Phase transitions on reconstructed (110) surfaces

Abstract

The deconstruction transition of the (110) surface of Au and Pt is investigated theoretically. A previous treatment by the same authors is first revisited in the light of recent experiments. Then, a more refined model, based on the transfer matrix formalism, is introduced, which takes into account short-range interaction between steps. For strong attractive interaction a pair of opposite steps is bound to form an Ising domain wall and the system undergoes, upon heating, first an Ising transition and at higher temperature, when the steps unbind, a roughening transition. For weak or repulsive interaction between the opposite steps, when the pair is not bound, a roughening and deconstruction transitions are expected to occur at the same temperature. The Ising and the two roughening transitions merge in the multicritical point. The shift of the superstructure surface peak above the transition is investigated. The ratio shift/width is found to vanish at the transition for an Ising transition, in contrast with experiments on Pt. It is argued that the actual Au and Pt surface phase transitions are very close to the multicritical point.