Structure and Dynamics in Ligand-Protected and Supported Metal Nanoparticles
Menard, Laurent D., Jr
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https://hdl.handle.net/2142/87889
Description
Title
Structure and Dynamics in Ligand-Protected and Supported Metal Nanoparticles
Author(s)
Menard, Laurent D., Jr
Issue Date
2006
Doctoral Committee Chair(s)
Nuzzo, Ralph G.
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Language
eng
Abstract
This dissertation describes the use of x-ray absorption spectroscopy (XAS) and advanced electron microscopy methods to develop fundamental understandings of nanoparticle structure. Analysis of the x-ray absorption spectra provides structural information with 0.001 A precision. Quantitative high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) measurements characterize metal clusters and nanoparticles on the basis of the number of metal atoms they contain. Ligand-protected 13-atom gold clusters serve as a model system to illustrate the capabilities of a correlated use of these techniques. They exhibit a molecular density of electronic states and non-bulk icosahedral structure. These gold clusters are further used as precursor in the preparation of titania-supported gold oxidation catalysts via ligand removal using ozone or thermal treatments. The capability of the quantitative HAADF-STEM analysis for the determination of nanoparticle shape is demonstrated in these studies. X-ray absorption spectroscopy studies of sub-nanometer gamma-alumina-supported platinum nanoparticles revealed unprecedented metal-metal bond contraction with increasing temperature. Both the structural and electronic information obtained in the spectroscopic studies suggest that support-particle charge transfer is responsible for these dynamic effects. Supported bimetallic iridium-platinum nanoparticles were also prepared via reduction of a bimetallic cluster precursor. This preparation allowed excellent control of nanoparticle size and compositional distributions as the stoichiometry of the cluster precursor was retained. This was confirmed analytically using energy dispersive x-ray (EDX) spectroscopy of individual nanoparticles. XAS studies revealed that the bimetallic nanoparticles assumed a core-shell structure with an iridium-rich core and a platinum-rich shell. The implementation of a novel analysis method that accounted for the overlap of the iridium and platinum absorption edges allowed the determination of structural parameters with low uncertainties and a consequently well-characterized structural model.
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