AVS 46th International Symposium
    Surface Science Division Monday Sessions
       Session SS1+EM-MoM

Paper SS1+EM-MoM11
Surface Reactions on Cr-doped V@sub 2@O@sub 3@

Monday, October 25, 1999, 11:40 am, Room 606

Session: Chemistry on Oxides
Presenter: D.S. Toledano, Yale University
Authors: D.S. Toledano, Yale University
V.E. Henrich, Yale University
Correspondent: Click to Email
Transition-metal oxides are important as gas sensors due to chemisorption-induced changes in surface conductivity. Conversely, changes in substrate electronic structure may alter surface chemisorption properties. While investigating the effect of metal-insulator transitions in Cr-doped V@sub 2@O@sub 3@ on adsorption, we have observed interesting effects involving surface reduction by CO, as well as differences in adsorption on metallic and insulating substrate phases. (Cr@sub 0.015@V@sub 0.985@)@sub 2@O@sub 3@ exhibits two metal-insulator transitions as a function of temperature; these experiments focus on the insulating phase of single-crystal Cr-V@sub 2@O@sub 3@ using UPS, XPS, LEED and AES. When insulating-phase Cr-V@sub 2@O@sub 3@ (0001) is exposed to CO at 273K, CO appears to adsorb dissociatively up to 10@super 3@ Langmuir. Higher exposures result in a C-containing species, and electron transfer to V cations at energies near E@sub F@; decreased occupation of non-bonding O orbitals is also observed. Heating to 470K desorbs this species, but the surface is further reduced after desorption, with increased charge transfer to V cations. Exposure of a CO-reduced surface to O@sub 2@ does not reoxidize the surface or restore the original electronic structure, but appears to result in adsorbed O@super -@ or (O@sub2@)@super -@ which does not re-enter the lattice unless annealed above 700K. CO adsorption on metallic-phase Cr-V@sub 2@O@sub 3@ differs from that on the insulating phase for intermediate exposures, exhibiting higher initial sticking coefficient and desorption temperature; however, the two phases behave similarly for high CO exposures. Adsorption of H@sub 2@O, SO@sub 2@ and O@sub 2@ on both substrate phases has also been studied. This work was partially funded by NSF grant CTS-96-10140