Microstructure and structure characteristics of cubic WNx compounds

Microstructure and structure of cubic WNx compounds were investigated by X-ray photoelectron spectroscopy (XPS), electron energy-loss spectroscopy (EELS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction. The samples were thin films produced by reactive dc magnetron sputtering of tungsten at various N2 partial pressures in an Ar–N2 gas mixture. The composition and structure of the films were characterized by XPS, EELS, and XRD. It was found that a two-phase structure consisting of W2N and bcc W was formed in the 0.12≤x≤0.28 range and a single-phase structure of W2N was formed at higher values of x after annealing of as-deposited samples at 600°C or above. Cross-sectional TEM studies showed that all crystalline WNx films had columnar microstructures. The average column width at stoichiometry of W2N was ∼15 nm, whereas the column grains were larger with decreasing value of x. Using the electron scattering data collected from a range of crystalline samples for calculating the pair distribution function (RDF) by Fourier transformation in real space, structural details of WN and WW bonding in W2N have been obtained.