AVS 56th International Symposium & Exhibition
    Surface Science Monday Sessions
       Session SS2-MoA

Paper SS2-MoA8
Growth, Composition and Surface Chemistry of Ni-Au Clusters on TiO2(110)

Monday, November 9, 2009, 4:20 pm, Room N

Session: Formation & Reactivity of Nanoclusters
Presenter: D.A. Chen, University of South Carolina
Authors: D.A. Chen, University of South Carolina
S.A. Tenney, University of South Carolina
J.S. Ratliff, University of South Carolina
C.C. Roberts, University of South Carolina
Correspondent: Click to Email
Scanning tunneling microscopy (STM) studies show that bimetallic Ni-Au clusters supported on TiO2(110) are formed by deposition Au on top of Ni clusters. Due to the higher mobility of Au compared to Ni atoms on TiO2(110), deposited Au is nucleated at existing Ni clusters. Low energy ion scattering experiments demonstrate that the surface of the bimetallic clusters is predominantly Au for compositions above 50% Au, but 10-15% Ni also exists at the surface. The presence of Ni at the surface is in contrast to the expected Ni core-Au shell structure based on bulk thermodynamics; the large bulk miscibility gap for the two metals and the lower surface free energy of Au compared to Ni predicts that only Au should be at the cluster surface. Furthermore, adsorption of CO onto the Ni-Au clusters appears to induce the diffusion of Ni to the cluster surface. After annealing the Ni-Au clusters to 800 K and above, the clusters become encapsulated by stoichiometric titania. Although Ni and Au clusters annealed to 1000 K are roughly the same size, the addition of Ni to the Au clusters suppresses cluster sintering.