Abstract
The CO-induced restructuring of Co(11–20) has been investigated with temperature-programmed desorption (TPD), low-energy electron diffraction, scanning tunneling microscopy (STM), and density functional theory. CO induces a (3 × 1) surface reconstruction at room temperature, involving the anisotropic migration of Co atoms as uncovered by STM. The TPD investigations of the unreconstructed and reconstructed surface through exposure to CO at 100 K and room temperature, respectively, showed a slightly lower desorption peak temperature for the unreconstructed surface. Based on the STM observations, two theoretical model surfaces with (3 × 1) periodicity were investigated and compared to the unreconstructed surface, one with a missing and one with an added, [0001]-directed, zigzag row of Co atoms. The calculated adsorption energies infer that the added row structure is the energetically preferred surface under CO exposure. The most favorable adsorption energies were found for 4 CO coordinated to the added (topmost) row of the model surface, with the largest difference to the unreconstructed surface. Calculations of transition states yielded a significant energy barrier for removing Co from the topmost, unreconstructed layer of the hcp packing. The initial restructuring occurred preferentially through a carbonyl-type species where the migrating Co atom was bonded to two CO molecules.