Growth and characterization of Rhenium Nitride coatings produced by reactive magnetron sputtering

Abstract

In this work, thin rhenium nitride (ReNx) films were deposited by reactive radio frequency (R. F.) magnetron sputtering on H13 steel and polished silicon substrates. To improve adhesion to the substrates, a Ti/TiN bilayer was deposited before the ReNx films. Substrate temperature, R.F. power, Ar and N2 gas flow, negative bias voltage, and working pressure were varied in the experiments when synthesizing the ReNx coatings. It was found that lower process pressure and nitrogen flow rate negatively affect the stabilization of coatings and lead to their delamination after they are extracted from the vacuum chamber. Meanwhile, higher nitrogen flow rate and work pressure increase the stability of the coatings by up to several days. Additionally, when the nitrogen flow rate and the negative bias voltage were increased, changes in the crystalline structure of the coatings were observed. However, when the work pressure and N2/Ar ratio were increased and the bias voltage was decreased, the stability of ReNx coatings continued even several weeks after their deposition. X-ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD) measurements validated the formation of ReN compound. The more stable deposited rhenium nitride coatings exhibited lower hardness values than the theoretical predictions for this compound, possibly due to the presence of metallic rhenium and thereby rhenium oxides, as seen in the XRD and XPS characterizations.