【作者】 刘涛；

【导师】 蒋民华； 杨德仁； 李东升；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2011， 博士

【摘要】 表面等离子共振是金属表面自由电子在光的电磁场作用下的的集体振动的现象,在传感、检测、发光、波导、太阳能光伏等多方面有重要应用前景,近年来引起了极大的关注。等离子共振的重要性质之一是使金属颗粒表面附近的局域电磁场极大增强,因而可以增强拉曼散射的强度(SERS)和提高发光体的激发强度。而金属纳米结构的尺寸、形状和结构将影响表面等离子振动的峰位和强度。因此,制备不同尺寸和结构的金属纳米结构,研究生长的动力学和热力学因素,对其实际应用具有非常重要的意义。本文用湿化学法制备了几种不同结构的金,银纳米颗粒,系统研究了控制颗粒形貌、结构的因素,探讨了颗粒的生长机理。进一步利用自组装的方法将颗粒形成薄膜,研究了颗粒薄膜的SERS’性能。并对金属颗粒的等离子振动与量子点的荧光耦合进行了初步研究。论文取得了如下有创新意义的主要结果：(1)用一步化学反应的方法,制备了不同尺寸的Ag颗粒。研究发现实验参数如AgNO3和PVP浓度、反应温度、氨水加入量等因素对产物的形貌和尺寸均有影响。并提出了颗粒生长的两种模式：扩散生长和团聚生长,小尺寸颗粒主要通过扩散生长长成,较大的颗粒则是由团聚生长得到。(2)采用油—水界面自组装的方法制备了由密排Ag颗粒形成的薄膜,研究了其SERS性能。实验发现,密排颗粒薄膜增强了R6G和pMA的拉曼信号,而且SERS效果与颗粒尺寸有关。密排颗粒膜比滴加Ag溶胶形成的稀疏薄膜具有更好的增强效果。将沉积在衬底上的密排银颗粒薄膜经过500℃热处理,制备了银岛膜；研究进一步发现,Ag岛尺寸和颗粒间距可以由薄膜层数和热处理温度来调节。(3)用改进的种子调节的化学镀方法,制备得到了具有均匀的、厚度可控的Ag层的SiO2@Ag颗粒。研究发现,加入Si02球的相对量可以来调节Ag层的厚度,而合适浓度的PVP和Ag核心的快速长大则是形成理想银层的关键。研究还指出,提高生长阶段反应物浓度,并调节温度和PVP浓度,可以提高SiO2@Ag颗粒的产量。SiO2@Ag颗粒具有从可见到近红外的可调的吸收峰,吸收峰的位置与Ag层厚度有关。SiO2@Ag核壳颗粒的SERS性能与Ag层形貌有关。(4)在无表面活性剂限制条件下,通过快速的化学反应制备了一种新型的由银核心和三维伸展的棒状凸起构成的花状Ag结构。提高反应物浓度后,得到了棒状凸起尺寸更小、更密的花状Ag结构。TEM和XRD等分析表明,花状结构的一部分棒状凸起由通常的FCC相Ag构成,而另一些棒则由HCP相的Ag构成。实验发现,HCP相的形成是在特定的还原剂甲醛的还原作用下,核心快速自由生长的结果。花状银颗粒是由HCP银的各向异性生长和甲醛氧化产物—甲酸在颗粒表面吸附导致。(5)将制备花状银结构的工艺拓展应用到表面覆盖有银核心的SiO2球上,制备得到了由SiO2@Ag核壳和Ag纳米棒组成的复合结构—海胆状SiO2@Ag结构。在海胆状结构中的Ag纳米棒中也发现了HCP相。提高反应物浓度后,海胆状结构Ag纳米棒的尺寸变小,数量更多。对比实验表明,海胆状结构形成的关键是在特定还原剂作用下,SiO2球表面Ag核心的自由和快速生长。(6)用种子法制备了不同长径比的金纳米棒,在生长阶段用维生素C作为还原剂。研究发现加入过量的维生素C时,金棒的头部会长的较大,形成肉骨头形状,同时在吸收谱中会出现第三个峰。在金棒表面包覆较薄的Si02隔离层减弱了Au棒对CdTe量子点的荧光淬灭效应。另外,由于金纳米棒的等离子共振作用,CdTe量子点的荧光寿命变短。(7)利用油—水界面自组装的方法,制备了由密排的Ag@SiO2和Au@SiO2构成的薄膜。发现由于二氧化硅的隔离作用,避免了金属核心之间的等离子振动耦合,使得薄膜具有与分散的metal@silica颗粒同样窄的消光峰。实验表明由具有较薄SiO：层的Ag@SiO2颗粒自组装得到的薄膜有效增强了R6G的拉曼信号。更多还原

【Abstract】 Surface plasmon resonance is a phenomenon that arises from the collective oscillation driven by the electromagnetic field of light. It has potential applications in sensing, fluorescence, waveguide, solar cells and so on, which have attracted a lot of attention. One of the most important properties of surface plasmon is enhancing the local filed near the surface of metallic particles greatly, which can enhance the Raman scattering intensity (SERS) and excitation intensity of fluorophore nearby. As the size, shape and structures will influence the intensity and position of surface plasmon, it is meaningful for applications to prepare metallic nanostructures of different size and shape and study the kinetic and thermodynamic factors.In this dissertation, several kinds of Au and Ag nanostructures were prepared with wet chemical methods. The factors that would influence the morphology and size were systematically investigated. The growth mechanism was also studied. And then, films composed of metallic particles were prepared through a self-assembly process, and the SERS properties were tested. Moreover, the coupling between metallic nanoparticles and quantum dots was analyzed. The primary significant results of this thesis are summarized as follows:(1) Silver particles of different size were prepared through a one-step reaction. The experimental parameters including the concentrations of PVP and AgNO3, the amount of ammonia added and reaction temperature influenced the size of the samples. Two growth modes were put forward: diffusion growth and aggregation-based growth. Small particles grew up by diffusion, while large particles grew up by aggregation.(2) Films composed of closely-packed silver particles were prepared through oil-water self-assembly. The films enhanced the Raman signals of R6G and pMA, and the enhancement effect correlated with the particle size. Films of closely-packed particles showed better enhancement than that composed of sparse particles. Ag island films were obtained by annealing the closely-packed particles and the size of the Ag islands the distance between particles were controlled by the layers of the film and the annealing temperature.(3) SiO2@Ag particles with smooth and thickness-controllable Ag shells were prepared with an improved seed-mediated electroless method. PVP of proper concentration and the rapid growth of the silver nuclei were essential to obtain perfect silver shells. The thickness of the silver shells was controlled by the amount of SiO2 spheres. By raising the concentrations of the reactants, SiCO2@Ag particles with high yield were produced. The SiO2@Ag particles displayed tunable extinction peaks spreading from the visible to near infrared region, which was dependent on the thickness of the Ag shells. The SERS effect correlated with the morphology of the Ag layers.(4) A kind of flower-like silver structures consisted of a silver core and several rod-like tips protruding in three dimensions were fabricated using a rapid reaction without the limitation of surfactants. By raising the concentrations of the reactants, more rod-like tips with smaller size on one core were obtained. TEM and XRD analysis suggested that some rods had the FCC structure, and others had the HCP structure. It was observed that the formation of the HCP phase was the result of rapid and free growth of silver nuclei under the special reducing agent-CH2O. The formation of the flower-like silver particles was induced by the anisotropic growth of HCP silver and the adsorption of HCOOH-the oxidation product of CH2O.(5) Expanding the strategies of preparing the flower-like silver particles onto the silica spheres decorated with silver nuclei, echinus-like SiO2@Ag structures, which was the hybrid structures of SiO2@Ag core-shell and silver rods were obtained. In the echinus-like SiO2@Ag structures, HCP phase of Ag was also observed. The rods on the silver shells became smaller and denser after raising the reactant concentrations. It was found that the rapid and free growth of silver nuclei on the silica spheres under the special reducing agent was also very important.(6) Gold nanorods of different aspect ratios were prepared using an seed-mediated method, in which AA was used in the growth step. Dogbone-like gold nanorods were obtained by adding superabundant AA into the growth solution. A new peak arose in the absorption spectrum of the dog-bone gold nanorods. By coating the rods with a thin silica layers, the quenching effect of gold on CdTe quantum dots was reduced. The lifetime of the excitation state of CdTe quantum dots was reduced due to the surface plasmon of gold nanorods.(7) Films of closely-packed Ag@SiO2 or Au@SiO2 particles were obtained by oil-water interfacial self-assembly. Due to the isolation of silica layers on the surface of the metallic particles, the plasmon coupling between the metallic particles was avoided. So the films displayer similar narrow extinction peaks as that of the dispersed particles in solution. Films of Ag@SiO2 particles with thin silica layers enhanced the Raman signals of R6G.更多还原