AVS 46th International Symposium
    Surface Science Division Friday Sessions
       Session SS2-FrM

Paper SS2-FrM6
Chemisorption and Dissociation of O@sub 2@ on Pd(111) Studied by STM

Friday, October 29, 1999, 10:00 am, Room 607

Session: Adsorption on Metals and Silicon
Presenter: M. Salmeron, Lawrence Berkeley National Laboratory
Authors: M.K. Rose, Lawrence Berkeley National Laboratory
A. Borg, Norwegian University of Science and Technology, Norway
F. Besenbacher, University of Aarhus, Denmark
D.F. Ogletree, Lawrence Berkeley National Laboratory
M. Salmeron, Lawrence Berkeley National Laboratory
Correspondent: Click to Email
A variable temperature STM study of chemisorption and dissociation of O@sub 2@ on Pd(111) is presented. Adsorption of O@sub 2@ on Pd(111) at 30K in the submonolayer range causes formation of a superoxo like and peroxo like molecular oxygen species. These two species image differently in STM, the superoxide appears to have weaker corrugation as compared to the peroxide. The superoxide is the more mobile species of the two at 30K. The peroxide display (2x2) structure in ordered areas, which grow in size upon annealing to 100K. Induced by the STM tip, individual O@sub 2@ molecules dissociate into pairs with a preferred separation of 2 lattice spacings, which is the equilibrium spacing in the (2x2)-O structure on Pd(111). Thermal O@sub 2@ dissociation is observed at about 150K. Our data show that the oxygen molecules evaporate from the peroxide island periphery onto the terrace before dissociation. Similar atomic oxygen pair spacings are observed in this case, but the distribution of oxygen on the surface is influenced by subsurface species present in the Pd(111).