N.M.G. Parreira

On the Structural Evaluation of Unbiased W-O-N Sputtered Coatings

Tungsten oxynitride films (WOxNy) were deposited with a chemical composition in the range of 0 < x < 1 and 0 < y < 1. For the W-N system, the α-W, β-W, and β-W2N phases were identified according to the amount of nitrogen. In the W-O-N system the structure depended on the amount of oxygen. For an oxygen fraction, fO2 = CO/(CO+CN), smaller than 0.46 the β-W2N phase is evident, whereas above that value the structure became amorphous.

TEM Characterization of W-O-N Coatings

Recently, a new class of coatings based on oxynitrides has drawn much attention in the research field as well as in industrial applications, as shown by either the large numbers of recent publications on TM O N systems (TM—transition metal) such as Ti-O-N, Zr-O-N and Ta-O-N, or the development of Si O-N for opto-electronic devices. The properties of these coatings are related to the chemical composition and the structural arrangement. However, the knowledge about the structure of TM-O-N systems is very limited, especially how the structural arrangement of the non-metallic elements is in the lattices. To the best of our knowledge, only a few studies exist on the development of structural models for oxynitrides, based on XRD and/or XPS analysis, as e.g. Si-O-N and Ti-O-N, or on Mossbauer spectrometry for Fe-O-N. TEM was used scarcely for the characterization of TM-O-N coatings possibly due to the damage of the structure by the electron-irradiation as it is reported for Cr-O-N. This work is aimed at the crystallographic understanding of W-O-N sputtered films by using TEM and HR TEM techniques for complementing the information provided by XRD characterization.