Non-Ising behavior of the Pt(110) surface phase transition

We have investigated the structural transition of the Pt(110)1×2 reconstruction using x-ray diffraction. We find weakening and broadening of the half-order peak with temperature above ${\mathrm{T}}_{\mathrm{c}}$=1080 K, exactly analogous to the Au(110)1×2 surface studied by LEED. Unlike the Au(110) result, however, we find the peak shifts as well, indicating that steps spontaneously appear in Pt(110) above ${\mathrm{T}}_{\mathrm{c}}$. Even though we find good agreement with theoretical 2D Ising exponents, the steps refute classification of this system as a simple two-state model, and favor a roughening description instead.