Preparation And Surface-enhanced Raman Scattering Properties Of Noble Metal Nanostructures

Surface-enhanced Raman scattering(SERS) has received considerable attention because of the high sensitivity, outstanding reproducibility and low LOD(limit of detection), which has been widely used in applications related to photonics, catalysis, information storage, biological medicine recent years. Due to the excellent localized surface plasmon resonance(LSPR) properties, Au and Ag nanomaterials have been widely used as SERS-active substrates. The frequencies and intensities of LSPR are affected by the compositions, shapes and sizes of noble metal nanoparticles. In this paper, noble metal nanostructures with outstanding SERS properties have been designed successfully. Factors, such as concentration of precursors, contents of seeds, reaction time and adsorbed substrates, have been studied in paper, which have great effects on the shapes, sizes and densities of noble metal nanoparticles. At last, Rhodamine 6G are used and probe molecules in the SERS experiments. The main results are as follow:At first, Au@Ag core-shell nanoparticles with various shapes and sizes have been prepared by seed-mediated growth method. The cetyltrimethylammonium bromide(CTAB) and cetyltrimethylammo- nium chloride(CTAC) are applied as surfactants, L-ascorbic acid(AA) and sodium borohydride(Na BH4) are used as reducdants, Chloroauric acid(HAu Cl4) and silver nitrate(Ag NO3) are used as precursors. The sizes and thickness of Ag shell are controlled by changing the concentrations of precursors and contents of seeds. The results show that the thickness of Ag shell could reach 8.5 nm when the concentrations of HAu Cl4 is 0.2 m M, and the contents of Ag NO3 and Au seeds are 125 μL and 300μL respectively, during which LSPR of Au@Ag core-shell nanoparticles change from two peaks(Au, Ag) to one peak(Ag). Au@Ag core-shell nanoparticles under the optimal conditions show best SERS properties, and the LOD(limit of detection) of R6 G molecules could be 10-9 M.In addition, high-yield of star-shaped gold nanoparticles have been prepared with sodium gold sulfite(Na3Au(SO3)2) solution for gold precursor by seed-mediated growth method. CTAC is used as surfactants, L-ascorbic acid(AA) and sodium borohydride(Na BH4) are applied as reducdants The sizes and morphologies of star-shaped gold nanoparticles are easily tuened by controlling the contents of precursors. Finite Difference Time Domain(FDTD) simulation was used to study the electric enhancement for the interplay between interparticles and particle-film plasmon couplings of the star-shaped gold nanoparticles. When the contents of Na3Au(SO3)2 is 150 μL and substrate is silicon wafer with 200 nm Au adhesion layer, the size and morphology distributions of samples are uniform with abundent branchs, the LSPR is wide, and the interstitial distance between nanoparticles are reduced. At last, star-shaped gold nanoparticles under the optimal conditions show best SERS properties, and the LOD(limit of detection) of R6 G molecules could be 10-14 M, showed excellent enhancements.At last, large-scale nanosheet-assembled flower-like Ag nanostructures have been successfully synthesized by a simple galvanic displacement reaction of Cu and Ag NO3 without employing any surfactants. The morphology, size, and distribution of these flower-like Ag nanostructures could be tuned easily just by controlling the reaction time and the concentration of Ag NO3, and the growth mechanisms are studied. The results show that the optimal conditions for the preparation of flower-like Ag nanostructures were achienved at reaction time of 1 min and 0.01 M concentration of Ag NO3. The size and shape distributions of nanoparticles are uniform with whole size for 10 μm, exibitied well crystallinity. Compared the SERS performances of these three nanostructures(Au@Ag core-shell nanoparticles, star-shaped gold nanoparticles and flower-like Ag nanostructures), the results indicates that star-shaped gold nanoparticles exhibits the best SERS properties, while the flower-like Ag nanostructures for worst. In addititon, SERS substrate of star-shaped gold nanoparticles posess outstanding reproducibility and stability.