MIXED O- COMPETITION BETWEEN NITROGEN AND OXYGEN RECONSTRUCTIVE INTERACTIONS(N LAYERS ON A RH(110) SURFACE )

Scanning tunneling microscopy and low energy electron diffraction stud ies of mixed O+N layers on Rh(110) reveal a competition between (n x 1 ) N-driven and (1 x 2) O-driven added/missing row reconstructions. At low coverage [001] N-Rh rows prevail, forming islands with a (3 x 1) p eriodicity. At moderate coverage separate (2 x 1)N and (1 x 2)O island s are formed. At high coverage the growing (1 x 2)O islands displace t hose of (2 x 1)N. The structural transformations involve a transition from a structure consisting of separate (2 x 1)N and (1 x 2)O islands to a mixed c(2 x 2) N + O layer on a (1 x 2) reconstructed surface.