Direct observation of behaviour of Au nanoclusters on TiO2 (110) at elevated temperatures

Deposition of An on TiO2(110) at room temperature leads to nucleation of Au nanoparticles whose initial mean diameter varies between about 20 and 50 Angstrom depending on the surface coverage. The behaviour of these clusters at elevated temperatures has been studied by scanning tunnelling microscopy (STM). Annealing surfaces with submonolayer 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 Angstrom are remarkably static over a 6 h time period, but smaller clusters are observed to diffuse, mostly along the [001] 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. (C) 2001 Elsevier Science B.V. All rights reserved.