Disordering of small metal particles in a scanning transmission electron microscope

Small metal particles in the range of a few nanometers in diameter are seen to progressively disorder when the 100 keV electron beam of a Scanning Transmission Electron Microscope (STEM) is held stationary on the particle. The diffraction pattern of the individual particle is seen to progress from an initial array of indexable diffraction spots to a mixture of diffraction spots and amorphous-like rings and finally to rings with no persistent diffraction spots. Only particles below a critical size are seen to fully disorder. We have observed this disordering in Platinum, Palladium, Rhodium, and Iridium and have developed a model for the disordering process. In this model, electrons scattering from surface atoms transfer enough energy to break the surface atoms from their binding site. A competing process of disordered atoms rebinding to crystalline sites is also included. Because small particles have large fractions of their atoms on the surface, the beam driven disorder, under certain conditions, is able to propagate into the core of the particle. For Platinum, surface disordering requires energy transfers from the electrons to the Platinum atoms of0.54 eV.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2012

Author dc:creator

• Vanfleet, Richard R.

Contributors dc:contributor

• Mochel, J.M.

• Scanning Transmission Electron Microscope (STEM)
• platinum
• palladium
• rhodium
• iridium
• electron scattering in metals
• diffraction patten
• thermodynamics
• small metal particles

Statement dc:rights

• © 1997 Richard R. Vanfleet

Language dc:language

en

Identifier

4048920

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/30770