Sers Study Of Ag(Au) Nanoparticles On Three Dimensional Array Structure

Surface-enhanced Raman scattering (SERS), with ultrahigh sensitivity, allow apacetrace detection, and has been an important tool in surface science. Substrate is a key factordetermining the enhanced performance. But today the SERS substrate cannot balance wellthe simple preparation technique, the low cost and the high enhancement. Aiming to solvethis problem, in this thesis, we investigate the performance of Ag (Au) SERS substratewith three dimensional array structure. Through theoretical analysis, the relationshipbetween localized electric enhancement and the size of Ag (Au) nanoparticles is obtained.And then the best parameters are determined. Combining with the analysis results, wefurther prepared nanostructuraled SERS substrate with high density “hot-spot” inexperiments. The main research contents are listed as follows:First of all, the numerical analysis of electric field distribution of differentmorphology of Ag nanoparticles system with sphere, rice and wire shape is conducted bythe three dimensional finite difference time domain (3D-FDTD) method. Afterwards, thespherality is selected due to the enhanced effect of spherical particle is best in all, and theaffection of the Ag (Au) spherical dimer and distance on the localized electricenhancement is analyzed systematically. Meanwhile the influence of diameter, shellthickness and gap of Ag@SiO2(Au@SiO2) on the field is also illustrated. The relationshipbetween localized electric enhancement and metal nanoparticles size is obtained.And we find that an extremely high field enhancement occurs at the distance of1.2nm, i.e.SERS “hot spots”, meanwhile, the metal particles with the characters of uniformity, density and more gaps can provide more SERS “hot spots” to improve the effect of SERS enhancement effect.Secondly, combined with high density “hot-spot” model, a large-scale andthree-dimensional nanostructured Au/SiNWA as SERS substrate is prepared by thetwo-step method. The process is that Si nanowire array (SiNWA) is fabricated with simplemetal-assisted chemical etching and deposited by Au nanoparticles using metal reductionprocesses. The three-dimensional nanostructured Au/SiNWA is evaluated as an active substrate for SERS. After characterization test, the results show that the substrate haswell-pleasing stability and sensitivity. The three-dimensional layered distribution of Aunanoparticles yields more “hot-spot”, which is in agreement with the theoretical prediction.This SERS substrate has extremely high SERS activity with a calculated enhancementfactor (EF) of up to3.26×105and detection limits of10-7M for R6G. The EF is about tentimes higher than the values reported elsewhere.Thirdly, the experimental method was improved using the mastoid shapemicrostructure of dragonfly wing (DW) to replace SiNWA. A hydrophobic Ag/DW SERSactive substrate with array structure is prepared by impregnation reduction methods.Based on the basal morphology characterization, Ag nanoparticles are distributed evenlyon the mastoid shape microstructure of DW and more “hot-spot” are offered. Aftercharacterization test and performance analysis, the results show that the SERS substrate ofAg/DW has not only high stability, but also the extraordinary enhanced effect. The EF ofAg/DW SERS substrate is up to7.7×106, which is about twenty four times higher thanthat of Au/SiNWA. The detection limit of R6G is effectively downgraded to10-8Mbecause of the super-hydrophobic of dragonfly wing and is lower than that of Au/SiNWAone order of magnitude.Finally, the enhancement ability of Au/SiNWA and Ag/DW substrate is analyzed bythe3D-FDTD method respectively. Specially, the relationship between localized electricenhancement and the diameter of Ag nanoparticles gives well explanation on the affectionof repetitions to SERS signal on Ag/DW substrate. Summing up the research，Comparedwith the Au/SiNWA substrate, Ag/DW substrate not only solves the problem of the unevendistribution of metal particles, but also balances well the simple preparation technique, thelow cost and the high enhancement.