STRUCTURAL-ANALYSES OF THE C(2X4)-N+2O AND THE (2X1)-N PHASES ON RH(110) BY LOW-ENERGY-ELECTRON DIFFRACTION

The LEED analysis of the Rh(110)-(2 x 1)-N phase supports convincingly the Rh-N-added-row model revealing a Rh-N bond length of 1.91 +/- 0.04 Angstrom. The atomic geometry of c(2 x 4)-N + 20 on Rh(110) reflects the structural elements found in the pure N and O phases: The type of the Rh(110) surface reconstruction is induced by the oxygen adsorption, and a missing-row reconstruction analogous to the Rh(110)-(2 x 2)p2mg-20 surface is observed. Oxygen occupies the threefold-coordinated fee site along the densily-packed rows. Nitrogen, however, causes the O network of the Rh(110)-(2 x 2)p2mg-20 to rearrange in order to provide N-adsorption sites which are maximal apart from the surrounding O atoms and, in addition, retains the local chemisorption geometry as compared with the pure (2 x 1)-N phase. Both requirements are met by shifting every second O-zigzag chain along the [110] direction by a substrate lattice vector and by adsorbing N in the long-bridge site at the bottom of the (1 x 2) troughs.