In order to optimize the proparation of surface nanostructures, it is needful to understand microscopic mechanisms of their formation. While in the case of reconstructed semiconductor surfaces the existence of periodic cells of reconstruction is important, in metal hetoroepitaxy mechanism of self-organization is crucial. In particular in the case of nanostructures composed from two bulk immiscible components, there may be a pattern selection due to the competition between strain caused by misfit and chemical interaction preferring phase separation. The resulting surface morphology depends on the symmetry of the surface. On surfaces with (100), or (110) orientation, stable morphology with alternating stripes of different components is possible. On surface with the orientation (111), island-like morphology is expected. We study the pattern formation in 2D alloy on the (100) simple cubic, and on the fcc(111) surfaces. We employ the model of a ternary system of two adsorbates with opposite misfit relative to the substrate, and symmetric binding interaction between components modelled by the simple pair potential [1]. We investigated the dependence of surface patterns on misfit, and interaction between species using off-lattice kinetic Monte Carlo simulations. We considered the regime when the interaction between different species is weaker than interaction between species of the same type. We found that in the equilibrium conditions the system relaxes to a stable configuration with selected size of surface patterns. Stripes of variable width has been observed in the case (100) orientation [1]. Whereas, a set of islands composed from larger particles in the see of smaller particles is self-organized on the fcc(111) surface. The average size of island as well as the time of relaxation is decreasing with the increasing misfit. Non-equilibrium growth leads to intermixing with the frozen ramified islands for both surface orientations.
[1] T. Volkmann, F. Much, M. Biehl, M. Kotrla: Interplay of strain relaxation and chemically induced diffusion barriers: Nanostructure formation in 2D alloys, Surf. Sci. 582, 157 (2005).
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