The effect of RF power on the deposition behavior of anatase clusters

In the thin-film formation process, it is generally accepted that thin film growth occurs via a reaction between the surface and atoms and/or molecules in the gas phase. The theory of charged clusters proposes instead that a thin film is a self-assembly of charged clusters that nucleate in the gas phase. It was demonstrated that similar-sized anatase clusters have quite different deposition behaviors depending on the RF power in the reaction chamber. At 180 W a highly crystalline nanostructured film was produced. However, at 90 W, a nanopowder was deposited instead. This can be explained by the theory of charged clusters, in that the clusters become charged at higher RF power, i.e. the charging efficiency of clusters increases with increasing RF power. Lower power (90 W) did not efficiently charge the anatase clusters. Cluster charging at 180 W resulted in Coulombic repulsion, which prevented the agglomeration observed at 90 W. The self-assembly characteristics of charged clusters is highlighted by the formation of a nanostructured film.