Preparation And Surface Enhanced Raman Spectra Research Of Silver/Silicon Nano-Heterostructures

As the Raman spectra directly reflect the internal structure ofmolecular and given the molecular "fingerprint spectra", it is oftenused for the analysis of organic molecules. However, due to theRaman scattering cross section more than ten orders of magnitudelower than the fluorescence scattering cross section, the Ramanscattering signal intensity is very weak. If molecular concentrationis slightly lower, the detection sensitivity of Raman spectra will notbe able to meet the requirements. So the application of conventionalRaman spectra is greatly limited. In recent years, by using thecollective oscillations of free electrons in the metal as known assurface plasmon resonance, surface enhanced Raman spectra (SERS)technology greatly enhancing the Raman signal intensity. And therange of Raman spectroscopy applications is rapidly expanding.Base on the tantalizing prospect of SERS spectra in the tracespecies detection, new structure substrates, high-performance SERS active substrates, molecular adsorption rules of the substrate surface,SERS mechanisms and to promote the application of SERStechnology has become a hot topic of today’s research. This thesisfocuses on the preparation of the SERS substrate, proposed a novelSERS substrate with high enhanced performance and high stability,the main contents are as follows:First, a regular three-dimensional micro-nano structuresubstrate based on Ag/Si heterojunction array with highly SERSsensitivity was fabricated. The porous silicon nanowire arrays(PSNWA) with a high specific surface area were prepared frommonocrystalline silicon by metal-assisted etching method. Then Agnanoparticles (Ag NPs) were prepared by direct reduction in thesurface of PSNWA, and Ag/PSNWA hybrid nanostructures werefabricated. Use XRD, SEM, TEM, HRTEM and EDS for itsstructure, morphology and composition characterization.Second, SERS substrate has achieved high stability, highenhancement and quantitative detection of probe molecule. We useRhodamine6G (R6G) as probe molecules to characterize the SERSperformance of Ag/PSNWA substrate including enhancedperformance, quantitative relations, homogeneity, reproductionperformance and time stability. We use Ag/PSNWA substrate todetect thiram which is a commonly used pesticide in agriculture. Quantitative Relationship between thiram concentration and Ramanintensity was obtained.Third, SERS enhancement principle of Ag/PSNWA substratewas deduced. We use finite difference time domain (FDTD) methodto simulate the surface electric field distribution of Ag/PSNWAsubstrate which is in the external laser irradiation. Analysis eachpart of the Ag/PSNWA nanostructure’s contribution in SERS.