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 SS3-ThP

Paper SS3-ThP17
Surface-Termination-Dependence of the Reactivity of Single Crystal Hematite with Carbon Tetrachloride

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

Session: Surface Reactions Poster Session
Presenter: R.M. Osgood, Jr., Columbia University
Authors: N. Camillone III, Columbia University
K. Adib, Columbia University
K.T. Rim, Columbia University
J.P. Fitts, Columbia University
G.W. Flynn, Columbia University
S.A. Joyce, Pacific Northwest National Laboratory
R.M. Osgood, Jr., Columbia University
Correspondent: Click to Email
We describe ultrahigh vacuum Auger electron spectrometric measurements of the uptake of chlorine following the exposure of single crystal hematite to CCl@sub 4@ at room temperature. We compare the surface chemistry of two distinct terminations of @alpha@-Fe@sub 2@O@sub 3@: the Fe@sub 3@O@sub 4@ "selvedge" and the @alpha@-Fe@sub 2@O@sub 3@ / FeO "biphase." For Fe@sub 3@O@sub 4@ (111)-2x2 we estimate that saturation levels of Cl of at least ~ 27 % of a monolayer are attained at relatively low exposures of on the order of 0.1 L. No significant amount of carbon uptake is detected. Low energy electron diffraction measurements suggest that, dependent upon preparation procedures, at least two types of @alpha@-Fe@sub 2@O@sub 3@ / FeO biphase structures can be formed. Interestingly, no significant Cl or C adsorption is detected for either of these biphases, revealing a marked difference in the reactivity of the terminations. Comparison of these results with the surface structure of these terminations suggests that the active site for the dissociative adsorption of CCl@sub 4@ on Fe@sub 3@O@sub 4@ (111)-2x2 must comprise both an iron cation and an oxygen anion that is uncapped by iron cations. Modification of the biphase termination by thermal treatment, as well as the electron-stimulated and thermal desorption of Cl from the saturated Fe@sub 3@O@sub 4@ (111)-2x2 selvedge will be discussed. Finally, the relationship between these results and our recent STM measurements on this system will be presented.