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

WN_x films 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_x phase with low crystallinity structure to a well-mixed crystallized hexagonal WN_x and face-centered-cubic W_2 N 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_x 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.