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 Title: Structure and melting of small metal particles observed by stem microdiffraction Author(s): Contrata, Walter Doctoral Committee Chair(s): Mochel, J.M. Department / Program: Physics Discipline: Physics Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Physics, Molecular Physics, Condensed Matter Abstract: The structure of solvent deposited (Au, Au-Ag, Pt) and vapor deposited (Cu) metal particles $\approx$10-40 A A was studied by electron microdiffraction in a STEM. A CCD array recorded the microdiffraction patterns with high sensitivity and dynamic range, and low noise Microdiffraction patterns were classified according to whether they had distinct Bragg peaks, or were diffuse. Patterns with distinct Bragg peaks showed low rates of twinning, with an upper bound of $\approx$14 $\pm$ 3% in the case of Au-Ag particles. Diffuse patterns indicate that many of the particles are highly disordered, $\approx$88% in the case of Au particles. The effects of the electron beam on Pt particles were studied further. Crystalline Pt particles up to 40A in diameter become disordered after exposures ranging from less than a second up to 40 minutes. Disordered particles' diffraction patterns were dynamic, with flickers of intensity lasting $\approx$15 msec (the resolution of the video tape). Pt particles on an amorphous C substrate remained disordered $\approx$20 min before recrystallizing. The dynamic nature and persistance of the disordered state are reminiscent of Ajayan and Marks's quasimelting theory. Issue Date: 1992 Type: Text Language: English URI: http://hdl.handle.net/2142/22606 Rights Information: Copyright 1992 Contrata, Walter Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9215799 OCLC Identifier: (UMI)AAI9215799
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