LEED CRYSTALLOGRAPHIC STUDIES FOR THE CU(110)-(2 X 3)-N SURFACE-STRUCTURE

An initial multiple-scattering analysis of LEED intensities has been performed for the Cu(110)-(2 x 3)-N surface structure. R-factor analysis supports neither simple N overlayer models nor models with Cu(100)-type top-layer reconstructions. The best correspondence between calculated and experimental intensities appears with models where every other [001] row is missing, similar to that observed for the Cu(110)-(2 x 1)-O surface. The favoured surface structure has N atoms chemisorbed on long-bridge sites such that chains of (Cu(a)-N-Cu(b)-N-Cu(a))x create a surface analogous to the ideal Cu3N(110) surface, except that every third N atom is missing from the surface chains. There is evidence that lateral displacement of copper atoms from the ideal positions leads to two different N-Cu surface bond lengths with values near 1.83 and 1.90 angstrom. Each N atom also bonds to two Cu atoms in the second layer with equal bond lengths of about 1.88 angstrom.