation light,so it also showed that Ag inverted pyramidal substrate had the best SERS performance among the four substrates.A comprehensive analysis of the effects of various factors on the SERS performance of the pyramidal substrate was proposed,an operation method to ensure the SERS effect of the substrate was put forward;the Raman signal can still be detected after immersing the substrate in probe molecule solution with the concentration of 10^-9 M and rinsing it with deionized water once,which proved the good adsorption of the substrate;we proved the influence of excitation light wavelength on the SERS performance of the substrate;simulation results confirmed that the random size of the pyramid array would not reduce the SERS performance of the substrate.Finally,Ag inverted pyramidal substrate with the best SERS performance was applied to low-concentration plasmid DNA detection,which realized the high-efficiency identification of 7 characteristic peaks,the RSD at the characteristic peak of 1006.9 cm^-1 of four random positions on the substrate was only 3.51%.