Synthesis and Optical Properties of Complex Metal Nanostructures

摘要 9625151 Foss 这个职业计划的总体研究目标是合成足够均匀和复杂的金属颗粒，使它们产生迄今为止在金属颗粒复合材料中看不到的光学行为。这个项目有意针对那些尺寸介于ca. 5纳米（nm）和50 nm。在这些范围内的金属颗粒包含足够数量的原子，以便具有整体光学性质，但足够小，使得它们不会在可见光和更长波长处明显散射光。合成工作将特别关注三种基本结构类型：1）由两种或更多种不同元素亚基组成的圆柱形颗粒; 2）支化金属纳米结构; 3）手性纳米结构。1型颗粒将通过模板合成制备，其涉及将金属电沉积到阳极氧化铝膜的孔中。模板合成方法将允许电化学控制圆柱体半径和长度，以及组成圆柱体的不同金属层的顺序。类型2颗粒将以与类型1类似的方式制备，不同之处在于阳极氧化铝膜将使用产生分支孔结构的电压降低方案生长。手性结构的制备（类型3）将涉及金和其它金属在通过模板合成制备的纳米级银柱基底上的真空沉积（以掠入射）。银基底的氧化将促进手性颗粒释放到溶液中。所有颗粒的结构表征将涉及透射电子显微镜（TEM）和/或原子力显微镜（AFM）。 将对所有三种类型的粒子进行紫外/可见光和近红外（NIR）光谱研究，以评估粒子结构与等离子体共振吸收之间的关系。还将评估含有已制备为缺乏反转对称性的类型1和2的取向颗粒的复合材料的体二次谐波产生（SHG）。含有3型粒子的溶液预计将表现出光学活性，因此将使用圆二色性（CD）光谱进行检查。 这个项目关注的是模板合成方法的应用，以制备前所未有的几何形状和成分复杂的纳米金属颗粒。由于它们的复杂性，这些粒子预计将表现出通常被认为是分子实体的唯一领域的光学行为。该项目将导致更详细地了解金属颗粒结构和复合材料光学性能之间的关系。此外，由于一些预期的性质以前没有观察到来自总颗粒不对称性，该项目也可能导致纳米级金属颗粒的新应用。相关地，由于所提出的合成策略主要基于化学和电化学方法（与光和电子束光刻相反），因此它们将容易地被许多研究小组获得。

Abstract 9625151 Foss The general research goal of this Career proposal is to synthesize metal particles of sufficient uniformity and complexity such that they engender optical behaviors heretofore unseen in metal particle composite materials. This project deliberately targets particles whose dimensions lie between ca. 5 nanometers (nm) and 50 nm. Metal particles within these limits contain a sufficient number of atoms so as to possess bulk optical properties, but are small enough that they do not scatter appreciably light at visible and longer wavelengths. The synthetic work will focus specifically on three basic structural types: 1) cylindrical particles composed of two or more different elemental subunits; 2) branched metal nanostructures; and 3) chiral nanostructures. Type 1 particles will be prepared via template synthesis, which involves the electrodeposition of metals into the pores of anodic aluminum oxide films. The template synthesis method will allow for electrochemical control of both cylinder radius and length, as well as the sequence of the different metal layers of which the cylinder is composed. Type 2 particles will be prepared in similar fashion to type 1, except that the anodic alumina films will be grown using a voltage reduction regime that produces branched pore structures. The preparation of chiral structures (Type 3) will involve the vacuum deposition (at grazing incidence) of gold and other metals onto nanoscopic silver post substrates prepared via template synthesis. Oxidation of the silver foundation will facilitate release of the chiral particles into solution. Structural characterization of all particles will involve transmission electron microscopy (TEM) and/or atomic force microscopy (AFM). UV/Visible and near-infrared (NIR) spectroscopic studies of particles in all three types will be done to assess the relationship between particle structure and plasmon resonance absorption. Composite materials containing oriented particles of types 1 and 2 which have been prepared so as to lack inversion symmetry will also be evaluated for bulk second harmonic generation (SHG). Solutions containing type 3 particles are expected to exhibit optical activity, and will thus be examined using circular dichroism (CD) spectroscopy. %%% This project is concerned with the application of template synthesis methods to prepare nanoscopic metal particles of unprecedented geometric and compositional complexity. By virtue of their complexity, these particles are expected to exhibit optical behaviors that are normally considered the sole province of molecular entities. The project will lead to a more detailed understanding of the relationship between metal particle structure and composite optical properties. Furthermore, as some of the anticipated properties have not been observed previously to arise from gross particle asymmetry, this project may also lead to new applications of nanoscopic metal particles. Relatedly, since the proposed synthetic strategies are based primarily on chemical and electrochemical methods (as opposed to photo- and electron beam lithographies), they will be easily available to many research groups.