Characterization by scanning tunneling microscopy of the oxygen induced restructuring of Au(111)

The morphology of the Au(111) surface exposed to oxygen under high pressure (p(o2) = 1 bar) and high temperature (500 less than or equal to T less than or equal to 800 degrees C) during a prolonged period of time (between 1/2 and 24 h) was investigated by scanning tunneling microscopy (STM). At the atomic scale the surface exhibits a (root 3 x root 3)R30 degrees structure which is ascribed to atomic oxygen being strongly chemisorbed at the gold surface. In addition, on a larger scale, a long-range superstructure with hexagonal symmetry and a periodicity varying between 60 and 80 Angstrom is observed. This superstructure is interpreted as a moire type pattern arising from the periodic height modulation induced at the surface by a small lattice mismatch and a slight rotation between the topmost two gold layers. The long-range superstructure exhibits local distortions which can be explained by the high sensitivity of moire patterns to the exact lattice mismatch and to the rotation angle between the two layers. The observation of small reconstructed areas forming on the Au(111) surface upon chemisorption of oxygen indicates that the restructuring proceeds via a nucleation and growth process.