THE STRUCTURE OF THE PT(110)1X2 SURFACE AND ITS 1X2-REVERSIBLE-ARROW-1X1 STRUCTURAL TRANSITION .2. RHEED FROM THE NONPERIODIC PART OF THE STRUCTURE

Abstract

The 1 x 2 missing-row structure of the Pt(110) surface and its structural 1 x 2 half arrow right over half arrow left 1 x 1 order-disorder transition were investigated using RHEED. Part I of the publication dealt with the periodic part of the structure. It was investigated by dynamical evaluation of rocking curves measured at 25 different crystal temperatures between 300 and 1200 K. In this part, the non-periodic part of the structure is studied by analyzing the diffuse RHEED around the half order reflections. The diffuse scattering is evaluated dynamically. We use a formalism in which the scattering arises from transitions between scattering states in the periodic part of the potential and the non-periodic part is the perturbation. For temperatures up to approximately 20 K above the critical temperature T(c) = 855 K of the 1 x 2 half arrow right over half arrow left 1 x 1 transition, the surface is mainly flat. Lengths for the short range order are obtained along and normal to the closed packed [110BAR] atomic chains. These lengths indicate strongly anisotropic order and seem to be characteristic for the transition below T(c). Furthermore, the data suggest an increasing surface roughness about some 10 K above T(c). The initial step formation is dominated by steps with large (111)-facets while at more elevated temperatures also steps with smaller facets appear with increasing probability. These results are consistent with the findings in part I [Surf. Sci. 271 (1992) 616] for the periodic part of the structure.