Construction Of Three-dimensional SERS Substrate By Reactive Ion Etching And Performance Stud

Surface Enhanced Raman Scattering（SERS）,also known as SERS,refers to the adsorption of some molecules on rough metal surfaces,such as gold,silver or copper,and these Raman signals are significantly enhanced.As a spectral technology,SERS has been widely used in many fields,such as chemistry,biology,medicine,nano-materials,environment,food and so on.Preparing high-performance substrates is the key to the wide application of SERS technology.However,it is still challenging to manufacture SERS substrates with high performance,repeatability and high cleanliness by simple and easy-to-operate methods.In this paper,in order to prepare a high-performance SERS substrate,reactive ion etching（RIE）technology was used to etch silicon wafers and polystyrene（PS）microspheres.By changing the etching conditions,a high-performance three-dimensional SERS substrate was prepared,which can be used to detect trace harmful molecules.Finally,the etching mechanism was explained.The main research contents of this paper are summarized as follows:（1）A new simple method is proposed to fabricate large-size vertical hollow circular cylind ordered array（HCCA）.A single layer of PS microspheres was laid on the silicon wafer by gas/liquid interface self-assembly,and etched by RIE technology.HCCA was prepared for the first time by adjusting parameters.It is proved that the surface of silicon nano-column is wrapped with a special material,which is Al F₃,by scanning electron microscope（SEM）,transmission electron microscope（TEM）,x-ray photoelectron spectroscopy（XPS）and other characterization methods.The preparation conditions of HCCA are as follows:SF₆and O₂are introduced,Al sample stage exists,appropriate RF power and appropriate etching time are set,etc.The gold film was plated on HCCA substrate by sputtering deposition,and it was used as SERS substrate to detect 4-ATP molecules.The experimental results show that the minimum detection limit（LOD）of 4-ATP can reach 10^-12M and the enhancement factor（EF）is7×10⁵.The finite difference time domain（FDTD）simulation explains the reason why the above-mentioned substrates have super high sensitivity in detection based on surface enhanced Raman scattering effect.（2）The effects of different etching gases on the etching of PS microspheres and silicon wafer are studied systematically,and the corresponding etching mechanism is proposed.Three kinds of etching gases,SF₆,CHF₃and C₄F₈,are introduced respectively.And the effects of gases on etching are studied by SEM,XPS and other characterization methods.The etching of fluorocarbon gas is related to the C/F ratio of the gas itself.When the ratio of F is higher,that is,the C/F ratio decreases,the etching is faster;When the ratio of F is lower,that is,the C/F ratio increases,the etching is slower,even etching does not occur,which shows that a polymer film is deposited on the surface of the etched material.When CHF₃and C₄F₈gases are used,the etching is slow,which shows that a polymer film containing fluorocarbon is formed on the surface of PS microspheres and silicon wafer.Introducing oxygen will consume C,which will reduce the C/F ratio and accelerate the etching rate.The etching mechanism of SF₆gas is different from the above,because it does not contain C and the specific gravity of F is very high,so the etching rate is very fast.The surface of the substrate etched by fluorocarbon gas is rough,and the contact angle of water droplets on its surface is about 130°,which can be used as hydrophobic or even superhydrophobic materials.The metal film is sputtered and deposited on the surface of the three-dimensional substrate etched by three gases,which is used as SERS substrate to detect molecules such as 4-ATP and R6G.Experiments show that the signal can still be detected at a low concentration of 10^-9M,and the signal uniformity is very high.