The influence of substrate defects on the growth rate of palladium nanoparticles on a TiO2(1 1 0) surface

We investigated the growth rate of small palladium particles on TiO2(1 1 0) substrates with high and modest defect concentrations, using scanning tunnelling microscopy. The defects on the substrate surface are created as a consequence of reduction of the oxide crystal in ultra-high vacuum. The level of oxygen depletion depends on the preparation conditions, resulting in either a strongly reduced surface with a high level of oxygen depletion, or a mildly reduced surface with a modest level of oxygen depletion. After deposition of palladium at room temperature on a mildly reduced titania surface, palladium clusters predominantly cover steps. On a strongly reduced sample, clusters are smaller and distributed over the terraces. At elevated temperatures the particles grow in both cases, but the growth rate on the mildly reduced surface is higher than on the strongly reduced surface. Finally, on a mildly reduced substrate the particles are flatter than on a strongly reduced substrate.