Tungsten oxynitride (W-O-N) thin films were deposited onto silicon (100) and quartz substrates using direct current (DC) sputtering. Composition variations in the W-O-N films were obtained by varying the nitrogen gas flow rate from 0 to 20 sccm, while keeping the total gas flow constant at 40 sccm using 20 sccm of argon with the balance comprised of oxygen. The resulting crystallinity, optical properties, and chemical composition of the DC sputtered W-O-N films were evaluated. All the W-O-N films measured were shown to be amorphous using X-ray diffraction. Spectrophotometry results indicate that the optical parameters, namely, the transmission magnitude and band gap (E-g), are highly dependent on the nitrogen content in the reactive gas mixture. Within the W-O-N system, E-g was able to be precisely tailored between 2.9 eV and 1.9 eV, corresponding to fully stoichio-metric WO3 and highly nitrided W-O-N, respectively. Rutherford backscattering spectrometry (RBS) coupled with X-ray photoelectron spectroscopy (XPS) measurements indicate that the composition of the films varies from WO3 to W-O-N composite oxynitride films. (C) 2015 Published by Elsevier B.V.