LEED investigations on Co(0001):: the (√3 x √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 (root 3 x root 3)R30 degrees-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 Angstrom outwards. The optimum length for the CO bond is 1.17 +/- 0.06 Angstrom and that for the C-Co distance 1.78 +/- 0.06 Angstrom. The first-layer Co-Co distance is 2.04 Angstrom and thus only slightly expanded from the bulk value. The structure obtained is compared with other known CO structures on transition metals. (C) 2000 Elsevier Science B.V. All rights reserved.