Atomic motion on the close packed plane of a hexagonally close packed metal
Goldstein, Jonathan Todd
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/18854
Description
Title
Atomic motion on the close packed plane of a hexagonally close packed metal
Author(s)
Goldstein, Jonathan Todd
Issue Date
1996
Doctoral Committee Chair(s)
Ehrlich, Gert
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
single adatom behavior
W adatoms
Re adatoms
Language
en
Abstract
We present, for the first time, an account of single adatom behavior on the
close-packed surface of a hexagonally dose-packed material. Specifically, we
have explored the diffusion and related phenomena of Re and W adatoms on Re
(0001). Prefactors and activation energies to diffusion of 6.13(x2.6±1 )x10-6 cffil. Is,
11.11±.43 kcal/mol and 2.17(x2.7±1)x10-3 cffil/s, 11.04±.34 kcal/mol were
measured for Re and W, respectively. The large difference in prefactor values,
the largest yet seen for two elements on the same surface, contrasts with the
closeness of the activation energies. Furthermore, the activation energies reveal
an intriguing trend. Specifically, rhenium's activation energy to diffusion as well
as the ratio of its activation energy to its heat of vaporization is close to, but
slightly greater than the corresponding quantities for tungsten on Re (0001), Ir
(111), W (110), and W (211). Both Re and W were found to occupy only 1 of the 2
available three-fold hollow surface sites. A minimum energy difference of 2.5±.3
kcal/mol and 2.0±.3 kcal/mol is found between these two sites for Re and W,
respectively. Temperatures for the onset of motion and of dissociation were
measured for Re trimers through octamers. The trend in the temperatures
displays a significant dip for tetramers. Re was not found to localize at the point
of impact upon deposition onto aRe (0001) surface held at 20K. We thus present
the first evidence of transient mobility obtained from direct observations of
single adatoms. To supplement this study of single adatoms, we also have
explored aspects of diffusion in concentrated layers. A Monte Carlo simulation
study was performed in which the diffusivity of a lattice gas with nearestneighbor
exclusion is measured as a function of coverage. Through the physical
mechanism of site-exclusion, the ad-ad interaction affects a diffusivity which
iv
increases with coverage to a maximum at 8 =.1, and then decreases rapidly.
Thermodynamics are found to be the deciding factor in the diffusivity's trend at
low coverages, while the effective jump rate dominates coverages greater than .1.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
