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https://hdl.handle.net/2142/21508
Description
Title
Long jumps in surface diffusion on tungsten(211)
Author(s)
Senft, Donna Sue Cowell
Issue Date
1995
Doctoral Committee Chair(s)
Ehrlich, Gert
Department of Study
Materials Science and Engineering
Discipline
Materials Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Physics, Condensed Matter
Engineering, Materials Science
Language
eng
Abstract
The length of the jumps executed by atoms during diffusion is important for understanding atomic transport in crystal growth. Molecular dynamics simulations suggest that atomic jumps longer than a nearest-neighbor spacing should contribute at elevated temperatures. Attempts have been made in the past to deduce the jump length from the prefactor in the Arrhenius plot, but this is quite an uncertain procedure. To establish the possible contribution of long jumps in atomic migration, observations have been made in a field ion microscope of single adatoms on W(211), where diffusion is one-dimensional. Experiments with W, Pd, and Ni adatoms reveal that diffusion obeys a simple Arrhenius relation, with entirely normal prefactors. However, a more definitive way of finding jump lengths is to measure and analyze the distribution function for atomic displacement. Such experiments have been carried out and show that W moves entirely by single jumps, but Ni has occasional double jumps even at the lowest temperature examined. These double jumps make up 6% of the total. As the temperature is increased the number of long jumps for Ni is unchanged, while Pd shows a large increase in the numbers of long jumps. At 133 K, jumps spanning two nearest-neighbor distances make up 15% of the total jumps for palladium, and jumps spanning three nearest-neighbor distances make up 12% of the total. These results are the first indication of long jumps in one-dimensional diffusion.
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