Compressed Co Overlayers on Pt(111) Evidence for Tilted Co Species at High Coverages by Digital ESDIAD (Electron Stimulated Desorption Ion Angular Distribution)

摘要

The existence of tilted carbon monoxide molecules in compressed carbon monoxide overlayers on Platinum(111) has been detected using the digital ESDIAD method with enhanced resolution achieved by applying a retarding potential procedure to separate CO(+), CO*, and O(+)ESD products. Digital symmetrization was used for analysis of the ESDIAD data collected under field-free conditions. The CO tilting is consistent with the building of antiphase domain boundaries of close-parked terminal-CO species. It has been found that CO molecules tilt about 6 degs. off-normal at Co coverages higher than 0.6 CO/Pt. The azimuthal directions (equivalent to (110) of CO tilting indicate that the close-packed CO molecules are repelled along the nearest Pt-Pt neighbor directions. Studies of the thermal broadening of the CO+ ESDIAD pattern due to the tilted-CO molecules have shown that the maximum amplitude of the vibrational motion of the tilted-CO species occurs along the directions normal to the tilting plane. A comparison of the CO(+) and CO* ESDIAD patterns has permitted approximate estimation of the distance of the image plane from the center of the charge for the CO(+) ESD product at the point of its origin. Keywords: Electron stimulated desorption angular distribution; Electron stimulated desorption spectroscopy; Chemisorption; Tilted adsorbate molecules; Adsorbate-adsorbate interactions; Reprints. (aw)