Structure and melting of small metal particles observed by stem microdiffraction

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2011

Author dc:creator

• Contrata, Walter

Contributors dc:contributor

• Mochel, J.M.

• small metal particles
• electron microdiffraction STEM
• Bragg peaks
• structure of deposited metal particles

Statement dc:rights

• 1992 Walter Contrata

Language dc:language

en

Identifier

3471708

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/23885