Thin films are generally thought of as being the product of a reaction between the surface and atoms and/or molecules in the gas phase. However, a relatively new theory, the theory of charged clusters (TCC), suggests that charged clusters nucleate in the gas phase and become the growth unit for a thin film. The aim of this study was to determine whether or not TiO2 thin film deposition by DC reactive sputtering occurs via this mechanism. TiO2 was deposited on unheated transmission electron microscopy grids to observe TiO2 clusters, as well as glass and silicon substrates to observe the resulting thin films. The results showed that TiO2 clusters were indeed produced in the chamber of a direct current reactive sputtering system. Furthermore, these clusters were observed as close as 50 mm away from the target. Clusters 3 nm and < 2 nm in diameter were found 250 mm and 50 mm away from the target, respectively. The cluster size was found to have a direct effect on the film deposited. Smaller clusters produced a facetted crystalline anatase film whereas larger clusters produced an amorphous film. (C) 2003 Elsevier B.V. All rights reserved.