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Hollow gold nanosphere optical transducers studied using femtosecond time-resolved laser spectroscopy.

机译：使用飞秒时间分辨激光光谱学研究的中空金纳米球光学传感器。

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摘要

This dissertation presents and evaluates the unique interplay between nanoparticle structure, environment, and electronic energy relaxation. This knowledge will provide useful information for tailoring nanoparticle properties so that they can be applied to the development of more efficient transducers, such as a light-harvesting antenna. In particular, plasmonic gold nanoparticles have been synthesized, both hollow (HGNs) and solid (SGNs), and their structural properties have been characterized using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), dynamic light scattering (DLS), and UV/Vis absorption spectrophotometry. Femtosecond pump-probe transient extinction experiments have been conducted on both isolated and aggregated HGNs and SGNs in order to elucidate their electronic energy relaxation properties. While studying how aggregated nanostructures influence optical and electronic properties, an unexpected spectral blue-shift of the surface plasmon resonance (SPR) was observed upon aggregation of HGNs using a salt solution, which led to longer electronic energy relaxation times compared to isolated HGNs. These findings were significant because previous studies have found that SGNs red-shift upon aggregation and have faster electronic energy relaxation times. In order to understand further the nature of the blue shift in HGN aggregates, alkane-thiols were used to induce the aggregation, where it was found that at a critical thickness of the HGN shell, the SPR blue-shifts due to the interaction of the electric fields within the hollow cavities of the nanoparticles. These alkane-thiol ligands provide for more controlled aggregation over the interparticle gap than other aggregating agents such as potassium chloride salt. Transient extinction experiments at high pulse energies were conducted to learn about the modulation in the SPR frequency of HGNs following excitation by a femtosecond laser pulse. The oscillation frequency and phase were determined for a wide range of HGN sizes, revealing a size-dependent excitation mechanism of the vibrational modes. In addition, transient extinction experiments were carried out at low pulse energies in order to determine the electron-phonon coupling times for a wide range of sizes of HGN and SGN samples. As the aspect ratio of the HGN increases, the electron-phonon coupling time decreases (or the electron-phonon coupling increases), whereas for SGNs, the electron-phonon coupling remains constant with increasing diameter. The electron-phonon coupling enhancement exhibited by high aspect ratio HGNs was attributed to the large surface to volume ratio of these structures, which results in non-negligible contributions from their environment. Finally, the phonon-phonon coupling properties of HGNs were investigated, which is the last step in electronic energy relaxation in metal nanoparticles. This study revealed that fluids confined to the hollow core of HGNs have different properties compared to their bulk counterparts, thereby influencing the particle-to-surroundings energy transfer rates. Hence, the cavity influences the electronic and mechanical properties of the HGNs. The structural, optical, and electronic studies on the aforementioned types of metal nanoparticles provide the basis to understand how the surface plasmons influence light absorption in a nearby molecule. Specifically, how the surface plasmons of HGNs and their aggregates interact with the discrete electric-dipole transitions of iron porphyrin molecules. Surface-enhanced Raman spectroscopy (SERS) of iron porphyrin molecules near SGN and HGN aggregate surfaces was employed to understand the interaction between the strong electric fields of HGNs and molecular electronic transitions.
机译：本文提出并评价了纳米颗粒结构，环境与电子能量弛豫之间的独特相互作用。这些知识将为定制纳米粒子的特性提供有用的信息，以便将它们应用于开发更高效的换能器，例如集光天线。特别是，已经合成了中空（HGN）和固体（SGN）的等离子体金纳米颗粒，并使用透射电子显微镜（TEM），能量色散光谱（EDS），动态光散射（DLS）表征了其结构性质，和紫外/可见吸收分光光度法。飞秒泵浦探针瞬态消光实验已经在隔离的和聚集的HGN和SGN上进行，以阐明其电子能量弛豫特性。在研究聚集的纳米结构如何影响光学和电子性能时，使用盐溶液聚集HGN时，观察到了表面等离子体激元共振（SPR）的意外光谱蓝移，与分离的HGN相比，这导致更长的电子能量弛豫时间。这些发现意义重大，因为先前的研究已经发现SGN在聚集时会发生红移，并且具有更快的电子能量弛豫时间。为了进一步了解HGN聚集体蓝移的性质，使用链烷硫醇诱导聚集，其中发现在HGN壳的临界厚度处，SPR蓝移归因于HGN壳层的相互作用。纳米粒子的空心腔内的电场。与其他聚集剂（如氯化钾盐）相比，这些烷烃-硫醇配体在颗粒间间隙上提供了更可控的聚集。进行了高脉冲能量下的瞬态消光实验，以了解飞秒激光脉冲激发后HGN的SPR频率的调制。确定了大范围HGN尺寸的振荡频率和相位，揭示了振动模式的尺寸相关激励机制。此外，为了确定各种尺寸的HGN和SGN样品的电子-声子耦合时间，在低脉冲能量下进行了瞬态消光实验。随着HGN的纵横比增加，电子-声子耦合时间减少（或电子-声子耦合增加），而对于SGN，电子-声子耦合随直径增加而保持恒定。高纵横比HGNs表现出的电子-声子耦合增强归因于这些结构的较大的表面体积比，这导致其环境的贡献不可忽略。最后，研究了HGNs的声子-声子耦合特性，这是金属纳米粒子中电子能量弛豫的最后一步。这项研究表明，与大体积的同类流体相比，局限于HGNs的空心流体具有不同的特性，从而影响了颗粒到周围的能量传输速率。因此，空腔会影响HGN的电子和机械性能。对上述类型的金属纳米粒子的结构，光学和电子研究为了解表面等离子体激元如何影响附近分子的光吸收提供了基础。具体来说，HGNs的表面等离子体激元及其聚集体如何与卟啉铁分子的离散电偶极跃迁相互作用。 SGN和HGN聚集体表面附近的铁卟啉分子的表面增强拉曼光谱（SERS）用于了解HGNs的强电场与分子电子跃迁之间的相互作用。

著录项

  • 作者

    Dowgiallo, Anne-Marie.;

  • 作者单位

    The Florida State University.;

  • 授予单位 The Florida State University.;
  • 学科 Chemistry Physical.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 156 p.
  • 总页数 156
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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