Surface Enhanced Raman Scattering Performance Research Of The Substrate With Three Dimensional Array Structure

Raman scattering is a special kind of scattering when transparent gas, liquid and solid medium interact with incident light, also known as the Raman effects. The essence of Raman scattering is that inelastic collision occurred between the incident light and scattering molecules lead to the changes of the scattering molecules vibration energy and rotational energy when the incident light through the medium, so the frequency of the scattered light is different from the incident light. Raman scattering frequency difference is determined by the nature of the scattering molecules, and each material has its own particular frequency difference, so the Raman scattering is often used to study the molecular structure or qualitative and quantitative analysis the scattering molecules with the characteristics of rapidly, simply, repeatedly and nondestructively. But, Raman scattering belongs to the type of inelastic scattering and the process has energy exchange, which causing its scattering intensity relative to the elastic scattering type of Rayleigh scattering is much weaker. Raman differential scattering cross section is one of the important indicators of scattering intensity, and the Raman scattering cross section (e.g. 10-25～10-30cm2sr-1) of most molecules relative to the fluorescent small ten orders of magnitude, so that the weak scattering strength cannot satisfy the actual needs. At the same time, the strength of the Raman signals is far away from the instrument response limit, if the concentration of the analyte is too low, this feature seriously hindered the Raman spectroscopy application fields. In recent years, the surface-enhanced Raman scattering (SERS) is becoming a hot topic of research, which makes the application range of the Raman Scattering expanded to many areas. The principle of SERS is the combined action of the Electromagnetic enhancement (EM) on the surface roughness of metal caused by local surface excited plasmons, and the point of Raman enhancement activity caused by the interaction of atom clusters on the rough surface and its adsorption molecules. The enhancement factor (EF) gets to103～107, which decided the high sensitivity and selectivity, and make it become the powerful tools for the qualitative detection of molecular structure.SERS is suitable for characterization of interface with high detection sensitivity, high resolution, small interference of water, good fluorescence quenching, good stability, and widely used in many fields, especially for micro trace poisonous and harmful material detection, the real-time monitoring of the chemical reaction process and current used in the field of biological detection of organism and living material. Meanwhile, the rapid development of nanotechnology makes preparation of various morphology of high stability, high performance of SERS active substrate be possible. The adsorption behavior and specific functional was studied of specific molecules that absorbed on active basal surface to be used in specific areas, eventually, have a deep understanding to SERS enhancement mechanisms by experiment and theory study, and this approach has become the SERS research direction.In this thesis, the Au nanoparticles、nanoporous gold film/Silicon nanowire array (Au NPs, NPGF/SiNWA) substrates and Ag nanoparticles/Dragonfly wings (Ag NPs/DFW) substrates were designed, which aimed at realizing detection of the trace poisonous and harmful material, biology and life material. The morphology, microstructure, performance, reusable performance, applicability and enhancement mechanism of the substrates were detailedly discussed. The main research contents of this subject are as follows.Firstly, a layer of silver nanoparticles was set on the surface of clean monocrystalline silicon slice as a seed, and then the monocrystalline slice will be made into silicon nanowire arrays by hydrothermal method with precious metals auxiliary etching, finally the size and spacing relatively homogenous Au nanoparticles were attached on the silicon nanowire arrays structure with the self-reduction properties of Au nanoparticles. Or the uniform size and spacing of Ag nanoparticles grows on the surface of the clean dragonfly wings via impregnation-chemical reduction method. Finally, characterization of the morphology structure using field emission scanning electron microscope (FESEM), high resolution transmission electron microscopy (HRTEM) and X- ray diffraction spectrometer (XRD).Secondly, Rhodamine6G (R6G) and the Crystal violet (CV) were used for measuring the enhanced capacity, stability, the quantitative relationship and reusable performance of SERS substrate systematically. The result of the test was detailed analyzed and discussed to determine the advantage and application areas of each substrate.Thirdly, the enhancement mechanism was discussed. Au NPs, NPGF/SiNWA system was simulated with the software of Finite Difference Time Domain (FDTD) based on the microstructure of substrate, and finally concluded the change rule of space distribution of electromagnetic field with the passage of time. Analysis of electromagnetic field enhancement regional type named "hot spots", and discussion was carried on the enhancement mechanism combined with the test results.Finally, the substrate of Au NPs, NPGF/SiNWA system realized to detect a wide variety of analytes and proved that it can be repeated use, which could effective implementation of the resources saving to avoid the contaminate to the environment. At the same time, Ag NPs/DFW system was used to detect micro trace amounts of toxic and harmful thiram, and comprehensive analyzed the testing results. Above all, the substrate of Au NPs, NPGF/SiNWA preliminary implementation the detection of biological molecules adenosine triphosphate (ATP), adenosine diphosphate (ADP) and single adenosine monophosphate (AMP), and the identification of organism escherichia coli (e. coli) and Staphylococcus aureus.