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Structural and chemical characterization of complex nanomaterials at atomic resolution

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Title: Structural and chemical characterization of complex nanomaterials at atomic resolution
Author(s): Sanchez, Sergio I.
Director of Research: Nuzzo, Ralph G.
Doctoral Committee Chair(s): Nuzzo, Ralph G.
Doctoral Committee Member(s): Girolami, Gregory S.; Gewirth, Andrew A.; Zuo, Jian-Min
Department / Program: Chemistry
Discipline: Chemistry
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): Nanomaterials characterization Nanocatalysts Nanostructures Electron microscopy Transition metal nanoparticles Nanocrystals Atomic Pair Distribution Function X-ray diffraction X-ray absorption spectroscopy
Abstract: Catalytic and energetic nanomaterials are analyzed chemically and structurally in atomistic detail. Examination of the prototypical industrial catalyst Pt catalysts supported on γ-Al2O3 using X-ray absorption spectroscopy (XAS) and scanning transmission electron microscopy (STEM) revealed non-bulk-like behavior. Anomalous, temperature-dependent structural dynamics were characterized in the form of negative thermal expansion (NTE) and abnormal levels of disorder. To examine a less complex system, electrocatalytically-active, core-shell nanostructures assembled from Pt and Pd were synthesized and subsequently examined using spherical aberration-corrected STEM (Cs-STEM) and high-energy X-ray diffraction (XRD). Atomically resolved micrographs provide significant insight into the differences in crystallinity and metal-atom bonding between Pt and Pd. The apparent structural dichotomy between Pt and Pd was extended to studying the differences in nanostructure between other third row fcc transition metals (3M – Ir, Pt, and Au) and their second row counterparts (2M – Rh, Pd, and Ag). With the use of Cs-STEM and atomic pair distribution function (PDF) measurements it was determined that the Au, Pt and Ir nanocrystals were more crystalline than their Ag, Pd and Rh analogues and that the 3M series was capable of imparting its crystal structure onto the atoms from the 2M series. Lastly, we looked at highly-reactive Al crystals and their successive passivation by secondary transition metals (Cu, Ni, Ag, Pd, Au and Pt). Rather than affording a uniform, monolayer coverage, Cs-STEM, XRD and energy dispersive X-ray spectroscopy revealed unalloyed, particulate deposits of the secondary metal on the Al.
Issue Date: 2011-05-25
URI: http://hdl.handle.net/2142/24024
Rights Information: Copyright 2011 Sergio I. Sanchez
Date Available in IDEALS: 2011-05-25
Date Deposited: 2011-05
 

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