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.

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We propose a lattice gas model to account for linear chain structures adsorbed on (112) faces of tungsten and molybdenum. This model includes a dipole-dipole interaction as well as a long-range indirect (oscillatory) interaction of the form ∼ cos(2kF r + ϕ)/r, where kF is the wavevector of electrons at the corresponding Fermi surface and ϕ is a phase shift. It is assumed that the structures are stabilized by an attractive indirect interaction along the chains.We have explicitly demonstrated that the periodic ground states strongly depend on a competition between the dipole-dipole and long-range indirect interactions.The effect of temperature in our model of linear chain structures is studied within the molecularfield approximation. The numerical results clearly show that for the dipole-dipole interaction only , all long-periodic linear chain phases are suppressed to low temperatures while phases with periods 2, 3, and 4 dominate the phase diagram. However, when the long-range indirect interaction becomes important, the long-periodic linear chain phases start to fill up the phase diagram and develop a high thermal stability.We have chosen model parameters in order to reconstruct a sequence of long-periodic phases (for coverages less than 0.5) as observed experimentally at T = 77K for Li/Mo(112) and Li/W(112). It would be interesting to verify our model and assumptions by checking experimentally the corresponding phase diagrams.

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