LEED investigations on Co(0001): the (3×3)R30°-CO overlayer

The local adsorption structure of CO on Co(0001) has been determined at 160 K using dynamical low-energy electron diffraction (LEED). The CO molecules in the (3×3)R30°-CO overlayer adopt the on-top site with the CO axis perpendicular to the surface and induce buckling in the top Co layer pulling the Co atom beneath the CO by 0.04±0.04 Å outwards. The optimum length for the CO bond is 1.17±0.06 Å and that for the CCo distance 1.78±0.06 Å. The first-layer CoCo distance is 2.04 Å and thus only slightly expanded from the bulk value. The structure obtained is compared with other known CO structures on transition metals.