SUBLATTICE DISORDERING (PREROUGHENING) AND ROUGHENING IN NON-RECONSTRUCTING FCC (110) SURFACES

An anisotropic body-centred solid-on-solid model of the (110) surface (previously studied for the case of reconstructed Au(110)) is examined for the description of the non-reconstructed f.c.c. metal surfaces. A preroughening-type order-disorder phase transition associated with th e in-plane two-sublattice degrees of freedom is detected by means of a Monte Carlo simulation. It takes place about 20% below the roughening transition temperature with parameters chosen to describe roughly the case of Ag(110). This sublattice disordering transition presents nove l critical exponents (including alpha = - 0.23 +/- 0.12 and beta = 0.2 5 +/- 0.08) which differ significantly from those of the 2D Ising mode l. Simulation of the scattering intensities suggests a possible experi mental verification of the proposed phase structure.