Dependence of Nitrogen/Argon Reaction Gas Amount on Structural, Mechanical and Optical Properties of Thin WN_x Films

WN_xfilms are deposited by reactive chemical vapor deposition at different amounts of nitrogen in gas mixtures. Experimental data demonstrate that nitrogen amount has a strong effect on microstructure, phase formation, texture morphology, mechanical and optical properties of the WN_x films. With increasing nitrogen a phase transition from a single WN phase with low crystallinity structure to a well-mixed crystallized hexagonal WN and face-centered-cubic W_2N phases appears. Relatively smooth morphology at lower N_2 concentration changes to a really smooth morphology and then granular with coarse surface at higher N_2 concentration. The SEM observation clearly shows a columnar structure at lower N_2 concentration and a dense nanoplates one for higher nitrogen content. The hardness of WN thin films mainly depends on the film microstructure. The absorbance peak position shifts to shorter wavelength continuously with increasing nitrogen amount and decreasing particle size.