OXYGEN-INDUCED RESTRUCTURING OF AG(111)

Interaction of oxygen with Ag(111) surfaces at atmospheric pressure and at a temperature > 800 K leads to the activated formation of a new phase with long-rangeorder exhibiting periodicities of about 70 angstrom in the [112] direction and 40 angstrom in the [110BAR] direction and a slight rotation by about 2-degrees with respect to the substrate lattice, as probed by means of scanning tunneling microscopy (STM), reflection electron microscopy (REM), and reflection high energy electron diffraction (RHEED). The incorporation of oxygen atoms in subsurface sites causes a slight expansion of the topmost layer by about 3% which accounts for the formation of the observed moire pattern. The superstructure is readily removed by reducing agents.