AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoM

Paper SS2-MoM4
Face Specificity and the Role of Metal Adatoms in Molecular Reorientation at Surfaces

Monday, November 2, 1998, 9:20 am, Room 309

Session: Molecular Adsorbates on Metals
Presenter: N.V. Richardson, University of St. Andrews, Scotland, U.K.
Authors: C.C. Perry, University of Liverpool, United Kingdom
S. Haq, University of Liverpool, United Kingdom
B.G. Frederick, University of Maine
N.V. Richardson, University of St. Andrews, Scotland, U.K.
Correspondent: Click to Email
Using Reflection Absorption Infrared Spectroscopy (RAIRS), the coverage dependent reorientation of the benzoate species on the (110) and (111) faces of copper is compared and contrasted. Whereas on Cu(110), benzoate reorients from flat-lying to upright orientation with increasing coverage, on Cu(111), at all coverages, benzoate is aligned normal to the surface. The formation of periodic, flat-lying copper-benzoate structures has been attributed to the availability of metal adatoms, which differs dramatically between the (111) and (110) faces. We discuss the face specificity of molecular orientation by comparing calculated formation energies of adatom-vacancies from ledges and kink sites on (100), (110), and (111) faces. Further support for this model is given by the evaporation of sodium, either by pre- or post-dosing, onto low coverage benzoate/Cu(111), which induces benzoate to convert from perpendicular to parallel orientation. Likewise, coevaporation of Cu while dosing benzoic acid onto the Cu(111) surface also results in a majority of flat-lying benzoate species. Finally, for adsorption on the p(2x1)O/Cu(110) reconstruction, benzoate occurs only as the upright species, which is consistent with reducing the copper mobility and availability on the (110) face. We therefore suggest the possible role of metal adatoms as a new mechanism in controlling adsorbate orientation, and therefore face specificity, in surface reactions.