LEED observations of oxygen ordering on Cu(110)

LEED observations were used to study oxygen adsorbed on Cu(110) and to follow changes in surface structure produced by 5 min anneals at up to 880 K. Factors determining the surface structure include the surface temperature Ts at exposure, the amount of exposure, and the maximum Ts after exposure. For surfaces exposed at Ts = 83 ± 1 K to between 0.3 and 100 langmuir (L) of room-temperature molecular oxygen, the LEED patterns upon exposure and after anneals are described for the first time in a detailed and systematic way. Upon exposure the surface exhibits a (1 × 1) pattern, although diffuse third-order reflections corresponding to an increase in the [110] dimension of the unit mesh are visible for coverages θ ≳ 0.50. A (3 × 1) pattern, which may be due to a molecular configuration, is seen after annealing at 180 K. After annealing at 330 K or higher, a simple relationship exists between oxygen coverage and surface structure, as inferred from LEED patterns; if θ ≲ 0.50, a (2 × 1) pattern is seen; if 0.50 ≲ θ ≲ 0.67, a superposition of a (2 × 1) and c(6 × 2) pattern is seen; if θ ≅ 0.67, a c(6 × 2) pattern is seen; and if θ ≳ 0.67, a c(6 × 2) pattern with additional reflections is seen. For surfaces exposed at 300 ≲ Ts ≲ 320 K to up to 105 L oxygen, the LEED patterns are similar to those reported by others; here too, however, previously unreported behavior is presented. The observations are interpreted in light of UPS and recent XPS data, which give information regarding the chemical state (atomic or molecular) and amount of the adsorbate.