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Local surface structure and composition evolution by Monte Carlo simulations

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Title: Local surface structure and composition evolution by Monte Carlo simulations


1
Local surface structure and composition evolution
by Monte Carlo simulations
Jiebing Sun1, James B. Hannon2, Gary L. Kellogg3,
Karsten Pohl1 1 University of New Hampshire,
Department of Physics, NH 2 T. J. Watson
Research Center, IBM Research Division, NY 3
Sandia National Laboratories, Albuquerque, NM
2
Monte Carlo method
  • Cu-Pd NN bonds favorable
  • A trial move involves swap of element identities
  • Free parameters ? --- NN Cu-Pd bond energy
  • ? --- chemical
    potential
  • Internal energy En?, where n is the total number
    of NN PdCu bonds

3
Terrace concentration over time
  • Constant-NVT simulation
  • Adjust ? to get best fit of simulation with
    experimental data in c1 and c2 to get ?? 25 meV

4
Heterogeneity across a step
  • Thermo-dynamical integration method
  • Entropy S integrating dQ/T with respect
    to temperature and using Boltzmann formula
    SklnW at high temperature
  • Chemical potential ? ?F/ ?N ?E/ ?N -
    T?S/ ?N.
  • Constant- ? VT method
  • Surface region open to a reservoir to
    allow Cu-Pd exchange

5
Chemical potential ? by two methods above
6
Heterogeneity near a step
  • ?? 25 meV
  • Nearly constant chemical potential along each
    single scan line
  • c1 and c2 agree with the experimental data

J. Sun, J. B. Hannon, K. Pohl, G. L. Kellogg, PRB
(in production)
7
A case
  • c3 and c1c2 fixed
  • compute partition of c1 and c2
  • c3 0.33
  • c1c2 0.58
  • ?? - 25 meV
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