Microstructure and analytic equation of conical aggregate in iridium coating prepared by double glow plasma

Abstract

Dense and uniform Iridium (Ir) coating was deposited on the surface of the graphite substrate by double glow plasma. The phase identification and the morphology of the coating were examined by X-ray diffraction and scanning electron microscopy, respectively. The coating was composed of uniformly distributed regularly conical aggregates which were composed of the columnar crystals with a preferential (220) orientation. The preferential orientation was regardless of different deposition parameters and substrate properties. The analytic equation of the generatrix of the conical aggregate was determined by measuring its external dimensions. The deposition rate of the coating was up to 20 μm h⁻¹. The gap appeared within the fracture surface of the coating could result from the shadow effect of the conical aggregate. Because of the poor wetting between Ir element and C element, Ir coating grew according to the Stranski–Krastanov model.

Keywords:

• Microstructure
• Analytic equation
• Conical aggregate
• Ir coating
• Double glow plasma

This work has been supported by the National Natural Science Foundation of China (50872055/E020703).