STRUCTURE AND PHASES OF THE AU(001) SURFACE - INPLANE STRUCTURE

We present the results of an x-ray-scattering study of the structure and phases of the clean Au(001) surface between room temperature and the bulk melting temperature of 1337 K. These experiments were performed in the glancing-incidence geometry, using an ultrahigh-vacuum apparatus for x-ray surface scattering. Three distinct surface structural phases have been identified. In the high-temperature phase (1170<T<1337 K), the x-ray-diffraction pattern has the (1×1) symmetry of the bulk, consistent with a disordered surface layer. At about T=1170 K there is a reversible phase transition to an incommensurate, distorted-hexagonal structure. Below T=970 K the surface has a rotated, distorted-hexagonal structure in which both the incommensurability and the average rotation angle are weakly temperature dependent. In this phase the line shapes of the hexagonal diffraction peaks show hysteresis, and the length scale over which there exists in-plane order is reduced. © 1990 The American Physical Society.