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Modeling the optical properties of noble metal nanoparticles, nanoparticle arrays, and molecule-nanoparticle complexes.

机译：模拟贵金属纳米粒子，纳米粒子阵列和分子-纳米粒子复合物的光学性质。

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The optical properties of noble metal nanoparticles have been widely used in the design of chemical and biological sensors. The efficiency of this design relies heavily on understanding the interaction of light with nanoparticles, the interparticle coupling of nanoparticles in arrays, and the interaction of nanoparticles with adsorbed molecules. In this thesis, I present theoretical modeling of these interactions and of the optical properties that result from them.;The extinction spectra of individual silver spheres of different sizes have been studied by both exact Mie theory and a quasi-static treatment. The goal here is to emphasize the usefulness of simple analytical theories for simple shapes (spheres and spheroids) in providing qualitative insight about the effect of particle size. The extinction spectra of one-dimensional linear chains and two-dimensional arrays of silver spheres have been studied using both T-matrix and coupled dipole (CD) methods. The main focus here is to determine the influence of interparticle spacings and array structures on extinction spectra, but the effect of particle size is also considered. The CD approach is shown to capture most of the array effects for spherical particles of 30 nm radius or smaller, and a semi-analytical model is proposed to interpret the simulated results using simple concepts. Both the CD and the semi-analytical approaches have then been applied to model arrays of spheroids, and the simulated spectral variations are in good qualitative agreement with experimental data on arrays of cylinders.;The correlation between enhanced Raman scattering and molecule-nanoparticle interactions has been studied using a recently developed time-dependent density functional theory method, based on a short-time approximation. The method is tested first to simulate both normal and resonance Raman scattering spectra of the uracil molecule, and then employed to study the enhanced Raman scattering of the pyridine-Ag20 complex, the pyrazine-Ag20 complex, and the Ag20-pyrazine-Ag20 junction structures. Enhancements of 105--106 are found for all three model systems, which are comparable to findings on nanoparticles. However, the relative importance of different enhancement mechanisms is found to be different for each system. Moreover, a combination of information about the vibrational motion and the local chemical environment provides a simple picture of why certain vibrational modes are enhanced more than others.
机译：贵金属纳米粒子的光学性质已广泛用于化学和生物传感器的设计中。该设计的效率在很大程度上取决于对光与纳米粒子的相互作用，纳米粒子在阵列中的粒子间耦合以及纳米粒子与吸附分子的相互作用的理解。在本文中，我给出了这些相互作用以及由此产生的光学性质的理论模型。通过精确的米氏理论和准静态方法研究了不同尺寸的单个银球的消光光谱。这里的目的是强调简单分析理论对简单形状（球体和椭球体）的作用，以提供有关粒度影响的定性见解。使用T矩阵和偶极耦合（CD）方法研究了银球的一维线性链和二维阵列的消光光谱。这里的主要重点是确定粒子间间距和阵列结构对消光光谱的影响，但也要考虑粒径的影响。展示了CD方法可捕获半径为30 nm或更小的球形颗粒的大多数阵列效应，并提出了一个半分析模型来使用简单的概念来解释模拟结果。然后将CD和半解析方法都应用到椭球的模型阵列中，并且模拟的光谱变化与圆柱体阵列上的实验数据具有良好的定性一致性;;增强的拉曼散射与分子-纳米粒子相互作用之间的相关性已经得到使用最近开发的基于时间的密度泛函理论方法，在短时近似的基础上研究了这种方法。首先测试该方法以模拟尿嘧啶分子的正常和共振拉曼散射光谱，然后用于研究吡啶-Ag20复合物，吡嗪-Ag20复合物和Ag20-吡嗪-Ag20连接结构的增强拉曼散射。对所有三个模型系统都发现105--106的增强，这与纳米颗粒的发现相当。但是，发现每个系统的不同增强机制的相对重要性不同。此外，有关振动运动和局部化学环境的信息的组合提供了为什么某些振动模式比其他振动模式得到更多增强的简单示意图。

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