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Bonding structure and morphology of chromium oxide films grown by pulsed-DC reactive magnetron sputter deposition

: Gago, R.; Vinnichenko, Mykola; Hübner, René; Redondo-Cubero, Andrés


Journal of alloys and compounds 672 (2016), pp.529-535
ISSN: 0925-8388
Journal Article
Fraunhofer IKTS ()
oxide materials; vapour deposition; atomic scale structure; NEXAFS / XANES

Chromium oxide (CrOx) thin films were grown by pulsed-DC reactive magnetron sputter deposition in an Ar/O2 discharge as a function of the O2 fraction in the gas mixture (ƒ) and for substrate temperatures, Ts, up to 450ºC. The samples were analysed by Rutherford backscattering spectrometry (RBS), spectroscopic ellipsometry (SE), atomic force microscopy (AFM), scanning (SEM) and transmission (TEM) electron microscopy, X-ray diffraction (XRD), and X-ray absorption near-edge structure (XANES). On unheated substrates, by increasing ƒ the growth rate is higher and the O/Cr ratio (x) rises from ∼2 up to ∼2.5. Inversely, by increasing Ts the atomic incorporation rate drops and x falls to ∼1.8. XRD shows that samples grown on unheated substrates are amorphous and that nanocrystalline Cr2O3 (x = 1.5) is formed by increasing Ts. In amorphous CrOx, XANES reveals the presence of multiple Cr environments that indicate the growth of mixed-valence oxides, with progressive promotion of hexavalent states with ƒ. XANES data also confirms the formation of single-phase nanocrystalline Cr2O3 at elevated Ts. These structural changes also reflect on the optical and morphological properties of the films.