Grazing-incidence X-ray scattering study of the microstructure of tungsten–carbon films

The microstructure of a coating deposited onto a tungsten carbide layer by cathodic sputtering assisted by chemical vapour deposition (CVD) has been analysed by small-angle scattering of X-rays (SAXS) with a conventional laboratory set-up specially adapted for grazing incidence. Anomalous-scattering measurements have also been performed at LURE, the French synchrotron-radiation facility at Orsay with the aim of characterizing the structure of phases present in the coating. SAXS results reveal the existence of very small precipitates; the size of these precipitates determined from the use of the Guinier approximation is about 16 Å, the correlation length deduced from the position of the peak in the small-angle scattering pattern is about 36 Å. The value of the experimental integrated intensity and the variation of the observed intensities with photon energy lead to the conclusion that these nanocrystals are highly enriched in tungsten and embedded in a carbon-based matrix having a weak electronic density. Electron diffraction results support the assumption of the presence of β-WC_{1 − x}, an unstable high-temperature phase. Furthermore, the low electronic density of the matrix is in agreement with face-centred-cubic carbon recently proposed in the literature.