THE STRUCTURE OF CU(110) (2X3)-N - PSEUDO-SQUARE RECONSTRUCTION OF A RECTANGULAR MESH SUBSTRATE

The structure of the Cu(110)(2 x 3)-N phase has been investigated by parallel studies using 3-keV Li+ and 2-keV He+ ion scattering and scanned energy mode normal emission N 1s photoelectron diffraction. The Li+ ion scattering results provide clear evidence for an adsorbate-induced reconstruction of the Cu surface and, in particular, indicate a shortening of the Cu-Cu atomic spacing along the <100> azimuth to a value of 2.7 +/- 0.1 angstrom, similar to the <110> spacing of 2.55 angstrom. A model of the surface consistent with this result involves a pseudo-square Cu top atom layer with N atoms occupying alternate hollow sites leading to a local structure which is a 6% distorted Cu(100)c(2 x 2)-N phase. He+ ion scattering data provides support for the N hollow adsorption sites. Scanned energy mode photoelectron diffraction is insensitive to the nature of the reconstruction but provides information on the local adsorption sites and, hence, on the lateral registry of the reconstructed overlayer and the underlying substrate.