The preferential crystallographic orientation of sputter deposited thin layers has been investigated intensively due to its technological importance. In this work, layers typically a few hundred nanometres were deposited on non-aligned polycrystalline stainless steel or glass substrates by unbalanced reactive magnetron sputtering. The influence of the reactive gas flow on the resulting preferential orientation and microstructure was investigated for thin films of yttria-stabilized zirconia (YSZ) and titanium nitride (TiN). It was observed that the preferential orientation of TiN changed from [111] to [002], while the preferential orientation of YSZ changed from [002] to a mixture of 30% [220] and 70% [111] with increasing reactive gas flow. A clear correlation between the variation in the plasma composition-which was investigated by energy-resolved mass spectroscopy-and the resulting microstructure and preferential orientation was observed. Based on this correlation, a model for the mechanism of preferential orientation is proposed. (c) 2005 Elsevier B.V. All rights reserved.