Research On Fabrication And Performance Of Multi-dimensional SERS Substrates Based On Ordered Silicon Pyramids Array

Surface enhanced Raman Scattering（SERS）is a high-sensitivity detection technique for low-concentration analysis.By measuring the intensity and location of fingerprint peaks,quantitative and qualitative analysis of trace substances can be achieved.In order to improve the comprehensive performance of SERS sensing,the researchers improved SERS substrates by adjusting the morphology,constructing ordered arrays,and compounding various materials.But for now,there is a problem that the construction method of SERS ordered array is not universally applicable.At the same time,the Raman enhanced mechanism of composite SERS substrates still needs to be explored.Especially for the SERS substrates fabricated by noble metal and semiconductor,it is unclear whether the built-in electric field generated by the substrates contributes to enhanced Raman signals.In order to solve the above problems,this paper designs a universal scheme based on colloidal spheres mask wet etching and interface assembly technique,and fabricated ordered silicon pyramids array substrates.Subsequently,nanobowls,nanorods,nanotubes and core-shell nanorods array were constructed on the surface of the ordered silicon pyramids array,and the multi-dimensional SERS substrates were obtained after composite with noble metals.All these SERS substrates have excellent sensitivity and uniformity,and these can achieve quantitative and qualitative analysis of trace substances.At the same time,the effect of anti-reflection on Raman enhancement was explored,and the mechanism of the built-in electric field generated by charge separation on Raman enhancement was also studied.These are as follows:First,we through the unconventional colloidal spheres mask method and wet etching method to fabricate an ordered silicon pyramids array（Si-p）.And then we assemble continuous Ag nanobowls（Ag-NBs）on the surface of Si-p,to form a bionic compound eyes SERS substrate（Ag-NBs/Si-p）with anti-reflection properties.The Raman signal generate by the bionic Ag-NBs/Si-p substrate is significantly higher than the non-bionic Ag-NBs substrate,which fully reflects the advantages of the anti-reflection structure in Raman enhancement.Furthermore,the bionic anti-reflection theoretical model is established by the finite difference time domain（FDTD）method to elucidate the physical field enhancement mechanism of the anti-reflection structure.Second,using the ordered silicon pyramids array as the substrate,ZnO nanorods are assembled on the surface of Si-p through the heterogeneous interface seed induction method.And then Ag nanoparticles（Ag-NPs）are grown on the surface of the nanorods by ultraviolet in-situ reduction method.The bionic“flower-like”ZnO nanorods composite SERS substrate（Ag/ZnO/Si-p）modified by Ag-NPs is formed.Analyze the Raman signal enhancement mechanism of Ag/ZnO/Si-p by integrating sphere absorption spectrum,X-ray photoelectron spectroscopy,surface photovoltage spectrum,and surface photovoltaic phase spectrum.Furthermore,the effects of the anti-reflection property of the bionic structure and the charge separation of the hetero-interface on the intensity of the Raman signal are summarized.Third,ZnO nanorods are used as sacrificial templates to assemble zinc ferrite（ZnFe₂O₄）nanotubes on the surface of Si-p.And then Ag-NPs are grown on the surface of the inner and outer walls of ZnFe₂O₄ nanotubes by ultraviolet in-situ reduction method.The bionic"flower-like"ZnFe₂O₄ nanotube composite SERS substrate（Ag/ZnFe₂O₄/Si-p）modified by Ag-NPs is formed.Furthermore,we clarify the Raman enhancement mechanism of anti-reflection and charge separation.At the same time,Ag/ZnFe₂O₄/Si-p exhibits excellent performances such as low detection limit,strong recognition ability,good reproducibility,and reusability in Raman sensing detection of trace harmful dyes.Fourth,the metal-organic framework materials（ZIF-8）in situ grows on the outer surface Ag/ZnO/Si-p the composite SERS substrate,by using hydrothermal assembly technology to form ZIF-8/Ag/ZnO/Si-p SERS substrate.By using the adsorption advantage of porous ZIF-8,the sensitivity of SERS substrate to detect 4-mercaptopyridine is improved.Meanwhile,because of the ZIF-8 surface has negatively charged,it has a repulsive effect on chloride ions.ZIF-8 can reduce the corrosion of chloride ions to Ag-NPs,and enhancing the service life of the SERS substrate.