We have used x-ray-diffraction analysis to examine the structure of flat and vicinal Cu(001) surfaces under the influence of oxygen chemisorption. The initial electropolished vicinal surface consists of a fairly regular array of steps and terraces that preferentially orient the oxygen-induced reconstruction. Prolonged annealing leads to a hill-and-valley morphology with large (001) facets, upon which the preferential orientation is lost, just as for the flat surface. We find evidence for only one ordered phase as a function of oxygen coverage, which has 2 √2 × √2 symmetry. Crystallographic analysis of the diffraction data shows this to be a ‘‘missing-row’’ structure with 25% of the Cu sites vacant and large relaxations in the top layer. The oxygen site is not uniquely determined, however, with two distinct possibilities. This Cu(001)/O structure has a surprising similarity to that proposed for Cu(110)/O. In fact both surfaces can be decomposed into the same basic structural element, which is a Cu-O-Cu chain oriented along bulk [100] directions.

• Received 15 February 1990

DOI:https://doi.org/10.1103/PhysRevB.42.6954