Nanocrystalline gradient films through chemical vapor synthesis

Thick ceramic films in the systems TiO2 and Ti-O-Si consisting of nanocryst alline grains between 15 and 45 nm are prepared by a modified Chemical Vapo r Deposition (CVD) method; the Chemical Vapor Synthesis (CVS). Film formati on iri performed under helium flow in a hot wall reactor by pyrolysis of me tal-organic compounds silicon substrates. One-dimensional gradients of comp osition are achieved by adjusting precursor massflows; gradients of microst ructure are obtained by variation the reactor temperature during the proces s. The influence of process parameters; specifically temperature and precur sor flow examined. The microstructure evolves from columnar grains; Typical for CVD; To nanocrystalline grains creating an increasing porosity normal to the substrate. (C) 2001 Acta Materialia Inc. Published by Elsevier Scien ce Ltd. All rights reserved.