【作者】 张爱平；

【导师】 方炎； 邵会波；

【作者基本信息】 首都师范大学 ， 物理化学， 2007， 硕士

【摘要】 当分子／离子吸附于金属表面后，其光物理与光化学性质常常与单纯的分子／离子或金属表面的性质不同。其中，由于分子／离子吸附于金属表面而产生的一类重要的光谱增强现象尤为突出，例如表面增强拉曼散射、反常光吸收、荧光增强或淬灭等等。本文利用化学还原法和激光烧蚀法制备出不同的纳米银胶，然后借助透射电子显微镜、拉曼光谱、紫外-可见光吸收光谱、荧光光谱等手段，研究了胶体颗粒尺寸、形貌、粒径分布和外加物质对胶体的光吸收、光致发光和表面增强拉曼光谱信号的影响。本文的主要研究内容包括：(1)借助紫外光的激发，获得了银胶较强的光致发光信号。实验显示，尺寸处于纳米级别、由许多银原子和团簇组成的银胶颗粒的光致发光能量与其表面等离子体共振吸收并非总是相同，而是受颗粒间局域场的相互作用影响极大，由此模拟出颗粒间相互作用的表面能级杂化模型。(2)利用激光烧蚀法制备了“化学纯”银胶，研究了碘酸根离子对银胶表面能级的影响及由此引起的光谱学信号的变化。实验显示，随着加入离子浓度的增加，单颗粒的等离子体共振吸收逐渐减弱，而与阴离子在银表面的化学吸附和胶体的聚沉相关的新的吸收信号逐渐增强且红移，表明离子的吸附导致了胶体表面能级的杂化，银胶体系的发光受表面能级杂化的控制。(3)实验发现，当甲基橙分子吸附于银胶表面后，其水溶液时420nm处的荧光峰被淬灭，与此同时，530nm处的荧光峰有了接近20倍的增强，同时有了约30nm的红移，本文用分子与金属表面的能量转移效应对分子荧光的影响解释了这些现象。(4)氯离子加入到甲基橙和银胶的混合体系中后，体系的光吸收、光致发光和分子的表面增强拉曼信号都发生了改变。由于氯离子的加入引起了胶体的聚沉，由此导致了分子表面吸附覆盖度的增加，并最终导致分子拉曼信号的变化，因此得出分子在银表面的单层吸附是影响拉曼信号的主要因素。同时，甲基橙分子单层和多层吸附时表面增强拉曼信号的差异表明，主导分子拉曼增强的是电荷转移增强效应，而这一增强效应在吸附疏松时较紧密时要强得多。(5)随着甲基橙-银胶体系pH值的改变，分子的拉曼信号也呈现出规律的递变。酸度值的改变造成分子结构、电荷分布的变化，根据表面增强选择定则的分析可知，分子在银颗粒表面的吸附方式也发生了改变，从而导致分子与金属表面的能量转移效率发生改变，最终导致了体系光谱学信号的规律递变。(6)借助不同的化学还原法制备了表面带不同电荷的银胶。当分子加入到表面带电情况不同的银胶后，两个体系的光吸收、荧光、表面增强拉曼信号都发生了较大的差别，且两组信号相差甚远。分析这些光谱信号发现，受库仑作用的影响，甲基橙分子通过不同的基团吸附于表面带电不同的银胶表面，由此造成分子、金属间能量转移效率的差别，因而导致了体系光谱学信号的差异。综上，本文利用不同的制备方法制备出外形、尺寸和表面带电、杂质离子含量不同的银胶，并且研究了其表面形貌、吸附离子／分子等对银胶光谱学信号的影响。随实验条件递变而规律改变的光谱学信号揭示出了分子、金属间不同的相互作用和影响这些相互作用的因素。本文实验结果将对银胶在纳米科技中的应用提供实验依据。更多还原

【Abstract】 The adsorption of molecules/anions onto metal surface leads to different photophysics and photochemistry than those found in pure molecules/anions or metal surfaces individually. One important consequence of this type of adsorption is enhancement of optical process such as surface-enhanced Raman scattering （SERS）, enhanced absorption, enhanced and quenched fluorescence and so on. Different chemical reduction methods and laser ablation method were used to prepare Ag nanoparticles, and with transmission electron microscope （TEM）, Raman detector, UV-Vis absorption and fluorescence spectrometers, we analyzed the influences of size, shape, concentration and added species to their absorptions, luminescence and SERS signals. The following topics related colloidal silver nanoparticles and their spectroscopies will be discussed.（1） Highly luminescent singles of colloidal silver nanoparticles in aqueous solution under blue excitation were detected. It was observed that Ag sol, composed of a large amount of silver atoms or particles have alterable surface energy bands different from plasmon resonance energy band of colloid due to the interactions between atoms and particles. Thus, the energy hybridization model of silver particles was deduced.（2） Laser ablated silver particles were prepared to characterize chemiadsorption of nucleophilic anion IO₃^-and its evocable spectroscopy. Besides the gradual decrease of particles’ plasmon resonance absorption with the increase of anion, some new absorption bands, assigned to different mechanisms, appeared and shifted due to chemiadsorption effect and aggregation of particles. At the same time, gradual changes and new appearance of luminescence bands indicate the hybridization of surface energy states on modified metal surfaces did happen.（3） It was found that the 420nm fluorescence band of MO aqueous solution quenched sharply. While, the enhancement factor of the other fluorescence band at 530nm was up to 20, and at the same time, the band had a red shift of about 30nm. These notable phenomena are explained in the main aspects of the influence of fluorescence quenching and fluorescence enhancing by the radiationless energy transfer channel.（4） The correspondence found between SERS, absorption and fluorescence signals points out the importance of a first layer effect to account for the changes in intensity and spectral profile observed when adding Cl^-. A different response of Ag colloids to the excitation wavelength in presence or absence of Cl^-indicates the influence of the halide on the morphology of the metal particles and, in consequence, the surface-coverage of adsorbate. The differences observed in the spectral profile of first layer SERS spectra andthe multilayer ones may be attributed to a considerable contribution of the charge-transfer （CT） mechanism to the SERS effect, which is more efficient in the first layer.（5） The gradual changes of SERS signals indicate differing adsorption orientations of dyes on silver surface when pH changed and thus, results in different energy transfer efficiencies. Both experimental evidence and theoretic analysis indicate that, different molecular structures and differing adsorption orientations of dyes on silver surface were existence when pH changed.（6） UV-Visible absorption, fluorescence and surface-enhanced Raman scattering of methyl orange adsorbed on surfaces of both positively and negatively charged colloidal silver particles were observed respectively, and compared with each other. The results indicate that dye molecules may adsorb on these two kinds of silver surface in differing adsorption orientations and interactions with different groups, and thus caused the different phenomena.In all, different kinds of silver nanoparticles were prepared and with the change of their geography （size, shape） and surface conditions （surface electricity, added species）, their spectroscopy and geography appeared disciplinarian change, which indicate different effects on optical property of colloidal Ag particles. These results may be good evidence and exploration for the application of silver nanoparticles to nanotechnology.更多还原