IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Thursday Sessions
       Session SS1-ThP

Paper SS1-ThP5
Oxygen Defect Structures and Diffusion of Surface Oxygen Atoms on CeO@sub 2@(111) Surface Studied by Noncontact Atomic Force Microscopy

Thursday, November 1, 2001, 5:30 pm, Room 134/135

Session: Catalysis on Model Systems Poster Session
Presenter: Y. Namai, The University of Tokyo, Japan
Authors: Y. Namai, The University of Tokyo, Japan
K. Fukui, The University of Tokyo, Japan
Y. Iwasawa, The University of Tokyo, Japan
Correspondent: Click to Email
CeO@sub 2@ is widely used as a component of automobile catalysts, where CeO@sub x@ (x@<=@2) is believed to work as a buffer of active oxygen of the catalysts to the most efficient region for oxidation of CO and hydrocarbons in exhaust gas. Migration of surface oxygen atoms to active sites for the oxidation and surface structural changes in the reduction-oxidation cycles are crucial issues to understand the role of CeO@sub x@ in an atomic scale. Noncontact Atomic Force Microscopy (NC-AFM) is a recently developed technique to visualize surface structures in an atomic scale. We have applied NC-AFM to a CeO@sub 2@(111) surface and succeeded in obtaining atom-resolved images for the first time. By annealing an Ar ion-sputtered CeO@sub 2@(111) surface at 1173 K for 1 min, hexagonally arranged oxygen atoms with a constant separation of 0.38 nm were observed by NC-AFM. Oxygen point vacancies were found on the surface as dark depressions. Further annealing of the surface at 1173 K in vacuum increased the density of point vacancies and multiple defects began to appear from total annealing period of 4 min. Triangular defects which consist of neighboring three oxygen vacancies and line defects which consist of 2-4 oxygen vacancies along the [10-1] direction, the [0-11] direction, and the [1-10] direction were visualized by NC-AFM. Successive NC-AFM observation revealed that oxygen atoms on slightly reduced CeO@sub 2@(111) surfaces are mobile even at room temperature. Mobility of the surface oxygen atoms seems to depend on the density of surface oxygen defects. Such mobile oxygen atoms may be a key species in the oxidation reactions.