AVS 49th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoA

Paper SS1-MoA9
Structural and Chemical Properties of Ti/Pt(100)-c(2x2) Second Layer Alloy - Evidence for Strong Ligand Effects

Monday, November 4, 2002, 4:40 pm, Room C-108

Session: Surface Reactions: CO and NO
Presenter: B.E. Koel, University of Southern California
Authors: S. Hsieh, University of Southern California
T. Matsumoto, University of Southern California
M. Batzill, Tulane University
B.E. Koel, University of Southern California
Correspondent: Click to Email
We have investigated the structure and chemisorption properties of a Ti/Pt(100) surface alloy using AES, XPS, LEED, STM, XPD, ALISS, and TPD of CO and H@sub 2@. Samples were prepared by evaporating Ti onto a clean Pt(100)-hex reconstructed surface at 300 K. After annealing the sample to 800 K, a c(2x2) ordered LEED pattern was observed that sharpened as the temperature was increased to 920 K. Further annealing to 1000 K caused the LEED pattern to become diffuse, due to onset of disorder in the surface layers resulting from Ti diffusion into the bulk. Using XPD and ALISS, we have determined that Ti atoms in the Ti/Pt(100)-c(2x2) surface alloy are not present in the topmost layer, but instead, in the second layer. Thus, the surface layer is pure Pt. XPS results showed that the Ti 2p@sub 3/2@ peak from the surface alloy is shifted about 1.4 eV from a thick Ti film, and the Pt 4f peak is shifted 0.1 eV, consistent with the formation of strong intermetallic bonds upon alloying. CO adsorbed reversibly on the alloy, desorbing in a broad peak with a maximum at 376 K, showing a strong downward shift of 132 K compared to CO desorption from clean Pt(100). Thermal desorption of H@sub 2@ was also studied and a similar peak shift toward lower temperatures was observed. In addition, much less H@sub2@ adsorbed on the Ti/Pt(100)-c(2x2) surface than on Pt(100). These results show that the second-layer Ti atoms exert a strong "ligand effect" on the Pt atoms at the surface, and this is a good model system for studying pure ligand effects at alloy surfaces.