ORIENTATIONAL PHASE-DIAGRAM OF THE STEPPED AU(001) SURFACE

We report an X-ray scattering study of the structure and morphology of a stepped Au(001) surface between room temperature and bulk melting. At high temperatures, between 1170 and 1220 K, the vicinal Au(001) sur face appears rough. Below T-0 = 1170 K, there is a facetting transitio n: hexagonally reconstructed (001) facets appear in coexistence with u nreconstructed, stepped domains. The tilt angle of the stepped domains increases with decreasing temperature, exhibiting a power-law behavio r versus reduced temperature. The phase behavior of the hexagonally re constructed domains follows that observed on nominally unstepped Au(00 1) surfaces. At T-1 = 992 K, there is a second facetting transition at which the stepped domains reconstruct to form a rotated and corrugate d, quasi-hexagonal structure. The corrugation is threefold commensurat e with the average terrace width, consistent with a 2 degrees magic vi cinal phase. The orientational phase diagram of vicinal Au(001) is ded uced and found to be qualitatively similar to that of vicinal Pt(001), although with intriguing differences. (C) 1998 Elsevier Science B.V. All rights reserved.