Abstract
A heterogeneous system consisting of Pt nanoclusters on TiO 2(0 0 1)-(1×4) surface has been investigated by scanning tunneling microscopy. It has been found that Pt forms three-dimensional clusters with a narrow size distribution and that, upon annealing in vacuum, the clusters migrate to step edges via cluster diffusion mechanism mainly along the terrace atomic rows. It has also been found that the cluster size distribution and the average surface cluster density remain constant during annealing, implying that no cluster coalescence has taken place for the annealing conditions considered. A one-dimensional model has been used to study cluster diffusion on terraces and recover the diffusion coefficient from the experimental data. The model has been applied to two data sets and the results show that cluster diffusion depends on the cluster size and exhibits an Arrhenius temperature dependence, with the prefactor and activation energy depending on the cluster size. The difference between the cluster binding energy to the terrace and step edge has been found by treating the cluster system as a lattice gas on a heterogeneous surface and enforcing the principles of chemical equilibrium.
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