Abstract

Low-energy electron diffraction (LEED) patterns from CO adsorbed on various faces of Pt indicate that the CO molecule attaches itself with its linear axis normal to the metal surface. Two CO structures (phase H and phase L) form on the (100) face of Pt. Both phases are of rectangular symmetry and occur in domains related by a 90° rotation. The phase present is found to depend on the surface concentration of CO, phase H having a higher coverage ( 3 4 ) than phase L ( 2 3 ) . Phase H has a structre 2 × 4 times the Pt (11) spacing with major axes parallel to the Pt [11] directions. Phase L has a structure 1 × 3 times the Pt (10) spacing with major axes parallel to the Pt [10] directions. The phase L structure indicates a rather strong attractive interaction between certain of the adsorbed CO molecules. At a low ambient CO pressure phase H can be transformed to phase L either thermally at approximately 80° C or by action of the electron beam. This action is shown to arise from electron-adsorbate molecule collisions. The observations are compared with current literature data concerning the removal by electron beams of impurities bound in the lattices of oxides and the removal of chemisorbed species from metal substrates. It is concluded that for moderate to strongly bonded adsorbates the electron beam will have negligible effects on LEED observations, but for lightly bonded species such as physisorbed gases it appears that the effects may be quite large unless a relatively high pressure of the ambient gas can be maintained to supply the back reaction.

Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call