IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Wednesday Sessions
       Session SS2-WeM

Paper SS2-WeM2
Surface Phase Transitions of Pt(110) Studied by Desorption Dynamics of Product CO@sub 2@ in Steady-state CO Oxidation

Wednesday, October 31, 2001, 8:40 am, Room 121

Session: Surface Reactions on Metals
Presenter: I. Rzeznicka, Hokkaido University, Japan
Authors: I. Rzeznicka, Hokkaido University, Japan
M.G. Moula, Hokkaido University, Japan
T. Matsushima, Hokkaido University, Japan
Correspondent: Click to Email
This paper reports the first confirmation of the transition from (1x2) to (1x1) through angular distribution analysis of desorbing product CO@sub 2@. Clear distribution changes were observed in the inhibited region where CO retards its oxidation. The surface phase transition of Pt(110)from (1x1)to(1x2) yields differently-oriented adsorption sites of oxygen. The CO oxidation on these sites induces differently-collimated CO@sub 2@ desorption, since this desorption mostly collimates along the local normal of the site. Both the angular and velocity distributions of desorbing CO@sub 2@ will switch sharply around the transition condition. This phenomenon was examined in steady-state CO oxidation on Pt(110) in a wide range of surface temperature and reactant pressures by means of cross-correlation time-of-flight techniques. In the active region where the surface is covered by O(a), desorbing CO@sub 2@ mostly collimated in a two-directional way along +25° or -25° off the surface normal in the (001) plane. This indicates CO@sub 2@ formation on the declining (111) terraces of the (1x2) form. On the other hand, in the inhibited region where the surface is mostly covered by CO(a), the normally directed desorption was sharply enhanced at a critical CO pressure where the two-directional components were suppressed. Below 3x10@super -4@ Torr of fixed O@sub 2@, this critical pressure shifted from the kinetic transition pressure (where the inhibition by CO starts) to higher values with increasing surface temperature. This critical point was confirmed to indicate the completion of the phase transition from LEED and CO adsorption measurements.