AVS 49th International Symposium
    Surface Science Monday Sessions
       Session SS2-MoA

Paper SS2-MoA8
Nucleation and Sintering Kinetics of Pd on @alpha@-Al@sub 2@O@sub 3@(0001)

Monday, November 4, 2002, 4:20 pm, Room C-110

Session: Nucleation & Growth of Metals on Oxides & Semiconductors
Presenter: S.L. Tait, Jr., University of Washington
Authors: S.L. Tait, Jr., University of Washington
L.T. Ngo, University of Washington
Q. Yu, University of Washington
S.C. Fain, Jr., University of Washington
C.T. Campbell, University of Washington
Correspondent: Click to Email
Low-temperature methane combustion for applications in electric generator turbines is catalyzed by Pd nanoparticles to minimize NO@sub x@ pollution. The reaction depends on the dissociation of methane molecules on the Pd surface. Nanoscale Pd particles contain coordinatively unsaturated Pd atoms, making them more active for the dissociation of CH@sub 4@. We have studied the growth of Pd nanoparticles on the @alpha@-Al@sub 2@O@sub 3@(0001) surface. The alumina single crystal was cleaned by annealing in air and in vacuum. The cleanliness and structure of the surface were verified by XPS and LEED. Experiments were conducted on the unreconstructed 1x1 and the reconstructed @sr@31x@sr@31 R±8.9° surfaces. Wide terraces were observed on the surface with non-contact atomic force microscopy (NC-AFM). Sub-monolayer doses of Pd were deposited by vapor deposition. NC-AFM was used to observe the growth of Pd nanoparticles upon annealing. These measurements provide information about the Pd particle size, number density and morphology. The Pd showed a tendency to cluster at step edges. To measure Pd particle sintering kinetics and size effects thereon, temperature-programmed ion scattering spectroscopy was used to monitor the fraction of the surface covered by Pd particles continuously as the surface was heated at 1 K/s. The number density of the Pd particles was measured before and after heating using NC-AFM. Curiously, large regions of the surface were found to be void of clusters even at step edges. A mechanism involving the various elementary steps in atom and cluster migration is being developed to model the kinetics of sintering with physically reasonable parameters. Work supported by DOE-OBES Office of Chemical Sciences and the M. J. Murdock Charitable Trust. LTN supported by the IGERT Nanotechnology Fellowship.