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.
