P. Carvalho, J.M. Chappé, L. Cunha, S. Lanceros-Méndez, P. Alpuim, F. Vaz, E. Alves, C. Rousselot, J.P. Espinós, A.R. González-Elipe
Journal of Applied Physics, 103 (2008) 104907 (1-15)
This work is devoted to the investigation of decorative zirconium oxynitride,, films prepared by dc reactive magnetron sputtering, using a 17:3 nitrogen-to-oxygen-ratio gas mixture. The color of the films changed from metallic-like, very bright yellow pale, and golden yellow, for low gas mixture flows [from 0 to about (SCCM denotes cubic centimeter per minute at STP)] to red brownish for intermediate gas flows (values up to ). Associated to this color change there is a significant decrease of brightness. With further increase of the reactive gas flow, the color of the samples changed from red brownish to dark blue (samples prepared with 13 and ). The filmsdeposited with gas flows above showed only apparent colorations due to interference effects. This change in optical behavior from opaque to transparent (characteristic of a transition from metallic to insulating-type materials), promoted by the change in gas flow values, revealed that significant changes were occurring in the filmstructure and electronic properties, thus opening new potential applications for the films, beyond those of purely decorative ones. Taking this into account, the electrical behavior of the films was investigated as a function of the reactive gas flow and correlated with the observed chemical, electronic, and structural features. The variations in composition disclosed the existence of four different zones, which were correlated to different crystalline structures. For the so-called zone I, x-ray diffraction revealed the development of films with a B1 NaCl face-centered cubic zirconium nitride-type phase, with some texture changes. Increasing the reactive gas flow, the structure of the films is that of a poorly crystallized overstoichiometric nitride phase, which may be similar to that of , but with some probable oxygen inclusions within nitrogen positions. This region was characterized as zone II. Zone III was indexed as an oxynitride-type phase, similar to that of with some oxygen atoms occupying some of the nitrogen positions. Finally, occurring at the highest flow rates, zone IV was assigned to a monoclinic-type structure. The composition∕structure variations were consistent with the chemical bonding analysis carried out by x-ray photoelectron spectroscopy, which showed oxygen doping in both – and ZrN-type grown films. The electronic properties of the films exhibited significant changes from zone to zone. Resistivity measurements revealed a very wide range of values, varying from relatively highly conductive materials (for zone I) with resistivity values around few hundreds of to highly insulating films within zones III and IV, which presented resistivity values in the order of . Regarding zone II, corresponding to oxygen doped -type compounds, the observed behavior revealed resistivity values increasing steeply from about up to , indicating a systematic transition from metallic to insulating regimes.