Theoretical description of adatom migration in two-dimensional highly-ordered states
Institute of Physics of the National Academy of Sciences, pr. Nauki 46, 252028, Kiev,
2 Max-Planck-Institut für Eisenforschung, 40074 Düsseldorf, Germany
3 Lehrstuhl für Physikalische Chemie II, Universität Dortmund, 44227 Dortmund, Germany
Published online: 15 May 1999
Analytical expressions for chemical, jump, and tracer diffusion coefficients are obtained for interacting lattice gases on a square lattice. Strongly repulsive nearest neighbor interactions cause the formation of a highly-ordered c(2x2) state in the vicinity of half coverage. It is shown that only strongly correlated successive adatom jumps contribute to the particle flow. This allows to describe the adatom kinetics by considering an almost ideal lattice gas of defects. Two types of defects are considered, adatoms in the empty sublattice and vacancies in the filled sublattice of the c(2x2) ordered state. The diffusion equations for these defects are developed considering the generation and recombination of defects. In addition we have considered adatom transport caused by the motion of defect pairs (dimers). Dimer transport mechanism prevails in the high coverage region. The characteristic features of the various diffusion coefficients near half coverage are analyzed and discussed. The theory is compared with the results of sophisticated Monte-Carlo simulations which have been executed with the use of a fully parallelized algorithm on a Cray T3E (LC784-128). The agreement between theoretical and MC results is excellent if the motion of dimers at is taken into account.
PACS: 82.20.Mj – Nonequilibrium kinetics / 68.35.Fx – Diffusion; interface formation / 64.60.Cn – Order-disorder transformations; statistical mechanics of model systems
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999