Titanium dioxide thin films have been prepared by using a magnetron sputtering source placed inside a high pressure aggregation chamber. This preparation technique allows the production of fine particles from a target material through sputtering after cluster aggregation inside a high pressure (10(-1) mbar) He/Ar gas atmosphere. After that process, by channelling the clusters to a low pressure main deposition chamber, it is possible to prepare films made up by nanometric clusters. The distribution of the cluster size can be changed controlling the residence time within the aggregation zone. Films of clusters with different sizes have been deposited after varying the Ar/He atmosphere ratio and its pressure in the aggregation region. Cluster size distribution has been characterized by Atomic Force Microscopy as a function of different preparation parameters. Finally, the crystalline degree, structural phase and band-gap of the titanium oxide were obtained by means of optical spectroscopies to study the size dependence of the nanometric clusters properties. (C) 2009 Elsevier B.V. All rights reserved.