| Anisotropic plasmonic nanoparticles have unique optical and electronic properties,so anisotropic nanoparticles are increasingly used for self-assembly into ordered array structures.The easily tunable optical properties of anisotropic gold nanorods make them the most useful self-assembled gold nanoparticles.The gold nanorod array structure formed by self-assembly has excellent optical properties,which can be easily adjusted by adjusting the aspect ratio and spacing of the gold nanorods.However,compared with the extensive study of the effect of aspect ratio on the optical properties of single gold nanorods,so far the influence of gold nanorod diameter(absorption scattering ratio)on the plasmon enhancement ability of self-assembled array structures has not been reported,and there is no in-depth study on the specific mechanism of plasmon resonance enhancement of gold nanorod array structures with different diameters.In this thesis,the above problems are tried to be explored through a combination of experiments and theoretical simulations,and the main results obtained are as follows:1.The evaporation-induced self-assembly standing arrays of gold nanorods of different sizes are realized on silicon and glass substrates.The method used is simple and reliable,meanwhile,requires lower experimental conditions.Gold nanorods with a diameter of 22 nm,length of 51 nm,and diameter of 41 nm,length of 96 nm are selected.The aspect ratios of the two gold nanorods are close,so the wavelengths of longitudinal surface plasmon resonance peaks are also similar.The experiments specifically analyzed the three forces between adjacent gold nanorods during the formation of selfassembled structures: electrostatic force,van der Waals force,and dissipative force,among which electrostatic force is repulsion,van der Waals force and dissipative force belong to attraction.When the combined force of these three forces is zero,the gold nanorods can self-assemble into a stable array structure.When calculating the resultant force,it is found that the dissipative force is negligible relative to the other two forces,so the van der Waals force and the electrostatic force play a decisive role in the selfassembly process.The theoretical analysis found that the van der Waals force and electrostatic force are determined by the surface Zeta potential of gold nanorods and the Debye length of gold nanorods in solution,and these two key parameters can be controlled by adjusting the concentration of gold rods and hexadecyl trimethyl ammonium bromide(CTAB)in the solution.Finally,the self-assembly conditions of gold nanorods with a diameter of 22 nm were determined experimentally by the control variates: CTAB concentration of 3.6 m M,gold nanorod concentration of 7.6 n M;selfassembly conditions of gold nanorods with a diameter of 41 nm: CTAB concentration3.6 m M,gold nanorods concentration 29.7 n M.After testing,the gold nanorod array structures formed by this experimental method is relatively stable,and there will be no damage after spin-coating ethanol or stored for 3 months.2.Unlike the longitudinal surface plasmon wavelength of Au nanorods and the spacing between adjacent Au nanorods in Au nanorod arrays,the role of Au nanorod diameter in the plasmon enhancement capability of vertical Au nanorod arrays is rarely explored.In this experiment,two gold nanorods with similar longitudinal surface plasmon resonance peaks but different diameters are selected,and their optical properties were determined by the absorption and scattering cross sections,respectively.The conversion efficiency of nonlinear nanocrystals is usually low,and it can be greatly improved by coupling with plasmonic metal nanostructures.Therefore,the vertically aligned gold nanorod arrays formed by evaporation-induced self-assembly are coupled with the spin-coated nonlinear Zn O nanocrystal film on their surface.The results show that vertical Au nanorod arrays with a larger diameter(41 nm)can enhance the second harmonic generation(SHG)of Zn O nanofilm by 27.0 times,compared with about 7.3times for the smaller vertical Au nanorod array(22 nm).Theoretical simulations indicate that such stronger enhancement of the larger vertical gold nanorod array compared with the smaller one is due to its stronger scattering ability and greater extent of near-field enhancement at SHG fundamental wavelength.Our work shows that the diameter of gold nanorods is also an important factor to be considered in realizing strong plasmon enhancement of vertically aligned gold nanorod arrays.3.Fluorescence detection technology has the incomparable advantages of high sensitivity and in vivo detections,but conventional fluorescent molecules are limited by low efficiency.The surface plasmon resonance can achieve a large multiple of fluorescence enhancement,so the study of the surface-enhanced fluorescence spectrum of metal nanostructures is particularly important for the development of fluorescence detection technology.A composite structure of gold nanorods standing array with Cy3-doped poly(methyl methacrylate)(PMMA)film was constructed,and the maximum enhancement effect was achieved by adjusting the thickness of the PMMA film from 6nm to 39 nm.The experimental results show that the gold nanorod arrays with the diameters of 41 nm and 22 nm can achieve a maximum enhancement of 102 and 38 times on the fluorescence of Cy3 molecules when the thickness of PMMA is 15 nm.By the dark field spectra of the gold nanorod array structures and the change of the fluorescence decay rate of fluorescent molecules,the mechanism on the plasmonenhanced fluorescence intensity was explored,and it was found that the fluorescence enhancement effect came from three aspects: excitation enhancement,emission enhancement,and collection efficiency enhancement.Finally,the far-field and nearfield electromagnetic field distributions of gold nanorod array structures with diameters of 41 nm and 22 nm were simulated by the finite difference time domain method(FDTD),which verified the above experimental results further. |
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