Structure and melting of small metal particles observed by stem microdiffraction
Contrata, Walter
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https://hdl.handle.net/2142/23885
Description
Title
Structure and melting of small metal particles observed by stem microdiffraction
Author(s)
Contrata, Walter
Issue Date
1992
Doctoral Committee Chair(s)
Mochel, J.M.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
small metal particles
electron microdiffraction STEM
Bragg peaks
structure of deposited metal particles
Language
en
Abstract
The structure of solvent deposited (Au, Au-Ag, Pt) and vapor deposited (Cu) metal particles •1040 Awas swdied by electron microdiffraction in a S1EM. A CCD array recorded the microdiffraction pattems with
high sensitivity and dynamic range, and low noise Microdiffraction pattems 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 •14±3% in the case of Au-Ag particles. Diffuse patterns indicate that many of the
particles are highly disordered, •88% in the case of Au particles. The effects of the electron beam on Pt particles
were sllldied further. Crystalline Pt particles up to 40 A in diameter became disordered after exposures ranging
from less than a second up to 40 minutes. Disordered particles' diffraction patterns were dynamic, with flickers of
intensity lasting •15 msec (the resolution of the video tape). Pt particles on an amorphous C substrate remained
disordered ... 20 min before recrystallizing. The dynamic nature and persistance of the disordered state are
reminiscent of Ajayan and Marks's quasimelting theory.
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