Diffusion of Cu adatoms and dimers on Cu(111) and Ag(111) surfaces is
analyzed basing on ab-initio surface potentials. As compared to the simple
single adatom jumps that alternate between two states, dimers undergo more
complex diffusion process that combines translational and rotational moves.
Diffusion coefficients for these processes on both surfaces are calculated and
compared with diffusion of single particle. The main parameters of diffusion
coefficient: energy barrier and prefactor become temperature dependent when
dimer moves jumping between many positions of different values of energy. Small
difference in the surface lattice constant for Cu and Ag crystal results in
completely different energy landscape for dimer jumps and as an effect
different diffusion process. At the same time single adatom diffusion does not
change so much
We analyze a system of particles diffusing over an anisotropic crystal surface represented as a lattice gas model. Every second row of adsorption sites has higher energy and the diffusion across rows occurs via metastable states. Double occupancy is forbidden and nearest neighbors along rows interact via repulsive or attractive couplings. A collective diffusion coefficient is derived within the framework of a variational approach. Analytic expressions are investigated as functions of metastable state energies, activation energies, interaction parameters and particle density. It is shown that the interactions of particles that reside at stable or metastable sites change the diffusion over the surface. For some parameters the diffusion coefficients along or across rows are totally changed due to the interactions between particles. Diffusion along rows can be amplified or suppressed by the particle density change for different values of the jump activation energies.
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