Phase transitions in Yb/Si(111) and Sm/Si(111) film structures

The initial stages in the formation of Yb/Si(1 1 1) and Sm/Si(1 1 1) interfaces were studied by a variety,of experimental methods. An adsorbate submonolayer consisting of two-dimensional domains was found to form on the Si surface in a wide temperature range. The domain structure depends on rare-earth surface density and varies discretely. The nucleation of 3 x 2 domains in two-dimensional vapor and subsequent;transitions to denser reconstructions constitute a series of first-order phase transitions. The coverage dependence of the activation energy for desorption is examined. A model is proposed for explaining the sharp increase in the binding energy between-the adsorbed rare-earth atoms and Si surface upon the 2D vapor --> 3 x 2 domain transition. It is Suggested that the phase transition and domain formation can-he thought of as self-organization of the system.