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

Paper SS2-MoA6
Controlling Island Size Distributions for Metals on Oxides: Cu and Ni Islands on TiO@sub 2@(110)-(1x2)

Monday, November 4, 2002, 3:40 pm, Room C-110

Session: Nucleation & Growth of Metals on Oxides & Semiconductors
Presenter: D.A. Chen, University of South Carolina
Authors: J. Zhou, University of South Carolina
B.T. Long, University of South Carolina
D.A. Chen, University of South Carolina
Correspondent: Click to Email
Metal islands deposited on oxide surfaces are frequently used as model systems for understanding heterogeneous catalysts. In order to investigate how the surface chemistry of the metal islands may change as a function of island size, it is first necessary to produce islands with narrow size distributions. In these studies, Cu and Ni have been vapor-deposited onto a partially reconstructed TiO@sub 2@(110)-(1x2) surface and characterized by STM under UHV conditions. The key to achieving a uniform island size distribution for Cu on TiO@sub 2@(110)-(1x2) is a low D/F ratio, where D is the diffusion rate for Cu on the surface and F is the Cu deposition or flux rate. When rate of deposition is high relative to diffusion, the incoming Cu atoms have a greater probability of encountering another Cu atom and forming a new island before they are able to diffuse across the surface and contribute to the growth of an existing island; in this case, small islands of uniform sizes are formed with high island densities. When the rate of diffusion is high relative to flux, the incoming Cu atoms are more likely to diffuse to an existing island before encountering other Cu atoms; in this case, Cu islands of varying sizes with lower island densities are formed. We have varied the D/F ratio by changing both the deposition rate and the temperature of the surface during deposition. In all cases, the lower D/F ratio yields a more uniform size distribution. Notably, the Cu islands grown on this partially reconstructed TiO@sub 2@(110)-(1x2) surface produce high island densities (~5x10@super 12@/cm@super 2@ at 2 ML) due to high defect densities on the titania surface itself. Larger islands Cu (~100 Å diameter) with uniform size distributions can be produced by deposition at room temperature followed by annealing at higher temperatures. Investigations of Ni island growth on the reconstructed titania surface are currently underway.