Macroscopic Materials Built from Ag Nanocrystals

Abstract

Ag nanoparticles are faceted bits of silver metal with diameters on the nanometer length scale. As such, they are another set of building blocks, or ?artificial atoms,? that can be utilized by chemists to create new materials. In our laboratory, we have developed methods to form two materials from Ag nanocrystal precursors. The first material is a thin film, formed at the organic-aqueous liquid interface. Transmission Electron Microscopy (TEM) and Optical Spectroscopy have shown that the film is composed of individual Ag nanocrystals packed as multi-layers. An aqueous phase compound critical to film formation is mercaptoundecanoic acid (MUA), which produces a blue or silvery opalescent film at the organic-aqueous interface. Data and results are presented that explore how the film properties change with varying the identity of the aqueous phase ligand. The second material is created by the controlled evaporation of solvents associated with the film after displacement from the liquid-liquid interfacial region. Amber, micron-sized crystals can be formed by removing the film from the interface and depositing the film on a glass surface, like a Petri dish. We observe these crystals under an optical microscope, and preliminary results from Scanning Tunneling Microscopy (STM) will be presented. Our hypothesis is that these amber crystals are composed of individual Ag nanocrystals, self-assembled into the larger micron-sized structures during solvent evaporation. Our study in the near term is to determine a method for making these amber crystals in a controllable manner and learn about their structural properties.