The Fabrication Of Periodical Ag/polymer Nanostructure And Its SERS Performence

Environmental pollution has become one of the major obstacles to economic development in today’s society. How to detect toxic chemical and biomolecular in water and food in a fast and convenient way has been intrigued the researchers around world. Surface-enhanced Raman scattering (SERS) has gained a reputation as one of the most sensitive spectroscopic methods for chemical and biomolecular sensing since its discovery, especially in detection. Earlier researches have been focused on the fabrication of novel nanoparticles which is usually dispersed in solution. Although, this type of SERS substrate has achieved great SERS activity, the irreproducible SERS signals has restrained its application in reality. Currently, many researchers have tried to fabricate the periodic noble metal nanostructures to improve the reproducibility of SERS signals. Nanoimprint lithography (NIL) is proven to effectively fabricate large scale of nanostructure templates with simple process, high throughput, reusable and relatively low cost characteristics. Thus, this work is aimed at the fabrication of high quality SERS substrate by the combination of NIL and deposition methods.The processes of fabrication of polymer nanorode arrays with silicon nanohole array and anodized aluminum templates are described in detail. By adjusting the embossing temperature and pressure parameters, the optimum morphology of polymer nanorod array were obtained at155℃and20bar.We used mirror reaction to decorate the polymer nanorod with80nm Ag nanoparticles to form non-regular-spherical Ag/polymer nanorod array (NRSAPNA). The effects of reaction time and solution concentration on the coverage of Ag nanoparticles were investigated. It must be mentioned that, prior to the growth of Ag NPs, the patterned polymer film substrate need to be treated with oxygen-plasma to improve the surface hydrophylicity of polymer film. It was found that the hydrophilic treatment is not only beneficial to the dispersion of silver nanoparticles over the polymer surface, but also provide a large number of stronger anchoring sites for the silver nanoparticles deposition onto the polymer surface. The as-synthesized NRSAPNA exhibited a remarkable SERS activity, the detection limit for R6G is10"12M and the enhancement factor EF is5.1×107. SERS signal stability of NRSAPNA was also studied, the relative standard deviation (RSD) of SERS signal is less than15%. In addition, the effects of Ag nanoparticle morphology on SERS performance have been discussed. It proved that NRSAPNA with a high specific surface area and rough surface could show a strong SERS activity.The UV-induced reduction is usually used to prepare silver nanoparticles in the liquid phase. In this thesis,25nm-silver nanoparticle was deposited onto the surface of the solid polymer nanorod by the combination of photochemical reduction and nanoimprint technology, forming a regular-spherical-Ag/polymer nanorod array (RSAPNA). Comparative studies of UV-visible absorption spectrum showed that the sodium citrate play a key role in the reaction. The as-synthesized RSAPNA exhibited a relatively high SERS activity and Raman signal reproducibility to R6G, the detection limit is10-11M.Vertically aligned Ag nanosheet clusters (ANC) array can be achieved by the combination of UV-NIL and electrochemical deposition method. To obtaining reproducible ANCs array, we have systematically investigated the factors that influenced the electrodeposition. It was found that the formation of uniform ANC s is strongly depended on the seeding layer, citric acid concentration, appropriate electrodeposition potential and time. We proposed the growth mechanisms of Ag nanosheet assembled were oriented attachment growth and Oswald ripening. The detection limit of the as-synthesized ANC A is10’13M and the enhancement factor EF is3.3×108. The comparison of SERS performance between ANCA and Ag nanosheets film verifies that the SERS reproducibility was greatly improved,the RSD value of ANCA is half of those of Ag nanosheets film.