Solid-on-solid model of overlayer-induced faceting

Abstract

A solid-on-solid model is proposed to describe faceting of bcc(111) metal surface induced by a metal overlayer. It is shown that the first order phase transition occurs between faceted {211} or {110} and disordered phases. The ordered phases consist of large 3-sided pyramids with {211} facets or {110} facets. It is shown that the high-temperature disordered phase has not planar bcc(111) structure but faceted disordered structure. Hysteresis effects were observed when the system was warmed above the transition temperature and then cooled down. Temperature dependence of LEED patterns for faceted and disordered phase are calculated in kinematic approximation.

Simulation of adsorbate-induced faceting on curved surfaces

“…It has been shown that the energy of the (2 1 1) face is minimal when À2 < K < 0, whereas the (1 1 1) surface is stable for K > 0. Therefore simulations of a flat SOS model [27] with negative K (e.g., K = À1.25) show faceting of a bcc (1 1 1) surface. In the present model, energy of a spherical surface E sp decreases with h for negative K but is still greater than the energy of a (2 1 1) face, e.g., energies per column for K = À1.25 are: E 111 = 7, E sp (h = 20°) = 6.26 and E 211 = 5.75.…”

“…Model parameters J 0 , J 1 , J 2 , K 1 , and K 2 can be expressed by interaction energies between substrate and adsorbate atoms (for details see [27]). …”

“…[27] it has been shown that energies per column of ideal faces (1 1 1), (2 1 1), and (1 1 0) are the same for the interactions limited to the nearest neighbours. It turns out that the same is true for the energy of a spherical surface.…”

“…For this reason we can limit the number of the model parameters to two (J 2 , K 2 ). Similarly as in [27], we can eliminate one more parameter by choosing J 2 as the unit of energy. We will work with dimensionless quantities: energy e H ¼ H =J 2 , temperature e T ¼ k B T =J 2 , and interaction constant K = K 2 /J 2 (in what follows, the tilde will be omitted).…”

“…In our earlier paper [27] we have proposed a SOS model to study the adsorbate-induced faceting of the bcc(1 1 1) crystal surface at constant coverage. Monte Carlo simulation results show formation of pyramidal facets in accordance with experimental observations.…”