Direct observation of behaviour of Au nanoclusters on TiO2(1 1 0) at elevated temperatures

Deposition of Au on TiO2(1 1 0) at room temperature leads to nucleation of Au nanoparticles whose initial mean diameter varies between about 20 and 50 Å depending on the surface coverage. The behaviour of these clusters at elevated temperatures has been studied by scanning tunnelling microscopy (STM). Annealing surfaces with sub-monolayer coverages of Au at 750 K leads to growth of the larger clusters, but above 873 K evaporation of gold from the surface competes with this ripening processes. At 750 K the Au coverage remains constant over many hours allowing real-time observation of the behaviour of clusters in an “STM movie”. Clusters with dimensions around 50 Å are remarkably static over a 6 h time period, but smaller clusters are observed to diffuse, mostly along the [0 0 1] direction. Events including cluster coalescence and cluster nucleation are also identified in the movie sequence. However the growth of the larger clusters at 750 K appears nonetheless to be dominated by Au atom transport across the terraces.